From 559b3bbfa978ce3b23dc9c52d09a0eddca52c439 Mon Sep 17 00:00:00 2001
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Date: Thu, 27 Mar 2025 10:06:10 -0400
Subject: [PATCH 1/9] locking/percpu-rwsem: add freezable alternative to
 down_read

Percpu-rwsems are used for superblock locking.  However, we know the
read percpu-rwsem we take for sb_start_write() on a frozen filesystem
needs not to inhibit system from suspending or hibernating.  That
means it needs to wait with TASK_UNINTERRUPTIBLE | TASK_FREEZABLE.

Introduce a new percpu_down_read_freezable() that allows us to control
whether TASK_FREEZABLE is added to the wait flags.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Link: https://lore.kernel.org/r/20250327140613.25178-2-James.Bottomley@HansenPartnership.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 include/linux/percpu-rwsem.h  | 20 ++++++++++++++++----
 kernel/locking/percpu-rwsem.c | 13 ++++++++-----
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index af7d75ede619..288f5235649a 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -43,9 +43,10 @@ is_static struct percpu_rw_semaphore name = {				\
 #define DEFINE_STATIC_PERCPU_RWSEM(name)	\
 	__DEFINE_PERCPU_RWSEM(name, static)
 
-extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
+extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool, bool);
 
-static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
+static inline void percpu_down_read_internal(struct percpu_rw_semaphore *sem,
+					     bool freezable)
 {
 	might_sleep();
 
@@ -63,7 +64,7 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
 	if (likely(rcu_sync_is_idle(&sem->rss)))
 		this_cpu_inc(*sem->read_count);
 	else
-		__percpu_down_read(sem, false); /* Unconditional memory barrier */
+		__percpu_down_read(sem, false, freezable); /* Unconditional memory barrier */
 	/*
 	 * The preempt_enable() prevents the compiler from
 	 * bleeding the critical section out.
@@ -71,6 +72,17 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
 	preempt_enable();
 }
 
+static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
+{
+	percpu_down_read_internal(sem, false);
+}
+
+static inline void percpu_down_read_freezable(struct percpu_rw_semaphore *sem,
+					      bool freeze)
+{
+	percpu_down_read_internal(sem, freeze);
+}
+
 static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
 {
 	bool ret = true;
@@ -82,7 +94,7 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
 	if (likely(rcu_sync_is_idle(&sem->rss)))
 		this_cpu_inc(*sem->read_count);
 	else
-		ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
+		ret = __percpu_down_read(sem, true, false); /* Unconditional memory barrier */
 	preempt_enable();
 	/*
 	 * The barrier() from preempt_enable() prevents the compiler from
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index d6964fc29f51..ef234469baac 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -138,7 +138,8 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
 	return !reader; /* wake (readers until) 1 writer */
 }
 
-static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
+static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader,
+			      bool freeze)
 {
 	DEFINE_WAIT_FUNC(wq_entry, percpu_rwsem_wake_function);
 	bool wait;
@@ -156,7 +157,8 @@ static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
 	spin_unlock_irq(&sem->waiters.lock);
 
 	while (wait) {
-		set_current_state(TASK_UNINTERRUPTIBLE);
+		set_current_state(TASK_UNINTERRUPTIBLE |
+				  (freeze ? TASK_FREEZABLE : 0));
 		if (!smp_load_acquire(&wq_entry.private))
 			break;
 		schedule();
@@ -164,7 +166,8 @@ static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
 	__set_current_state(TASK_RUNNING);
 }
 
-bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
+bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try,
+				bool freeze)
 {
 	if (__percpu_down_read_trylock(sem))
 		return true;
@@ -174,7 +177,7 @@ bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
 
 	trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_READ);
 	preempt_enable();
-	percpu_rwsem_wait(sem, /* .reader = */ true);
+	percpu_rwsem_wait(sem, /* .reader = */ true, freeze);
 	preempt_disable();
 	trace_contention_end(sem, 0);
 
@@ -237,7 +240,7 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem)
 	 */
 	if (!__percpu_down_write_trylock(sem)) {
 		trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);
-		percpu_rwsem_wait(sem, /* .reader = */ false);
+		percpu_rwsem_wait(sem, /* .reader = */ false, false);
 		contended = true;
 	}
 

From f73bae83675b860cae9f58dba233b6be92e750ca Mon Sep 17 00:00:00 2001
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Date: Thu, 27 Mar 2025 10:06:11 -0400
Subject: [PATCH 2/9] fs: allow all writers to be frozen

During freeze/thaw we need to be able to freeze all writers during
suspend/hibernate. Otherwise tasks such as systemd-journald that mmap a
file and write to it will not be frozen after we've already frozen the
filesystem.

This has some risk of not being able to freeze processes in case a
process has acquired SB_FREEZE_PAGEFAULT under mmap_sem or
SB_FREEZE_INTERNAL under some other filesytem specific lock. If the
filesystem is frozen, a task can block on the frozen filesystem with
e.g., mmap_sem held. If some other task then blocks on grabbing that
mmap_sem, hibernation ill fail because it is unable to hibernate a task
holding mmap_sem. This could be fixed by making a range of filesystem
related locks use freezable sleeping. That's impractical and not
warranted just for suspend/hibernate. Assume that this is an infrequent
problem and we've given userspace a way to skip filesystem freezing
through a sysfs file.

