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Windows: cm_GetNewSCache drop lock to permit change

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In cm_GetNewSCache the entire LRU queue is searched for a
cm_scache_t object that is safe to recycle.  If none are the LRU
queue was immediately searched again without dropping the
cm_scacheLock or taking a pause.  As a result it is quite possible
that a thread about to release a cm_scache_t was blocked from
doing so.

This patchset factors some of the logic a bit differently to
improve readability and adds new log messages to help diagnose
the cause of a problem if no cm_scache_t ever becomes available.

Change-Id: Ica6ebee0ce0456e879ae7188d9c8cdc935a92e5b
Reviewed-on: http://gerrit.openafs.org/7352
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
This commit is contained in:
Jeffrey Altman 2012-05-05 19:11:07 -04:00 committed by Jeffrey Altman
parent dbab42ca72
commit 46c1f1391b
1 changed files with 26 additions and 16 deletions
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42
src/WINNT/afsd/cm_scache.c
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@ -317,22 +317,21 @@ cm_GetNewSCache(afs_uint32 locked)
if (!buf_dirty && !buf_rdr) {
cm_fid_t fid;
afs_uint32 fileType;
int success;
if (!lock_TryWrite(&scp->rw)) {
lock_ObtainWrite(&cm_scacheLock);
if (scp_prev != (cm_scache_t *) osi_QPrev(&scp->q) &&
scp_next != (cm_scache_t *) osi_QNext(&scp->q))
break;
else
continue;
}
success = lock_TryWrite(&scp->rw);
lock_ObtainWrite(&cm_scacheLock);
if (scp_prev != (cm_scache_t *) osi_QPrev(&scp->q) &&
scp_next != (cm_scache_t *) osi_QNext(&scp->q))
{
lock_ReleaseWrite(&scp->rw);
osi_Log1(afsd_logp, "GetNewSCache scp 0x%p; LRU order changed", scp);
if (success)
lock_ReleaseWrite(&scp->rw);
break;
} else if (!success) {
osi_Log1(afsd_logp, "GetNewSCache failed to obtain lock scp 0x%p", scp);
continue;
}
/* Found a likely candidate. Save type and fid in case we succeed */
@ -351,23 +350,34 @@ cm_GetNewSCache(afs_uint32 locked)
goto done;
}
lock_ReleaseWrite(&scp->rw);
} else if (!buf_rdr) {
osi_Log1(afsd_logp, "GetNewSCache dirty buffers scp 0x%p", scp);
lock_ObtainWrite(&cm_scacheLock);
if (scp_prev != (cm_scache_t *) osi_QPrev(&scp->q) &&
scp_next != (cm_scache_t *) osi_QNext(&scp->q))
break;
} else {
osi_Log1(afsd_logp,"GetNewSCache redirector is holding extents scp 0x%p", scp);
if (buf_rdr)
osi_Log1(afsd_logp,"GetNewSCache redirector is holding extents scp 0x%p", scp);
else
osi_Log1(afsd_logp, "GetNewSCache dirty buffers scp 0x%p", scp);
lock_ObtainWrite(&cm_scacheLock);
if (scp_prev != (cm_scache_t *) osi_QPrev(&scp->q) &&
scp_next != (cm_scache_t *) osi_QNext(&scp->q))
{
osi_Log1(afsd_logp, "GetNewSCache scp 0x%p; LRU order changed", scp);
break;
}
}
}
} /* for */
osi_Log2(afsd_logp, "GetNewSCache all scache entries in use (attempt = %d, count = %u)", attempt, count);
if (scp == NULL) {
/*
* The entire LRU queue was walked and no available cm_scache_t was
* found. Drop the cm_scacheLock and sleep for a moment to give a
* chance for cm_scache_t objects to be released.
*/
lock_ReleaseWrite(&cm_scacheLock);
Sleep(50);
lock_ObtainWrite(&cm_scacheLock);
}
}
/* FAILURE */
scp = NULL;