diff options
| author | Miklos Szeredi <mszeredi@redhat.com> | 2018-11-09 15:52:16 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-05-02 17:20:51 +0200 |
| commit | d2a2ac28ef55f2cc88e9ff541e37d3f67446397a (patch) | |
| tree | 6abf45f06119346157f25ddc187ca2b4a1474d71 | |
| parent | ff82cd319a9244d230f291fa8613ed2f098d18b3 (diff) | |
fuse: fix possibly missed wake-up after abort
commit 2d84a2d19b6150c6dbac1e6ebad9c82e4c123772 upstream.
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@redhat.com>
Fixes: b8f95e5d13f5 ("fuse: umount should wait for all requests")
Cc: <stable@vger.kernel.org> #v4.19
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/fuse/dev.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 16891f5364af..8142f6bf3d31 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -145,9 +145,13 @@ 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); } @@ -2222,6 +2226,8 @@ 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); } |