Link: https://lore.kernel.org/r/20250402-work-freeze-v2-2-6719a97b52ac@kernel.org
Link: https://lore.kernel.org/r/20250327140613.25178-3-James.Bottomley@HansenPartnership.com
[brauner: make all freeze levels set TASK_FREEZABLE and rewrite commit message]
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 include/linux/fs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e..35b81f497904 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1780,7 +1780,7 @@ static inline void __sb_end_write(struct super_block *sb, int level)
 
 static inline void __sb_start_write(struct super_block *sb, int level)
 {
-	percpu_down_read(sb->s_writers.rw_sem + level - 1);
+	percpu_down_read_freezable(sb->s_writers.rw_sem + level - 1, true);
 }
 
 static inline bool __sb_start_write_trylock(struct super_block *sb, int level)

From af7551cf13cf7fb1d4f939db4f1f24c00550ed57 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Sat, 29 Mar 2025 09:42:14 +0100
Subject: [PATCH 3/9] super: remove pointless s_root checks

The locking guarantees that the superblock is alive and sb->s_root is
still set. Remove the pointless check.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-1-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/super.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 97a17f9d9023..dc14f4bf73a6 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -930,8 +930,7 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 
 		locked = super_lock_shared(sb);
 		if (locked) {
-			if (sb->s_root)
-				f(sb, arg);
+			f(sb, arg);
 			super_unlock_shared(sb);
 		}
 
@@ -967,11 +966,8 @@ void iterate_supers_type(struct file_system_type *type,
 		spin_unlock(&sb_lock);
 
 		locked = super_lock_shared(sb);
-		if (locked) {
-			if (sb->s_root)
-				f(sb, arg);
-			super_unlock_shared(sb);
-		}
+		if (locked)
+			f(sb, arg);
 
 		spin_lock(&sb_lock);
 		if (p)
@@ -991,18 +987,15 @@ struct super_block *user_get_super(dev_t dev, bool excl)
 
 	spin_lock(&sb_lock);
 	list_for_each_entry(sb, &super_blocks, s_list) {
-		if (sb->s_dev ==  dev) {
+		if (sb->s_dev == dev) {
 			bool locked;
 
 			sb->s_count++;
 			spin_unlock(&sb_lock);
 			/* still alive? */
 			locked = super_lock(sb, excl);
-			if (locked) {
-				if (sb->s_root)
-					return sb;
-				super_unlock(sb, excl);
-			}
+			if (locked)
+				return sb; /* caller will drop */
 			/* nope, got unmounted */
 			spin_lock(&sb_lock);
 			__put_super(sb);

From 484caf5e117a9334a08b1d69542e1065be4b30ab Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Sat, 29 Mar 2025 09:42:15 +0100
Subject: [PATCH 4/9] super: simplify user_get_super()

Make it easier to read and remove one level of identation.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-2-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/super.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index dc14f4bf73a6..b1acfc38ba0c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -987,20 +987,21 @@ struct super_block *user_get_super(dev_t dev, bool excl)
 
 	spin_lock(&sb_lock);
 	list_for_each_entry(sb, &super_blocks, s_list) {
-		if (sb->s_dev == dev) {
-			bool locked;
+		bool locked;
 
-			sb->s_count++;
-			spin_unlock(&sb_lock);
-			/* still alive? */
-			locked = super_lock(sb, excl);
-			if (locked)
-				return sb; /* caller will drop */
-			/* nope, got unmounted */
-			spin_lock(&sb_lock);
-			__put_super(sb);
-			break;
-		}
+		if (sb->s_dev != dev)
+			continue;
+
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		locked = super_lock(sb, excl);
+		if (locked)
+			return sb;
+
+		spin_lock(&sb_lock);
+		__put_super(sb);
+		break;
 	}
 	spin_unlock(&sb_lock);
 	return NULL;

From 6920e3388ba4c66b0468d43bb7a373f5fff15d35 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Sat, 29 Mar 2025 09:42:16 +0100
Subject: [PATCH 5/9] super: skip dying superblocks early

Make all iterators uniform by performing an early check whether the
superblock is dying.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-3-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/super.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index b1acfc38ba0c..c67ea3cdda41 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -925,6 +925,9 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 	list_for_each_entry(sb, &super_blocks, s_list) {
 		bool locked;
 
+		if (super_flags(sb, SB_DYING))
+			continue;
+
 		sb->s_count++;
 		spin_unlock(&sb_lock);
 
@@ -962,6 +965,9 @@ void iterate_supers_type(struct file_system_type *type,
 	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
 		bool locked;
 
+		if (super_flags(sb, SB_DYING))
+			continue;
+
 		sb->s_count++;
 		spin_unlock(&sb_lock);
 

From 2992476528aeecbaee17ba0a6396a817481205a3 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Sat, 29 Mar 2025 09:42:17 +0100
Subject: [PATCH 6/9] super: use a common iterator (Part 1)

Use a common iterator for all callbacks.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-4-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/super.c         | 67 +++++++++-------------------------------------
 include/linux/fs.h |  6 ++++-
 2 files changed, 18 insertions(+), 55 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index c67ea3cdda41..0dd208804a74 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -887,37 +887,7 @@ void drop_super_exclusive(struct super_block *sb)
 }
 EXPORT_SYMBOL(drop_super_exclusive);
 
-static void __iterate_supers(void (*f)(struct super_block *))
-{
-	struct super_block *sb, *p = NULL;
-
-	spin_lock(&sb_lock);
-	list_for_each_entry(sb, &super_blocks, s_list) {
-		if (super_flags(sb, SB_DYING))
-			continue;
-		sb->s_count++;
-		spin_unlock(&sb_lock);
-
-		f(sb);
-
-		spin_lock(&sb_lock);
-		if (p)
-			__put_super(p);
-		p = sb;
-	}
-	if (p)
-		__put_super(p);
-	spin_unlock(&sb_lock);
-}
-/**
- *	iterate_supers - call function for all active superblocks
- *	@f: function to call
- *	@arg: argument to pass to it
- *
- *	Scans the superblock list and calls given function, passing it
- *	locked superblock and given argument.
- */
-void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl)
 {
 	struct super_block *sb, *p = NULL;
 
@@ -927,14 +897,13 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 
 		if (super_flags(sb, SB_DYING))
 			continue;
-
 		sb->s_count++;
 		spin_unlock(&sb_lock);
 
-		locked = super_lock_shared(sb);
+		locked = super_lock(sb, excl);
 		if (locked) {
 			f(sb, arg);
-			super_unlock_shared(sb);
+			super_unlock(sb, excl);
 		}
 
 		spin_lock(&sb_lock);
@@ -1111,11 +1080,9 @@ int reconfigure_super(struct fs_context *fc)
 	return retval;
 }
 
