K 10
svn:author
V 5
markj
K 8
svn:date
V 27
2019-07-24T23:04:59.100991Z
K 7
svn:log
V 636
Fix the turnstile_lock() KPI.

turnstile_{lock,unlock}() were added for use in epoch.  turnstile_lock()
returned NULL to indicate that the calling thread had lost a race and
the turnstile was no longer associated with the given lock, or the lock
owner.  However, reader-writer locks may not have a designated owner,
in which case turnstile_lock() would return NULL and
epoch_block_handler_preempt() would leak spinlocks as a result.

Apply a minimal fix: return the lock owner as a separate return value.

Reviewed by:	kib
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D21048

END