task #28910367
commit a9bfd9dd3417561d06c81de04f6d6c1e0c9b3d44 upstream

If regular request queue gets full, currently we sleep for a bit and
retrying submission in submitter's context. This assumes submitter is not
holding any spin lock. But this assumption is not true for background
requests. For background requests, we are called with fc->bg_lock held.

This can lead to deadlock where one thread is trying submission with
fc->bg_lock held while request completion thread has called
fuse_request_end() which tries to acquire fc->bg_lock and gets blocked. As
request completion thread gets blocked, it does not make further progress
and that means queue does not get empty and submitter can't submit more
requests.

To solve this issue, retry submission with the help of a worker, instead of
retrying in submitter's context. We already do this for hiprio/forget
requests.
Reported-by: NChirantan Ekbote <chirantan@chromium.org>
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
(cherry picked from commit a9bfd9dd3417561d06c81de04f6d6c1e0c9b3d44)
Signed-off-by: NLiu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>