-static void do_emergency_remount_callback(struct super_block *sb)
+static void do_emergency_remount_callback(struct super_block *sb, void *unused)
 {
-	bool locked = super_lock_excl(sb);
-
-	if (locked && sb->s_root && sb->s_bdev && !sb_rdonly(sb)) {
+	if (sb->s_bdev && !sb_rdonly(sb)) {
 		struct fs_context *fc;
 
 		fc = fs_context_for_reconfigure(sb->s_root,
@@ -1126,13 +1093,11 @@ static void do_emergency_remount_callback(struct super_block *sb)
 			put_fs_context(fc);
 		}
 	}
-	if (locked)
-		super_unlock_excl(sb);
 }
 
 static void do_emergency_remount(struct work_struct *work)
 {
-	__iterate_supers(do_emergency_remount_callback);
+	__iterate_supers(do_emergency_remount_callback, NULL, true);
 	kfree(work);
 	printk("Emergency Remount complete\n");
 }
@@ -1148,24 +1113,18 @@ void emergency_remount(void)
 	}
 }
 
-static void do_thaw_all_callback(struct super_block *sb)
+static void do_thaw_all_callback(struct super_block *sb, void *unused)
 {
-	bool locked = super_lock_excl(sb);
-
-	if (locked && sb->s_root) {
-		if (IS_ENABLED(CONFIG_BLOCK))
-			while (sb->s_bdev && !bdev_thaw(sb->s_bdev))
-				pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
-		thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
-		return;
-	}
-	if (locked)
-		super_unlock_excl(sb);
+	if (IS_ENABLED(CONFIG_BLOCK))
+		while (sb->s_bdev && !bdev_thaw(sb->s_bdev))
+			pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
+	thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
+	return;
 }
 
 static void do_thaw_all(struct work_struct *work)
 {
-	__iterate_supers(do_thaw_all_callback);
+	__iterate_supers(do_thaw_all_callback, NULL, true);
 	kfree(work);
 	printk(KERN_WARNING "Emergency Thaw complete\n");
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 35b81f497904..5e007bffd00e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3515,7 +3515,11 @@ extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern void drop_super(struct super_block *sb);
 extern void drop_super_exclusive(struct super_block *sb);
-extern void iterate_supers(void (*)(struct super_block *, void *), void *);
+void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl);
+static inline void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+{
+	__iterate_supers(f, arg, false);
+}
 extern void iterate_supers_type(struct file_system_type *,
 			        void (*)(struct super_block *, void *), void *);
 

From b47e42d10e8c20525febccbd6e0dc8528861aea4 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Sat, 29 Mar 2025 09:42:18 +0100
Subject: [PATCH 7/9] super: use common iterator (Part 2)

Use a common iterator for all callbacks. We could go for something even
more elaborate (advance step-by-step similar to iov_iter) but I really
don't think this is warranted.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-5-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/super.c         | 48 +++++++++++++++++++++++++++++++++++++---------
 include/linux/fs.h |  6 +-----
 2 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 0dd208804a74..796e7f402a41 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -887,21 +887,46 @@ void drop_super_exclusive(struct super_block *sb)
 }
 EXPORT_SYMBOL(drop_super_exclusive);
 
-void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl)
+enum super_iter_flags_t {
+	SUPER_ITER_EXCL		= (1U << 0),
+	SUPER_ITER_UNLOCKED	= (1U << 1),
+	SUPER_ITER_REVERSE	= (1U << 2),
+};
+
+static inline struct super_block *first_super(enum super_iter_flags_t flags)
+{
+	if (flags & SUPER_ITER_REVERSE)
+		return list_last_entry(&super_blocks, struct super_block, s_list);
+	return list_first_entry(&super_blocks, struct super_block, s_list);
+}
+
+static inline struct super_block *next_super(struct super_block *sb,
+					     enum super_iter_flags_t flags)
+{
+	if (flags & SUPER_ITER_REVERSE)
+		return list_prev_entry(sb, s_list);
+	return list_next_entry(sb, s_list);
+}
+
+static void __iterate_supers(void (*f)(struct super_block *, void *), void *arg,
+			     enum super_iter_flags_t flags)
 {
 	struct super_block *sb, *p = NULL;
+	bool excl = flags & SUPER_ITER_EXCL;
 
-	spin_lock(&sb_lock);
-	list_for_each_entry(sb, &super_blocks, s_list) {
-		bool locked;
+	guard(spinlock)(&sb_lock);
 
+	for (sb = first_super(flags);
+	     !list_entry_is_head(sb, &super_blocks, s_list);
+	     sb = next_super(sb, flags)) {
 		if (super_flags(sb, SB_DYING))
 			continue;
 		sb->s_count++;
 		spin_unlock(&sb_lock);
 
-		locked = super_lock(sb, excl);
-		if (locked) {
+		if (flags & SUPER_ITER_UNLOCKED) {
+			f(sb, arg);
+		} else if (super_lock(sb, excl)) {
 			f(sb, arg);
 			super_unlock(sb, excl);
 		}
@@ -913,7 +938,11 @@ void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool e
 	}
 	if (p)
 		__put_super(p);
-	spin_unlock(&sb_lock);
+}
+
+void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+{
+	__iterate_supers(f, arg, 0);
 }
 
 /**
@@ -1097,7 +1126,8 @@ static void do_emergency_remount_callback(struct super_block *sb, void *unused)
 
 static void do_emergency_remount(struct work_struct *work)
 {
-	__iterate_supers(do_emergency_remount_callback, NULL, true);
+	__iterate_supers(do_emergency_remount_callback, NULL,
+			 SUPER_ITER_EXCL | SUPER_ITER_REVERSE);
 	kfree(work);
 	printk("Emergency Remount complete\n");
 }
@@ -1124,7 +1154,7 @@ static void do_thaw_all_callback(struct super_block *sb, void *unused)
 
 static void do_thaw_all(struct work_struct *work)
 {
-	__iterate_supers(do_thaw_all_callback, NULL, true);
+	__iterate_supers(do_thaw_all_callback, NULL, SUPER_ITER_EXCL);
 	kfree(work);
 	printk(KERN_WARNING "Emergency Thaw complete\n");
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5e007bffd00e..96f8c8a794ea 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3515,11 +3515,7 @@ extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern void drop_super(struct super_block *sb);
 extern void drop_super_exclusive(struct super_block *sb);
-void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl);
-static inline void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
-{
-	__iterate_supers(f, arg, false);
-}
+extern void iterate_supers(void (*f)(struct super_block *, void *), void *arg);
 extern void iterate_supers_type(struct file_system_type *,
 			        void (*)(struct super_block *, void *), void *);
 

