ceph: drop mdsc->mutex before decoding the MDS reply

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handle_reply() held `mdsc->mutex` across parse_reply_info(),
i.e. across the full decode of the reply message.  For large replies
(a big readdir allocates and parses many dir_entries), this can take a
while and blocks ceph_mdsc_submit_request() calls meanwhile.

The decode does not need `mdsc->mutex`: parse_reply_info() mostly
fills the request's `r_reply_info`.  Create replies may also add
delegated inode numbers to the session xarray, but that xarray is
protected by its own lock and is not serialized by `mdsc->mutex`
today.  By the time we reach parse_reply_info(), all
`mdsc->mutex`-protected state has already been updated under the lock
(the request has either been unregistered (safe reply) or added to the
session's unsafe list (unsafe reply)) and the request is pinned by the
reference taken in lookup_get_request().

Drop `mdsc->mutex` before calling parse_reply_info() so reply decoding
no longer blocks request submission.  This only widens the existing
unlocked window that already covers the heavier ceph_fill_trace() /
ceph_readdir_prepopulate() processing, so no new races are introduced.

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Reviewed-by: Xiubo Li <xiubo.li@clyso.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

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Max Kellermann 2026-07-08 22:40:22 +02:00 • committed by Ilya Dryomov

parent ee611a7509

commit 1319b97dfe

1 changed files with 7 additions and 1 deletions

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fs/ceph/mds_client.c

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