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fuse: fix possibly missed wake-up after abort
commit2d84a2d19b
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:b8f95e5d13
("fuse: umount should wait for all requests") Cc: <stable@vger.kernel.org> #v4.19 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 9 additions and 3 deletions
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@ -129,9 +129,13 @@ static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
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static void fuse_drop_waiting(struct fuse_conn *fc)
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{
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if (fc->connected) {
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atomic_dec(&fc->num_waiting);
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} else if (atomic_dec_and_test(&fc->num_waiting)) {
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/*
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* lockess check of fc->connected is okay, because atomic_dec_and_test()
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* provides a memory barrier mached with the one in fuse_wait_aborted()
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* to ensure no wake-up is missed.
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*/
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if (atomic_dec_and_test(&fc->num_waiting) &&
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!READ_ONCE(fc->connected)) {
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/* wake up aborters */
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wake_up_all(&fc->blocked_waitq);
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}
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@ -2167,6 +2171,8 @@ EXPORT_SYMBOL_GPL(fuse_abort_conn);
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void fuse_wait_aborted(struct fuse_conn *fc)
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{
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/* matches implicit memory barrier in fuse_drop_waiting() */
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smp_mb();
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wait_event(fc->blocked_waitq, atomic_read(&fc->num_waiting) == 0);
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}
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