From 62a2175ddf7e72941868f164b7c1f92e00f213bd Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Fri, 4 Apr 2025 21:02:28 +0200
Subject: [PATCH 8/9] gfs2: pass through holder from the VFS for freeze/thaw

The filesystem's freeze/thaw functions can be called from contexts where
the holder isn't userspace but the kernel, e.g., during systemd
suspend/hibernate. So pass through the freeze/thaw flags from the VFS
instead of hard-coding them.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/gfs2/super.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 44e5658b896c..a3fe95e519cb 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -674,7 +674,7 @@ static int gfs2_sync_fs(struct super_block *sb, int wait)
 	return sdp->sd_log_error;
 }
 
-static int gfs2_do_thaw(struct gfs2_sbd *sdp)
+static int gfs2_do_thaw(struct gfs2_sbd *sdp, enum freeze_holder who)
 {
 	struct super_block *sb = sdp->sd_vfs;
 	int error;
@@ -682,7 +682,7 @@ static int gfs2_do_thaw(struct gfs2_sbd *sdp)
 	error = gfs2_freeze_lock_shared(sdp);
 	if (error)
 		goto fail;
-	error = thaw_super(sb, FREEZE_HOLDER_USERSPACE);
+	error = thaw_super(sb, who);
 	if (!error)
 		return 0;
 
@@ -710,7 +710,7 @@ void gfs2_freeze_func(struct work_struct *work)
 	gfs2_freeze_unlock(sdp);
 	set_bit(SDF_FROZEN, &sdp->sd_flags);
 
-	error = gfs2_do_thaw(sdp);
+	error = gfs2_do_thaw(sdp, FREEZE_HOLDER_USERSPACE);
 	if (error)
 		goto out;
 
@@ -728,6 +728,7 @@ void gfs2_freeze_func(struct work_struct *work)
 /**
  * gfs2_freeze_super - prevent further writes to the filesystem
  * @sb: the VFS structure for the filesystem
+ * @who: freeze flags
  *
  */
 
@@ -744,7 +745,7 @@ static int gfs2_freeze_super(struct super_block *sb, enum freeze_holder who)
 	}
 
 	for (;;) {
-		error = freeze_super(sb, FREEZE_HOLDER_USERSPACE);
+		error = freeze_super(sb, who);
 		if (error) {
 			fs_info(sdp, "GFS2: couldn't freeze filesystem: %d\n",
 				error);
@@ -758,7 +759,7 @@ static int gfs2_freeze_super(struct super_block *sb, enum freeze_holder who)
 			break;
 		}
 
-		error = gfs2_do_thaw(sdp);
+		error = gfs2_do_thaw(sdp, who);
 		if (error)
 			goto out;
 
@@ -796,6 +797,7 @@ static int gfs2_freeze_fs(struct super_block *sb)
 /**
  * gfs2_thaw_super - reallow writes to the filesystem
  * @sb: the VFS structure for the filesystem
+ * @who: freeze flags
  *
  */
 
@@ -814,7 +816,7 @@ static int gfs2_thaw_super(struct super_block *sb, enum freeze_holder who)
 	atomic_inc(&sb->s_active);
 	gfs2_freeze_unlock(sdp);
 
-	error = gfs2_do_thaw(sdp);
+	error = gfs2_do_thaw(sdp, who);
 
 	if (!error) {
 		clear_bit(SDF_FREEZE_INITIATOR, &sdp->sd_flags);

From 1af3331764b9356fadc4652af77bbbc97f3d7f78 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Sat, 29 Mar 2025 09:42:19 +0100
Subject: [PATCH 9/9] super: add filesystem freezing helpers for suspend and
 hibernate

Allow the power subsystem to support filesystem freeze for
suspend and hibernate.

For some kernel subsystems it is paramount that they are guaranteed that
they are the owner of the freeze to avoid any risk of deadlocks. This is
the case for the power subsystem. Enable it to recognize whether it did
actually freeze the filesystem.

If userspace has 10 filesystems and suspend/hibernate manges to freeze 5
and then fails on the 6th for whatever odd reason (current or future)
then power needs to undo the freeze of the first 5 filesystems. It can't
just walk the list again because while it's unlikely that a new
filesystem got added in the meantime it still cannot tell which
filesystems the power subsystem actually managed to get a freeze
reference count on that needs to be dropped during thaw.

There's various ways out of this ugliness. For example, record the
filesystems the power subsystem managed to freeze on a temporary list in
the callbacks and then walk that list backwards during thaw to undo the
freezing or make sure that the power subsystem just actually exclusively
freezes things it can freeze and marking such filesystems as being owned
by power for the duration of the suspend or resume cycle. I opted for
the latter as that seemed the clean thing to do even if it means more
code changes.

If hibernation races with filesystem freezing (e.g. DM reconfiguration),
then hibernation need not freeze a filesystem because it's already
frozen but userspace may thaw the filesystem before hibernation actually
happens.

If the race happens the other way around, DM reconfiguration may
unexpectedly fail with EBUSY.

So allow FREEZE_EXCL to nest with other holders. An exclusive freezer
cannot be undone by any of the other concurrent freezers.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-6-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/f2fs/gc.c                |   6 +-
 fs/gfs2/super.c             |  22 +++--
 fs/gfs2/sys.c               |   4 +-
 fs/ioctl.c                  |   8 +-
 fs/super.c                  | 171 +++++++++++++++++++++++++++++++++---
 fs/xfs/scrub/fscounters.c   |   4 +-
 fs/xfs/xfs_notify_failure.c |   6 +-
 include/linux/fs.h          |  15 +++-
 8 files changed, 196 insertions(+), 40 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 2b8f9239bede..3e8af62c9e15 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -2271,12 +2271,12 @@ int f2fs_resize_fs(struct file *filp, __u64 block_count)
 	if (err)
 		return err;
 
