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Remote and local adv lock servers might de-synchronize (the added comment

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explains the plausible scenario), resulting in EDEADLK returned on the
local registration attempt.  Handle this by re-trying the local op [1].

On unmount, local registration abort is indicated as EINTR, abort the nlm
call as well.

Reported and tested by:	pho
Suggested and reviewed by:	dfr (previous version, [1])
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Approved by:	re (delphij)
This commit is contained in:
Konstantin Belousov 2016-06-19 18:32:35 +00:00
parent e37dfd3d2b
commit 04b49c9154
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=302020
1 changed files with 31 additions and 1 deletions
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32
sys/nlm/nlm_advlock.c
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@ -713,7 +713,37 @@ nlm_record_lock(struct vnode *vp, int op, struct flock *fl,
newfl.l_pid = svid;
newfl.l_sysid = NLM_SYSID_CLIENT | sysid;
error = lf_advlockasync(&a, &vp->v_lockf, size);
for (;;) {
error = lf_advlockasync(&a, &vp->v_lockf, size);
if (error == EDEADLK) {
/*
* Locks are associated with the processes and
* not with threads. Suppose we have two
* threads A1 A2 in one process, A1 locked
* file f1, A2 is locking file f2, and A1 is
* unlocking f1. Then remote server may
* already unlocked f1, while local still not
* yet scheduled A1 to make the call to local
* advlock manager. The process B owns lock on
* f2 and issued the lock on f1. Remote would
* grant B the request on f1, but local would
* return EDEADLK.
*/
pause("nlmdlk", 1);
/* XXXKIB allow suspend */
} else if (error == EINTR) {
/*
* lf_purgelocks() might wake up the lock
* waiter and removed our lock graph edges.
* There is no sense in re-trying recording
* the lock to the local manager after
* reclaim.
*/
error = 0;
break;
} else
break;
}
KASSERT(error == 0 || error == ENOENT,
("Failed to register NFS lock locally - error=%d", error));
}