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afs: fix afs_xserver deadlock in afsdb refresh

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When setting up a new volume, the cache manager calls afs_GetServer() to
setup the server object for each fileserver associated with the volume.
The afs_GetServer() function locks afs_xserver and then, among other
things, calls afs_GetCell() to lookup the cell info by cell number.

When the cache manager is running in afsdb mode, afs_GetCell() will
attempt to refresh the cell info if the time-to-live has been exceeded
since the last call to afs_GetCell(). During this refresh the AFSDB
calls afs_GetServer() to update the vlserver information. The afsdb
handler thread and the thread processing the volume setup become
deadlocked since the afs_xserver lock is already held at this point.

This bug will manifest when the DNS SRV record TTL is smaller than the
time the fileservers respond to the GetCapabilities RPC within
afs_GetServer() and there are multiple read-only servers for a volume.

Avoid the deadlock by using the afs_GetCellStale() variant within
afs_GetServer(). This variant returns the memory resident cell info
without the afsdb upcall and the subsequent afs_GetServer() call.

Change-Id: Iad57870f84c5e542a5ee20f00ea03b3fc87683a1
Reviewed-on: https://gerrit.openafs.org/12652
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
This commit is contained in:
Michael Meffie 2017-07-07 11:11:12 -04:00 committed by Benjamin Kaduk
parent a6ad67485b
commit 030a9849e2
1 changed files with 4 additions and 2 deletions
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6
src/afs/afs_server.c
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@ -1675,7 +1675,8 @@ afs_GetServer(afs_uint32 *aserverp, afs_int32 nservers, afs_int32 acell,
newts->flags |= SRVR_MULTIHOMED; newts->flags |= SRVR_MULTIHOMED;
} }
if (acell) if (acell)
newts->cell = afs_GetCell(acell, 0); /* Use the afs_GetCellStale variant to avoid afs_GetServer recursion. */
newts->cell = afs_GetCellStale(acell, 0);
/* For each IP address we are registering */ /* For each IP address we are registering */
for (k = 0; k < nservers; k++) { for (k = 0; k < nservers; k++) {
@ -1764,7 +1765,8 @@ afs_GetServer(afs_uint32 *aserverp, afs_int32 nservers, afs_int32 acell,
afs_servers[iphash] = orphts; afs_servers[iphash] = orphts;
if (acell) if (acell)
orphts->cell = afs_GetCell(acell, 0); /* Use the afs_GetCellStale variant to avoid afs_GetServer recursion. */
orphts->cell = afs_GetCellStale(acell, 0);
} }
/* Hang the srvAddr struct off of the server structure. The server /* Hang the srvAddr struct off of the server structure. The server