git: kernel - Fix rare vref() assertion

[Matthew Dillon]

commit 74272eaf4d2c0a0f58092e8f8035e66d1e0c3ce4
Author: Matthew Dillon <***@apollo.backplane.com>
Date: Sat Dec 8 14:34:51 2018 -0800

kernel - Fix rare vref() assertion

* The VREF_TERMINATE flag gets cleared when a vnode is reactivated.
However, concurrent LK_SHARED locks on vnodes can race the v_state
test. Thus the code cannot assume that VREF_TERMINATE has been cleared
when v_state is VS_ACTIVE.

To avoid the race, we simply unconditionally clear VREF_TERMINATE on
a successful vget().

* Could be reproduced by running blogbench and synth together, both of
which generate extreme filesystem-intensive loads.

Summary of changes:
sys/kern/vfs_lock.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/74272eaf4d2c0a0f58092e8f8035e66d1e0c3ce4