-	err = freeze_super(sbi->sb, FREEZE_HOLDER_USERSPACE);
+	err = freeze_super(sbi->sb, FREEZE_HOLDER_USERSPACE, NULL);
 	if (err)
 		return err;
 
 	if (f2fs_readonly(sbi->sb)) {
-		err = thaw_super(sbi->sb, FREEZE_HOLDER_USERSPACE);
+		err = thaw_super(sbi->sb, FREEZE_HOLDER_USERSPACE, NULL);
 		if (err)
 			return err;
 		return -EROFS;
@@ -2333,6 +2333,6 @@ int f2fs_resize_fs(struct file *filp, __u64 block_count)
 out_err:
 	f2fs_up_write(&sbi->cp_global_sem);
 	f2fs_up_write(&sbi->gc_lock);
-	thaw_super(sbi->sb, FREEZE_HOLDER_USERSPACE);
+	thaw_super(sbi->sb, FREEZE_HOLDER_USERSPACE, NULL);
 	return err;
 }
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index a3fe95e519cb..436cf168a9f5 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -674,7 +674,7 @@ static int gfs2_sync_fs(struct super_block *sb, int wait)
 	return sdp->sd_log_error;
 }
 
-static int gfs2_do_thaw(struct gfs2_sbd *sdp, enum freeze_holder who)
+static int gfs2_do_thaw(struct gfs2_sbd *sdp, enum freeze_holder who, const void *freeze_owner)
 {
 	struct super_block *sb = sdp->sd_vfs;
 	int error;
@@ -682,7 +682,7 @@ static int gfs2_do_thaw(struct gfs2_sbd *sdp, enum freeze_holder who)
 	error = gfs2_freeze_lock_shared(sdp);
 	if (error)
 		goto fail;
-	error = thaw_super(sb, who);
+	error = thaw_super(sb, who, freeze_owner);
 	if (!error)
 		return 0;
 
@@ -703,14 +703,14 @@ void gfs2_freeze_func(struct work_struct *work)
 	if (test_bit(SDF_FROZEN, &sdp->sd_flags))
 		goto freeze_failed;
 
-	error = freeze_super(sb, FREEZE_HOLDER_USERSPACE);
+	error = freeze_super(sb, FREEZE_HOLDER_USERSPACE, NULL);
 	if (error)
 		goto freeze_failed;
 
 	gfs2_freeze_unlock(sdp);
 	set_bit(SDF_FROZEN, &sdp->sd_flags);
 
-	error = gfs2_do_thaw(sdp, FREEZE_HOLDER_USERSPACE);
+	error = gfs2_do_thaw(sdp, FREEZE_HOLDER_USERSPACE, NULL);
 	if (error)
 		goto out;
 
@@ -729,10 +729,12 @@ void gfs2_freeze_func(struct work_struct *work)
  * gfs2_freeze_super - prevent further writes to the filesystem
  * @sb: the VFS structure for the filesystem
  * @who: freeze flags
+ * @freeze_owner: owner of the freeze
  *
  */
 
-static int gfs2_freeze_super(struct super_block *sb, enum freeze_holder who)
+static int gfs2_freeze_super(struct super_block *sb, enum freeze_holder who,
+			     const void *freeze_owner)
 {
 	struct gfs2_sbd *sdp = sb->s_fs_info;
 	int error;
@@ -745,7 +747,7 @@ static int gfs2_freeze_super(struct super_block *sb, enum freeze_holder who)
 	}
 
 	for (;;) {
-		error = freeze_super(sb, who);
+		error = freeze_super(sb, who, freeze_owner);
 		if (error) {
 			fs_info(sdp, "GFS2: couldn't freeze filesystem: %d\n",
 				error);
@@ -759,7 +761,7 @@ static int gfs2_freeze_super(struct super_block *sb, enum freeze_holder who)
 			break;
 		}
 
-		error = gfs2_do_thaw(sdp, who);
+		error = gfs2_do_thaw(sdp, who, freeze_owner);
 		if (error)
 			goto out;
 
@@ -798,10 +800,12 @@ static int gfs2_freeze_fs(struct super_block *sb)
  * gfs2_thaw_super - reallow writes to the filesystem
  * @sb: the VFS structure for the filesystem
  * @who: freeze flags
+ * @freeze_owner: owner of the freeze
  *
  */
 
-static int gfs2_thaw_super(struct super_block *sb, enum freeze_holder who)
+static int gfs2_thaw_super(struct super_block *sb, enum freeze_holder who,
+			   const void *freeze_owner)
 {
 	struct gfs2_sbd *sdp = sb->s_fs_info;
 	int error;
@@ -816,7 +820,7 @@ static int gfs2_thaw_super(struct super_block *sb, enum freeze_holder who)
 	atomic_inc(&sb->s_active);
 	gfs2_freeze_unlock(sdp);
 
-	error = gfs2_do_thaw(sdp, who);
+	error = gfs2_do_thaw(sdp, who, freeze_owner);
 
 	if (!error) {
 		clear_bit(SDF_FREEZE_INITIATOR, &sdp->sd_flags);
diff --git a/fs/gfs2/sys.c b/fs/gfs2/sys.c
index ecc699f8d9fc..748125653d6c 100644
--- a/fs/gfs2/sys.c
+++ b/fs/gfs2/sys.c
@@ -174,10 +174,10 @@ static ssize_t freeze_store(struct gfs2_sbd *sdp, const char *buf, size_t len)
 
 	switch (n) {
 	case 0:
-		error = thaw_super(sdp->sd_vfs, FREEZE_HOLDER_USERSPACE);
+		error = thaw_super(sdp->sd_vfs, FREEZE_HOLDER_USERSPACE, NULL);
 		break;
 	case 1:
-		error = freeze_super(sdp->sd_vfs, FREEZE_HOLDER_USERSPACE);
+		error = freeze_super(sdp->sd_vfs, FREEZE_HOLDER_USERSPACE, NULL);
 		break;
 	default:
 		return -EINVAL;
diff --git a/fs/ioctl.c b/fs/ioctl.c
index c91fd2b46a77..bedc83fc2f20 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -396,8 +396,8 @@ static int ioctl_fsfreeze(struct file *filp)
 
