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fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks

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Utilize per-vma locks to stabilize vma after lookup without taking
mmap_lock during PROCMAP_QUERY ioctl execution. If vma lock is
contended, we fall back to mmap_lock but take it only momentarily
to lock the vma and release the mmap_lock. In a very unlikely case
of vm_refcnt overflow, this fall back path will fail and ioctl is
done under mmap_lock protection.

This change is designed to reduce mmap_lock contention and prevent
PROCMAP_QUERY ioctl calls from blocking address space updates.

Link: https://lkml.kernel.org/r/20250808152850.2580887-4-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Ye Bin <yebin10@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Suren Baghdasaryan 2025-08-08 08:28:49 -07:00 committed by Andrew Morton
parent ee737a5a10
commit d9d1c2d817
1 changed files with 85 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

103
fs/proc/task_mmu.c
View File

@ -132,6 +132,12 @@ static void release_task_mempolicy(struct proc_maps_private *priv)
#ifdef CONFIG_PER_VMA_LOCK
static void reset_lock_ctx(struct proc_maps_locking_ctx *lock_ctx)
{
lock_ctx->locked_vma = NULL;
lock_ctx->mmap_locked = false;
}
static void unlock_ctx_vma(struct proc_maps_locking_ctx *lock_ctx)
{
if (lock_ctx->locked_vma) {
@ -157,8 +163,7 @@ static inline bool lock_vma_range(struct seq_file *m,
lock_ctx->mmap_locked = true;
} else {
rcu_read_lock();
lock_ctx->locked_vma = NULL;
lock_ctx->mmap_locked = false;
reset_lock_ctx(lock_ctx);
}
return true;
@ -522,28 +527,90 @@ static int pid_maps_open(struct inode *inode, struct file *file)
PROCMAP_QUERY_VMA_FLAGS \
)
static int query_vma_setup(struct mm_struct *mm)
#ifdef CONFIG_PER_VMA_LOCK
static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx)
{
return mmap_read_lock_killable(mm);
reset_lock_ctx(lock_ctx);
return 0;
}
static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma)
static void query_vma_teardown(struct proc_maps_locking_ctx *lock_ctx)
{
mmap_read_unlock(mm);
if (lock_ctx->mmap_locked) {
mmap_read_unlock(lock_ctx->mm);
lock_ctx->mmap_locked = false;
} else {
unlock_ctx_vma(lock_ctx);
}
}
static struct vm_area_struct *query_vma_find_by_addr(struct mm_struct *mm, unsigned long addr)
static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ctx *lock_ctx,
unsigned long addr)
{
return find_vma(mm, addr);
struct mm_struct *mm = lock_ctx->mm;
struct vm_area_struct *vma;
struct vma_iterator vmi;
if (lock_ctx->mmap_locked)
return find_vma(mm, addr);
/* Unlock previously locked VMA and find the next one under RCU */
unlock_ctx_vma(lock_ctx);
rcu_read_lock();
vma_iter_init(&vmi, mm, addr);
vma = lock_next_vma(mm, &vmi, addr);
rcu_read_unlock();
if (!vma)
return NULL;
if (!IS_ERR(vma)) {
lock_ctx->locked_vma = vma;
return vma;
}
if (PTR_ERR(vma) == -EAGAIN) {
/* Fallback to mmap_lock on vma->vm_refcnt overflow */
mmap_read_lock(mm);
vma = find_vma(mm, addr);
lock_ctx->mmap_locked = true;
}
return vma;
}
static struct vm_area_struct *query_matching_vma(struct mm_struct *mm,
#else /* CONFIG_PER_VMA_LOCK */
static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx)
{
return mmap_read_lock_killable(lock_ctx->mm);
}
static void query_vma_teardown(struct proc_maps_locking_ctx *lock_ctx)
{
mmap_read_unlock(lock_ctx->mm);
}
static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ctx *lock_ctx,
unsigned long addr)
{
return find_vma(lock_ctx->mm, addr);
}
#endif /* CONFIG_PER_VMA_LOCK */
static struct vm_area_struct *query_matching_vma(struct proc_maps_locking_ctx *lock_ctx,
unsigned long addr, u32 flags)
{
struct vm_area_struct *vma;
next_vma:
vma = query_vma_find_by_addr(mm, addr);
vma = query_vma_find_by_addr(lock_ctx, addr);
if (IS_ERR(vma))
return vma;
if (!vma)
goto no_vma;
@ -584,11 +651,11 @@ static struct vm_area_struct *query_matching_vma(struct mm_struct *mm,
return ERR_PTR(-ENOENT);
}
static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
static int do_procmap_query(struct mm_struct *mm, void __user *uarg)
{
struct proc_maps_locking_ctx lock_ctx = { .mm = mm };
struct procmap_query karg;
struct vm_area_struct *vma;
struct mm_struct *mm;
const char *name = NULL;
char build_id_buf[BUILD_ID_SIZE_MAX], *name_buf = NULL;
__u64 usize;
@ -615,17 +682,16 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
if (!!karg.build_id_size != !!karg.build_id_addr)
return -EINVAL;
mm = priv->lock_ctx.mm;
if (!mm || !mmget_not_zero(mm))
return -ESRCH;
err = query_vma_setup(mm);
err = query_vma_setup(&lock_ctx);
if (err) {
mmput(mm);
return err;
}
vma = query_matching_vma(mm, karg.query_addr, karg.query_flags);
vma = query_matching_vma(&lock_ctx, karg.query_addr, karg.query_flags);
if (IS_ERR(vma)) {
err = PTR_ERR(vma);
vma = NULL;
@ -710,7 +776,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
}
/* unlock vma or mmap_lock, and put mm_struct before copying data to user */
query_vma_teardown(mm, vma);
query_vma_teardown(&lock_ctx);
mmput(mm);
if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr),
@ -730,7 +796,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
return 0;
out:
query_vma_teardown(mm, vma);
query_vma_teardown(&lock_ctx);
mmput(mm);
kfree(name_buf);
return err;
@ -743,7 +809,8 @@ static long procfs_procmap_ioctl(struct file *file, unsigned int cmd, unsigned l
switch (cmd) {
case PROCMAP_QUERY:
return do_procmap_query(priv, (void __user *)arg);
/* priv->lock_ctx.mm is set during file open operation */
return do_procmap_query(priv->lock_ctx.mm, (void __user *)arg);
default:
return -ENOIOCTLCMD;
}