This is a note to let you know that I've just added the patch titled
fuse: fix possibly missed wake-up after abort
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fuse-fix-possibly-missed-wake-up-after-abort.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7345fc3d0e29b521060d471c9fb2610a4e2c1bde
Author: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Date: Fri Nov 9 15:52:16 2018 +0100
fuse: fix possibly missed wake-up after abort
[ Upstream commit 2d84a2d19b6150c6dbac1e6ebad9c82e4c123772 ]
In current fuse_drop_waiting() implementation it's possible that
fuse_wait_aborted() will not be woken up in the unlikely case that
fuse_abort_conn() + fuse_wait_aborted() runs in between checking
fc->connected and calling atomic_dec(&fc->num_waiting).
Do the atomic_dec_and_test() unconditionally, which also provides the
necessary barrier against reordering with the fc->connected check.
The explicit smp_mb() in fuse_wait_aborted() is not actually needed, since
the spin_unlock() in fuse_abort_conn() provides the necessary RELEASE
barrier after resetting fc->connected. However, this is not a performance
sensitive path, and adding the explicit barrier makes it easier to
document.
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Fixes: b8f95e5d13f5 ("fuse: umount should wait for all requests")
Cc: <stable@xxxxxxxxxxxxxxx> #v4.19
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 770733106d6d4..c934fab444529 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -133,9 +133,13 @@ static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
static void fuse_drop_waiting(struct fuse_conn *fc)
{
- if (fc->connected) {
- atomic_dec(&fc->num_waiting);
- } else if (atomic_dec_and_test(&fc->num_waiting)) {
+ /*
+ * lockess check of fc->connected is okay, because atomic_dec_and_test()
+ * provides a memory barrier mached with the one in fuse_wait_aborted()
+ * to ensure no wake-up is missed.
+ */
+ if (atomic_dec_and_test(&fc->num_waiting) &&
+ !READ_ONCE(fc->connected)) {
/* wake up aborters */
wake_up_all(&fc->blocked_waitq);
}
@@ -2170,6 +2174,8 @@ EXPORT_SYMBOL_GPL(fuse_abort_conn);
void fuse_wait_aborted(struct fuse_conn *fc)
{
+ /* matches implicit memory barrier in fuse_drop_waiting() */
+ smp_mb();
wait_event(fc->blocked_waitq, atomic_read(&fc->num_waiting) == 0);
}