 	/* Freeze */
 	if (sb->s_op->freeze_super)
-		return sb->s_op->freeze_super(sb, FREEZE_HOLDER_USERSPACE);
-	return freeze_super(sb, FREEZE_HOLDER_USERSPACE);
+		return sb->s_op->freeze_super(sb, FREEZE_HOLDER_USERSPACE, NULL);
+	return freeze_super(sb, FREEZE_HOLDER_USERSPACE, NULL);
 }
 
 static int ioctl_fsthaw(struct file *filp)
@@ -409,8 +409,8 @@ static int ioctl_fsthaw(struct file *filp)
 
 	/* Thaw */
 	if (sb->s_op->thaw_super)
-		return sb->s_op->thaw_super(sb, FREEZE_HOLDER_USERSPACE);
-	return thaw_super(sb, FREEZE_HOLDER_USERSPACE);
+		return sb->s_op->thaw_super(sb, FREEZE_HOLDER_USERSPACE, NULL);
+	return thaw_super(sb, FREEZE_HOLDER_USERSPACE, NULL);
 }
 
 static int ioctl_file_dedupe_range(struct file *file,
diff --git a/fs/super.c b/fs/super.c
index 796e7f402a41..281790625b18 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -39,7 +39,8 @@
 #include <uapi/linux/mount.h>
 #include "internal.h"
 
-static int thaw_super_locked(struct super_block *sb, enum freeze_holder who);
+static int thaw_super_locked(struct super_block *sb, enum freeze_holder who,
+			     const void *freeze_owner);
 
 static LIST_HEAD(super_blocks);
 static DEFINE_SPINLOCK(sb_lock);
@@ -1148,7 +1149,7 @@ static void do_thaw_all_callback(struct super_block *sb, void *unused)
 	if (IS_ENABLED(CONFIG_BLOCK))
 		while (sb->s_bdev && !bdev_thaw(sb->s_bdev))
 			pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
-	thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
+	thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE, NULL);
 	return;
 }
 
@@ -1175,6 +1176,66 @@ void emergency_thaw_all(void)
 	}
 }
 
+static inline bool get_active_super(struct super_block *sb)
+{
+	bool active = false;
+
+	if (super_lock_excl(sb)) {
+		active = atomic_inc_not_zero(&sb->s_active);
+		super_unlock_excl(sb);
+	}
+	return active;
+}
+
+static const char *filesystems_freeze_ptr = "filesystems_freeze";
+
+static void filesystems_freeze_callback(struct super_block *sb, void *unused)
+{
+	if (!sb->s_op->freeze_fs && !sb->s_op->freeze_super)
+		return;
+
+	if (!get_active_super(sb))
+		return;
+
+	if (sb->s_op->freeze_super)
+		sb->s_op->freeze_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL,
+				       filesystems_freeze_ptr);
+	else
+		freeze_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL,
+			     filesystems_freeze_ptr);
+
+	deactivate_super(sb);
+}
+
+void filesystems_freeze(void)
+{
+	__iterate_supers(filesystems_freeze_callback, NULL,
+			 SUPER_ITER_UNLOCKED | SUPER_ITER_REVERSE);
+}
+
+static void filesystems_thaw_callback(struct super_block *sb, void *unused)
+{
+	if (!sb->s_op->freeze_fs && !sb->s_op->freeze_super)
+		return;
+
+	if (!get_active_super(sb))
+		return;
+
+	if (sb->s_op->thaw_super)
+		sb->s_op->thaw_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL,
+				     filesystems_freeze_ptr);
+	else
+		thaw_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL,
+			   filesystems_freeze_ptr);
+
+	deactivate_super(sb);
+}
+
+void filesystems_thaw(void)
+{
+	__iterate_supers(filesystems_thaw_callback, NULL, SUPER_ITER_UNLOCKED);
+}
+
 static DEFINE_IDA(unnamed_dev_ida);
 
 /**
@@ -1468,10 +1529,10 @@ static int fs_bdev_freeze(struct block_device *bdev)
 
 	if (sb->s_op->freeze_super)
 		error = sb->s_op->freeze_super(sb,
-				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
+				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL);
 	else
 		error = freeze_super(sb,
-				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
+				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL);
 	if (!error)
 		error = sync_blockdev(bdev);
 	deactivate_super(sb);
@@ -1517,10 +1578,10 @@ static int fs_bdev_thaw(struct block_device *bdev)
 
 	if (sb->s_op->thaw_super)
 		error = sb->s_op->thaw_super(sb,
-				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
+				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL);
 	else
 		error = thaw_super(sb,
-				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE);
+				FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL);
 	deactivate_super(sb);
 	return error;
 }
@@ -1892,7 +1953,7 @@ static int wait_for_partially_frozen(struct super_block *sb)
 }
 
 #define FREEZE_HOLDERS (FREEZE_HOLDER_KERNEL | FREEZE_HOLDER_USERSPACE)
-#define FREEZE_FLAGS (FREEZE_HOLDERS | FREEZE_MAY_NEST)
+#define FREEZE_FLAGS (FREEZE_HOLDERS | FREEZE_MAY_NEST | FREEZE_EXCL)
 
 static inline int freeze_inc(struct super_block *sb, enum freeze_holder who)
 {
@@ -1918,11 +1979,34 @@ static inline int freeze_dec(struct super_block *sb, enum freeze_holder who)
 	return sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount;
 }
 
-static inline bool may_freeze(struct super_block *sb, enum freeze_holder who)
+static inline bool may_freeze(struct super_block *sb, enum freeze_holder who,
+			      const void *freeze_owner)
 {
+	lockdep_assert_held(&sb->s_umount);
+
 	WARN_ON_ONCE((who & ~FREEZE_FLAGS));
 	WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
 
+	if (who & FREEZE_EXCL) {
+		if (WARN_ON_ONCE(!(who & FREEZE_HOLDER_KERNEL)))
+			return false;
+		if (WARN_ON_ONCE(who & ~(FREEZE_EXCL | FREEZE_HOLDER_KERNEL)))
+			return false;
+		if (WARN_ON_ONCE(!freeze_owner))
+			return false;
+		/* This freeze already has a specific owner. */
+		if (sb->s_writers.freeze_owner)
+			return false;
+		/*
+		 * This is already frozen multiple times so we're just
+		 * going to take a reference count and mark the freeze as
+		 * being owned by the caller.
+		 */
+		if (sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount)
+			sb->s_writers.freeze_owner = freeze_owner;
+		return true;
+	}
+
 	if (who & FREEZE_HOLDER_KERNEL)
 		return (who & FREEZE_MAY_NEST) ||
 		       sb->s_writers.freeze_kcount == 0;
@@ -1932,10 +2016,61 @@ static inline bool may_freeze(struct super_block *sb, enum freeze_holder who)
 	return false;
 }
 
