svn commit: r324689 - head/sys/dev/iscsi
Andriy Gapon
avg at FreeBSD.org
Tue Oct 17 15:39:40 UTC 2017
Author: avg
Date: Tue Oct 17 15:39:38 2017
New Revision: 324689
URL: https://svnweb.freebsd.org/changeset/base/324689
Log:
iscsi: do not hold the global lock while tearing down a session
It should be sufficient to hold the lock just for removing the session
from the session list. Everything else should be covered by the session
specific lock.
On top of that, at present we can get a deadlock caused by waiting on
the CAM SIM reference count while holding the global lock. A specific
scenario involving ZFS is this:
- concurrent termination of two sessions, S1 and S2
- session S1 completed all I/Os and sleeps in CAM waiting for device
close by ZFS;
- session S2 is also dead now, but can not forcefully complete
outstanding requests by calling iscsi_session_cleanup() from
iscsi_maintenance_thread_terminate(), since it can't get the same
global sc_lock;
- as soon as there are unfinished requests, ZFS can not do
spa_config_enter() as writer, and so can not close the device for
session S1;
- deadlock.
Reported by: Ben RUBSON <ben.rubson at gmail.com>
Tested by: Ben RUBSON <ben.rubson at gmail.com>
Reviewed by: mav, trasz
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D12652
Modified:
head/sys/dev/iscsi/iscsi.c
Modified: head/sys/dev/iscsi/iscsi.c
==============================================================================
--- head/sys/dev/iscsi/iscsi.c Tue Oct 17 14:37:12 2017 (r324688)
+++ head/sys/dev/iscsi/iscsi.c Tue Oct 17 15:39:38 2017 (r324689)
@@ -434,6 +434,8 @@ iscsi_maintenance_thread_terminate(struct iscsi_sessio
sc = is->is_softc;
sx_xlock(&sc->sc_lock);
+ TAILQ_REMOVE(&sc->sc_sessions, is, is_next);
+ sx_xunlock(&sc->sc_lock);
icl_conn_close(is->is_conn);
callout_drain(&is->is_callout);
@@ -465,8 +467,6 @@ iscsi_maintenance_thread_terminate(struct iscsi_sessio
#ifdef ICL_KERNEL_PROXY
cv_destroy(&is->is_login_cv);
#endif
- TAILQ_REMOVE(&sc->sc_sessions, is, is_next);
- sx_xunlock(&sc->sc_lock);
ISCSI_SESSION_DEBUG(is, "terminated");
free(is, M_ISCSI);
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