From f67950b2887fa10df50c4317a1fe98a65bc6875b Mon Sep 17 00:00:00 2001 From: David Carlier Date: Sat, 18 Apr 2026 16:22:50 +0100 Subject: [PATCH 1/2] eventfs: Use list_add_tail_rcu() for SRCU-protected children list Commit d2603279c7d6 ("eventfs: Use list_del_rcu() for SRCU protected list variable") converted the removal side to pair with the list_for_each_entry_srcu() walker in eventfs_iterate(). The insertion in eventfs_create_dir() was left as a plain list_add_tail(), which on weakly-ordered architectures can expose a new entry to the SRCU reader before its list pointers and fields are observable. Use list_add_tail_rcu() so the publication pairs with the existing list_del_rcu() and list_for_each_entry_srcu(). Fixes: 43aa6f97c2d0 ("eventfs: Get rid of dentry pointers without refcounts") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260418152251.199343-1-devnexen@gmail.com Signed-off-by: David Carlier Signed-off-by: Steven Rostedt --- fs/tracefs/event_inode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 81df94038f2e..8dd554508828 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -706,7 +706,7 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode scoped_guard(mutex, &eventfs_mutex) { if (!parent->is_freed) - list_add_tail(&ei->list, &parent->children); + list_add_tail_rcu(&ei->list, &parent->children); } /* Was the parent freed? */ if (list_empty(&ei->list)) { From 07004a8c4b572171934390148ee48c4175c77eed Mon Sep 17 00:00:00 2001 From: David Carlier Date: Sat, 18 Apr 2026 20:17:37 +0100 Subject: [PATCH 2/2] eventfs: Hold eventfs_mutex and SRCU when remount walks events Commit 340f0c7067a9 ("eventfs: Update all the eventfs_inodes from the events descriptor") had eventfs_set_attrs() recurse through ei->children on remount. The walk only holds the rcu_read_lock() taken by tracefs_apply_options() over tracefs_inodes, which is wrong: - list_for_each_entry over ei->children races with the list_del_rcu() in eventfs_remove_rec() -- LIST_POISON1 deref, same shape as d2603279c7d6. - eventfs_inodes are freed via call_srcu(&eventfs_srcu, ...). rcu_read_lock() does not extend an SRCU grace period, so ti->private can be reclaimed under the walk. - The writes to ei->attr race with eventfs_set_attr(), which holds eventfs_mutex. Reproducer: while :; do mount -o remount,uid=$((RANDOM%1000)) /sys/kernel/tracing; done & while :; do echo "p:kp submit_bio" > /sys/kernel/tracing/kprobe_events echo > /sys/kernel/tracing/kprobe_events done Wrap the events portion of tracefs_apply_options() in eventfs_remount_lock()/_unlock() that take eventfs_mutex and srcu_read_lock(&eventfs_srcu). eventfs_set_attrs() doesn't sleep so the nested rcu_read_lock() is fine; lockdep_assert_held() pins the contract. Comment in tracefs_drop_inode() said "RCU cycle" -- it is SRCU. Fixes: 340f0c7067a9 ("eventfs: Update all the eventfs_inodes from the events descriptor") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260418191737.10289-1-devnexen@gmail.com Signed-off-by: David Carlier Signed-off-by: Steven Rostedt --- fs/tracefs/event_inode.c | 14 ++++++++++++++ fs/tracefs/inode.c | 5 ++++- fs/tracefs/internal.h | 3 +++ 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 8dd554508828..26b6453de30e 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -244,6 +244,8 @@ static void eventfs_set_attrs(struct eventfs_inode *ei, bool update_uid, kuid_t { struct eventfs_inode *ei_child; + lockdep_assert_held(&eventfs_mutex); + /* Update events// */ if (WARN_ON_ONCE(level > 3)) return; @@ -886,3 +888,15 @@ void eventfs_remove_events_dir(struct eventfs_inode *ei) d_invalidate(dentry); d_make_discardable(dentry); } + +int eventfs_remount_lock(void) +{ + mutex_lock(&eventfs_mutex); + return srcu_read_lock(&eventfs_srcu); +} + +void eventfs_remount_unlock(int srcu_idx) +{ + srcu_read_unlock(&eventfs_srcu, srcu_idx); + mutex_unlock(&eventfs_mutex); +} diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 5602baf980f6..1e8a78c5e996 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -313,6 +313,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount) struct inode *inode = d_inode(sb->s_root); struct tracefs_inode *ti; bool update_uid, update_gid; + int srcu_idx; umode_t tmp_mode; /* @@ -337,6 +338,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount) update_uid = fsi->opts & BIT(Opt_uid); update_gid = fsi->opts & BIT(Opt_gid); + srcu_idx = eventfs_remount_lock(); rcu_read_lock(); list_for_each_entry_rcu(ti, &tracefs_inodes, list) { if (update_uid) { @@ -358,6 +360,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount) eventfs_remount(ti, update_uid, update_gid); } rcu_read_unlock(); + eventfs_remount_unlock(srcu_idx); } return 0; @@ -403,7 +406,7 @@ static int tracefs_drop_inode(struct inode *inode) * This inode is being freed and cannot be used for * eventfs. Clear the flag so that it doesn't call into * eventfs during the remount flag updates. The eventfs_inode - * gets freed after an RCU cycle, so the content will still + * gets freed after an SRCU cycle, so the content will still * be safe if the iteration is going on now. */ ti->flags &= ~TRACEFS_EVENT_INODE; diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index d83c2a25f288..a4a7f8431aff 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h @@ -76,4 +76,7 @@ struct inode *tracefs_get_inode(struct super_block *sb); void eventfs_remount(struct tracefs_inode *ti, bool update_uid, bool update_gid); void eventfs_d_release(struct dentry *dentry); +int eventfs_remount_lock(void); +void eventfs_remount_unlock(int srcu_idx); + #endif /* _TRACEFS_INTERNAL_H */