+static inline bool may_unfreeze(struct super_block *sb, enum freeze_holder who,
+				const void *freeze_owner)
+{
+	lockdep_assert_held(&sb->s_umount);
+
+	WARN_ON_ONCE((who & ~FREEZE_FLAGS));
+	WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
+
+	if (who & FREEZE_EXCL) {
+		if (WARN_ON_ONCE(!(who & FREEZE_HOLDER_KERNEL)))
+			return false;
+		if (WARN_ON_ONCE(who & ~(FREEZE_EXCL | FREEZE_HOLDER_KERNEL)))
+			return false;
+		if (WARN_ON_ONCE(!freeze_owner))
+			return false;
+		if (WARN_ON_ONCE(sb->s_writers.freeze_kcount == 0))
+			return false;
+		/* This isn't exclusively frozen. */
+		if (!sb->s_writers.freeze_owner)
+			return false;
+		/* This isn't exclusively frozen by us. */
+		if (sb->s_writers.freeze_owner != freeze_owner)
+			return false;
+		/*
+		 * This is still frozen multiple times so we're just
+		 * going to drop our reference count and undo our
+		 * exclusive freeze.
+		 */
+		if ((sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount) > 1)
+			sb->s_writers.freeze_owner = NULL;
+		return true;
+	}
+
+	if (who & FREEZE_HOLDER_KERNEL) {
+		/*
+		 * Someone's trying to steal the reference belonging to
+		 * @sb->s_writers.freeze_owner.
+		 */
+		if (sb->s_writers.freeze_kcount == 1 &&
+		    sb->s_writers.freeze_owner)
+			return false;
+		return sb->s_writers.freeze_kcount > 0;
+	}
+
+	if (who & FREEZE_HOLDER_USERSPACE)
+		return sb->s_writers.freeze_ucount > 0;
+
+	return false;
+}
+
 /**
  * freeze_super - lock the filesystem and force it into a consistent state
  * @sb: the super to lock
  * @who: context that wants to freeze
+ * @freeze_owner: owner of the freeze
  *
  * Syncs the super to make sure the filesystem is consistent and calls the fs's
  * freeze_fs.  Subsequent calls to this without first thawing the fs may return
@@ -1987,7 +2122,7 @@ static inline bool may_freeze(struct super_block *sb, enum freeze_holder who)
  * Return: If the freeze was successful zero is returned. If the freeze
  *         failed a negative error code is returned.
  */
-int freeze_super(struct super_block *sb, enum freeze_holder who)
+int freeze_super(struct super_block *sb, enum freeze_holder who, const void *freeze_owner)
 {
 	int ret;
 
@@ -1999,7 +2134,7 @@ int freeze_super(struct super_block *sb, enum freeze_holder who)
 
 retry:
 	if (sb->s_writers.frozen == SB_FREEZE_COMPLETE) {
-		if (may_freeze(sb, who))
+		if (may_freeze(sb, who, freeze_owner))
 			ret = !!WARN_ON_ONCE(freeze_inc(sb, who) == 1);
 		else
 			ret = -EBUSY;
@@ -2021,6 +2156,7 @@ int freeze_super(struct super_block *sb, enum freeze_holder who)
 	if (sb_rdonly(sb)) {
 		/* Nothing to do really... */
 		WARN_ON_ONCE(freeze_inc(sb, who) > 1);
+		sb->s_writers.freeze_owner = freeze_owner;
 		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
 		wake_up_var(&sb->s_writers.frozen);
 		super_unlock_excl(sb);
@@ -2068,6 +2204,7 @@ int freeze_super(struct super_block *sb, enum freeze_holder who)
 	 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
 	 */
 	WARN_ON_ONCE(freeze_inc(sb, who) > 1);
+	sb->s_writers.freeze_owner = freeze_owner;
 	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
 	wake_up_var(&sb->s_writers.frozen);
 	lockdep_sb_freeze_release(sb);
@@ -2082,13 +2219,17 @@ EXPORT_SYMBOL(freeze_super);
  * removes that state without releasing the other state or unlocking the
  * filesystem.
  */
-static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
+static int thaw_super_locked(struct super_block *sb, enum freeze_holder who,
+			     const void *freeze_owner)
 {
 	int error = -EINVAL;
 
 	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE)
 		goto out_unlock;
 
+	if (!may_unfreeze(sb, who, freeze_owner))
+		goto out_unlock;
+
 	/*
 	 * All freezers share a single active reference.
 	 * So just unlock in case there are any left.
@@ -2098,6 +2239,7 @@ static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
 
 	if (sb_rdonly(sb)) {
 		sb->s_writers.frozen = SB_UNFROZEN;
+		sb->s_writers.freeze_owner = NULL;
 		wake_up_var(&sb->s_writers.frozen);
 		goto out_deactivate;
 	}
@@ -2115,6 +2257,7 @@ static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
 	}
 
 	sb->s_writers.frozen = SB_UNFROZEN;
+	sb->s_writers.freeze_owner = NULL;
 	wake_up_var(&sb->s_writers.frozen);
 	sb_freeze_unlock(sb, SB_FREEZE_FS);
 out_deactivate:
@@ -2130,6 +2273,7 @@ static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
  * thaw_super -- unlock filesystem
  * @sb: the super to thaw
  * @who: context that wants to freeze
+ * @freeze_owner: owner of the freeze
  *
  * Unlocks the filesystem and marks it writeable again after freeze_super()
  * if there are no remaining freezes on the filesystem.
@@ -2143,13 +2287,14 @@ static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
  * have been frozen through the block layer via multiple block devices.
  * The filesystem remains frozen until all block devices are unfrozen.
  */
-int thaw_super(struct super_block *sb, enum freeze_holder who)
+int thaw_super(struct super_block *sb, enum freeze_holder who,
+	       const void *freeze_owner)
 {
 	if (!super_lock_excl(sb)) {
 		WARN_ON_ONCE("Dying superblock while thawing!");
 		return -EINVAL;
 	}
-	return thaw_super_locked(sb, who);
+	return thaw_super_locked(sb, who, freeze_owner);
 }
 EXPORT_SYMBOL(thaw_super);
 
diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c
index e629663e460a..9b598c5790ad 100644
--- a/fs/xfs/scrub/fscounters.c
+++ b/fs/xfs/scrub/fscounters.c
@@ -123,7 +123,7 @@ xchk_fsfreeze(
 {
 	int			error;
 
