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Message-ID: <20250731220024.702621-4-surenb@google.com>
Date: Thu, 31 Jul 2025 15:00:24 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, david@...hat.com,
vbabka@...e.cz, peterx@...hat.com, jannh@...gle.com, hannes@...xchg.org,
mhocko@...nel.org, paulmck@...nel.org, shuah@...nel.org, adobriyan@...il.com,
brauner@...nel.org, josef@...icpanda.com, yebin10@...wei.com,
linux@...ssschuh.net, willy@...radead.org, osalvador@...e.de,
andrii@...nel.org, ryan.roberts@....com, christophe.leroy@...roup.eu,
tjmercier@...gle.com, kaleshsingh@...gle.com, aha310510@...il.com,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kselftest@...r.kernel.org, surenb@...gle.com
Subject: [PATCH 3/3] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under
per-vma locks
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.
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
fs/proc/task_mmu.c | 81 +++++++++++++++++++++++++++++++++++++---------
1 file changed, 65 insertions(+), 16 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 509fa162760a..b504b798e8fe 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -517,28 +517,78 @@ 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_query_data *query)
{
- return mmap_read_lock_killable(mm);
+ query->locked_vma = NULL;
+ query->mmap_locked = false;
+
+ return 0;
}
-static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma)
+static void query_vma_teardown(struct proc_maps_query_data *query)
{
- mmap_read_unlock(mm);
+ if (query->mmap_locked)
+ mmap_read_unlock(query->mm);
+ else
+ unlock_vma(query);
}
-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_query_data *query,
+ unsigned long addr)
{
- return find_vma(mm, addr);
+ struct vm_area_struct *vma;
+ struct vma_iterator vmi;
+
+ unlock_vma(query);
+ rcu_read_lock();
+ vma_iter_init(&vmi, query->mm, addr);
+ vma = lock_next_vma(query->mm, &vmi, addr);
+ rcu_read_unlock();
+
+ if (!IS_ERR_OR_NULL(vma)) {
+ query->locked_vma = vma;
+ } else if (PTR_ERR(vma) == -EAGAIN) {
+ /* Fallback to mmap_lock on vma->vm_refcnt overflow */
+ mmap_read_lock(query->mm);
+ vma = find_vma(query->mm, addr);
+ query->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_query_data *query)
+{
+ return mmap_read_lock_killable(query->mm);
+}
+
+static void query_vma_teardown(struct proc_maps_query_data *query)
+{
+ mmap_read_unlock(query->mm);
+}
+
+static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_query_data *query,
+ unsigned long addr)
+{
+ return find_vma(query->mm, addr);
+}
+
+#endif /* CONFIG_PER_VMA_LOCK */
+
+static struct vm_area_struct *query_matching_vma(struct proc_maps_query_data *query,
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(query, addr);
+ if (IS_ERR(vma))
+ return vma;
+
if (!vma)
goto no_vma;
@@ -579,11 +629,11 @@ 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_query_data query = { .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;
@@ -610,17 +660,16 @@ 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->query.mm;
if (!mm || !mmget_not_zero(mm))
return -ESRCH;
- err = query_vma_setup(mm);
+ err = query_vma_setup(&query);
if (err) {
mmput(mm);
return err;
}
- vma = query_matching_vma(mm, karg.query_addr, karg.query_flags);
+ vma = query_matching_vma(&query, karg.query_addr, karg.query_flags);
if (IS_ERR(vma)) {
err = PTR_ERR(vma);
vma = NULL;
@@ -705,7 +754,7 @@ 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(&query);
mmput(mm);
if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr),
@@ -725,7 +774,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
return 0;
out:
- query_vma_teardown(mm, vma);
+ query_vma_teardown(&query);
mmput(mm);
kfree(name_buf);
return err;
@@ -738,7 +787,7 @@ 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);
+ return do_procmap_query(priv->query.mm, (void __user *)arg);
default:
return -ENOIOCTLCMD;
}
--
2.50.1.565.gc32cd1483b-goog
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