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module: freebsd: avoid a taking a destroyed lock in zfs_zevent bits 

At shutdown time, we drain all of the zevents and set the
ZEVENT_SHUTDOWN flag.  On FreeBSD, we may end up calling
zfs_zevent_destroy() after the zevent_lock has been destroyed while
the sysevent thread is winding down; we observe ESHUTDOWN, then back
out.

Events have already been drained, so just inline the kmem_free call in
sysevent_worker() to avoid the race, and document the assumption that
zfs_zevent_destroy doesn't do anything else useful at that point.

This fixes a panic that can occur at module unload time.

Reviewed-by: Ryan Moeller <freqlabs@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Closes #13220
This commit is contained in:
Kyle Evans 2022-03-17 12:14:00 -05:00 committed by GitHub
parent 6ef00196db
commit bee314a798
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1 changed files with 11 additions and 1 deletions
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12
module/os/freebsd/spl/spl_sysevent.c
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@ -250,7 +250,17 @@ sysevent_worker(void *arg __unused)
nvlist_free(event);
}
}
zfs_zevent_destroy(ze);
/*
* We avoid zfs_zevent_destroy() here because we're otherwise racing
* against fm_fini() destroying the zevent_lock. zfs_zevent_destroy()
* will currently only clear `ze->ze_zevent` from an event list then
* free `ze`, so just inline the free() here -- events have already
* been drained.
*/
VERIFY3P(ze->ze_zevent, ==, NULL);
kmem_free(ze, sizeof (zfs_zevent_t));
kthread_exit();
}