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authorAl Viro <viro@zeniv.linux.org.uk>2023-09-30 03:24:34 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2024-02-25 10:10:31 +0300
commit275655d3207b9e65d1561bf21c06a622d9ec1d43 (patch)
treea57f17b452a230ede597dc2d9bbed33e597e99f0 /fs/afs/file.c
parentaf072cf683acd2307e02378cfcf2502c49d2e127 (diff)
downloadlinux-275655d3207b9e65d1561bf21c06a622d9ec1d43.tar.xz
afs: fix __afs_break_callback() / afs_drop_open_mmap() race
In __afs_break_callback() we might check ->cb_nr_mmap and if it's non-zero do queue_work(&vnode->cb_work). In afs_drop_open_mmap() we decrement ->cb_nr_mmap and do flush_work(&vnode->cb_work) if it reaches zero. The trouble is, there's nothing to prevent __afs_break_callback() from seeing ->cb_nr_mmap before the decrement and do queue_work() after both the decrement and flush_work(). If that happens, we might be in trouble - vnode might get freed before the queued work runs. __afs_break_callback() is always done under ->cb_lock, so let's make sure that ->cb_nr_mmap can change from non-zero to zero while holding ->cb_lock (the spinlock component of it - it's a seqlock and we don't need to mess with the counter). Acked-by: Christian Brauner <brauner@kernel.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/afs/file.c')
-rw-r--r--fs/afs/file.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/fs/afs/file.c b/fs/afs/file.c
index 3d33b221d9ca..ef2cc8f565d2 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -417,13 +417,17 @@ static void afs_add_open_mmap(struct afs_vnode *vnode)
static void afs_drop_open_mmap(struct afs_vnode *vnode)
{
- if (!atomic_dec_and_test(&vnode->cb_nr_mmap))
+ if (atomic_add_unless(&vnode->cb_nr_mmap, -1, 1))
return;
down_write(&vnode->volume->open_mmaps_lock);
- if (atomic_read(&vnode->cb_nr_mmap) == 0)
+ read_seqlock_excl(&vnode->cb_lock);
+ // the only place where ->cb_nr_mmap may hit 0
+ // see __afs_break_callback() for the other side...
+ if (atomic_dec_and_test(&vnode->cb_nr_mmap))
list_del_init(&vnode->cb_mmap_link);
+ read_sequnlock_excl(&vnode->cb_lock);
up_write(&vnode->volume->open_mmaps_lock);
flush_work(&vnode->cb_work);