-	error = freeze_super(sc->mp->m_super, FREEZE_HOLDER_KERNEL);
+	error = freeze_super(sc->mp->m_super, FREEZE_HOLDER_KERNEL, NULL);
 	trace_xchk_fsfreeze(sc, error);
 	return error;
 }
@@ -135,7 +135,7 @@ xchk_fsthaw(
 	int			error;
 
 	/* This should always succeed, we have a kernel freeze */
-	error = thaw_super(sc->mp->m_super, FREEZE_HOLDER_KERNEL);
+	error = thaw_super(sc->mp->m_super, FREEZE_HOLDER_KERNEL, NULL);
 	trace_xchk_fsthaw(sc, error);
 	return error;
 }
diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
index ed8d8ed42f0a..3545dc1d953c 100644
--- a/fs/xfs/xfs_notify_failure.c
+++ b/fs/xfs/xfs_notify_failure.c
@@ -127,7 +127,7 @@ xfs_dax_notify_failure_freeze(
 	struct super_block	*sb = mp->m_super;
 	int			error;
 
-	error = freeze_super(sb, FREEZE_HOLDER_KERNEL);
+	error = freeze_super(sb, FREEZE_HOLDER_KERNEL, NULL);
 	if (error)
 		xfs_emerg(mp, "already frozen by kernel, err=%d", error);
 
@@ -143,7 +143,7 @@ xfs_dax_notify_failure_thaw(
 	int			error;
 
 	if (kernel_frozen) {
-		error = thaw_super(sb, FREEZE_HOLDER_KERNEL);
+		error = thaw_super(sb, FREEZE_HOLDER_KERNEL, NULL);
 		if (error)
 			xfs_emerg(mp, "still frozen after notify failure, err=%d",
 				error);
@@ -153,7 +153,7 @@ xfs_dax_notify_failure_thaw(
 	 * Also thaw userspace call anyway because the device is about to be
 	 * removed immediately.
 	 */
-	thaw_super(sb, FREEZE_HOLDER_USERSPACE);
+	thaw_super(sb, FREEZE_HOLDER_USERSPACE, NULL);
 }
 
 static int
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 96f8c8a794ea..7a3f821d2723 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1307,6 +1307,7 @@ struct sb_writers {
 	unsigned short			frozen;		/* Is sb frozen? */
 	int				freeze_kcount;	/* How many kernel freeze requests? */
 	int				freeze_ucount;	/* How many userspace freeze requests? */
+	const void			*freeze_owner;	/* Owner of the freeze */
 	struct percpu_rw_semaphore	rw_sem[SB_FREEZE_LEVELS];
 };
 
@@ -2269,6 +2270,7 @@ extern loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
  * @FREEZE_HOLDER_KERNEL: kernel wants to freeze or thaw filesystem
  * @FREEZE_HOLDER_USERSPACE: userspace wants to freeze or thaw filesystem
  * @FREEZE_MAY_NEST: whether nesting freeze and thaw requests is allowed
+ * @FREEZE_EXCL: a freeze that can only be undone by the owner
  *
  * Indicate who the owner of the freeze or thaw request is and whether
  * the freeze needs to be exclusive or can nest.
@@ -2282,6 +2284,7 @@ enum freeze_holder {
 	FREEZE_HOLDER_KERNEL	= (1U << 0),
 	FREEZE_HOLDER_USERSPACE	= (1U << 1),
 	FREEZE_MAY_NEST		= (1U << 2),
+	FREEZE_EXCL		= (1U << 3),
 };
 
 struct super_operations {
@@ -2295,9 +2298,9 @@ struct super_operations {
 	void (*evict_inode) (struct inode *);
 	void (*put_super) (struct super_block *);
 	int (*sync_fs)(struct super_block *sb, int wait);
-	int (*freeze_super) (struct super_block *, enum freeze_holder who);
+	int (*freeze_super) (struct super_block *, enum freeze_holder who, const void *owner);
 	int (*freeze_fs) (struct super_block *);
-	int (*thaw_super) (struct super_block *, enum freeze_holder who);
+	int (*thaw_super) (struct super_block *, enum freeze_holder who, const void *owner);
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
 	int (*remount_fs) (struct super_block *, int *, char *);
@@ -2705,8 +2708,10 @@ extern int unregister_filesystem(struct file_system_type *);
 extern int vfs_statfs(const struct path *, struct kstatfs *);
 extern int user_statfs(const char __user *, struct kstatfs *);
 extern int fd_statfs(int, struct kstatfs *);
-int freeze_super(struct super_block *super, enum freeze_holder who);
-int thaw_super(struct super_block *super, enum freeze_holder who);
+int freeze_super(struct super_block *super, enum freeze_holder who,
+		 const void *freeze_owner);
+int thaw_super(struct super_block *super, enum freeze_holder who,
+	       const void *freeze_owner);
 extern __printf(2, 3)
 int super_setup_bdi_name(struct super_block *sb, char *fmt, ...);
 extern int super_setup_bdi(struct super_block *sb);
@@ -3518,6 +3523,8 @@ extern void drop_super_exclusive(struct super_block *sb);
 extern void iterate_supers(void (*f)(struct super_block *, void *), void *arg);
 extern void iterate_supers_type(struct file_system_type *,
 			        void (*)(struct super_block *, void *), void *);
+void filesystems_freeze(void);
+void filesystems_thaw(void);
 
 extern int dcache_dir_open(struct inode *, struct file *);
 extern int dcache_dir_close(struct inode *, struct file *);