gfs2: Fix potential glock use-after-free on unmount

When a DLM lockspace is released and there ares still locks in that
lockspace, DLM will unlock those locks automatically.  Commit
fb6791d100d1b started exploiting this behavior to speed up filesystem
unmount: gfs2 would simply free glocks it didn't want to unlock and then
release the lockspace.  This didn't take the bast callbacks for
asynchronous lock contention notifications into account, which remain
active until until a lock is unlocked or its lockspace is released.

To prevent those callbacks from accessing deallocated objects, put the
glocks that should not be unlocked on the sd_dead_glocks list, release
the lockspace, and only then free those glocks.

As an additional measure, ignore unexpected ast and bast callbacks if
the receiving glock is dead.

Fixes: fb6791d100d1b ("GFS2: skip dlm_unlock calls in unmount")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Cc: David Teigland <teigland@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index 2c697674a86f..19aef6d53267 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -252,6 +252,7 @@ void gfs2_gl_dq_holders(struct gfs2_sbd *sdp);
 void gfs2_glock_thaw(struct gfs2_sbd *sdp);
 void gfs2_glock_add_to_lru(struct gfs2_glock *gl);
 void gfs2_glock_free(struct gfs2_glock *gl);
+void gfs2_glock_free_later(struct gfs2_glock *gl);
 
 int __init gfs2_glock_init(void);
 void gfs2_glock_exit(void);