[PATCH 18/18] gfs2: prevent NULL pointer dereference during unmount

When flushing out outstanding glock work during an unmount, gfs2_log_flush()
can be called when sdp->sd_jdesc has already been deallocated and sdp->sd_jdesc
is NULL.  Commit 35264909e9d1 ("gfs2: Fix NULL pointer dereference in
gfs2_log_flush") added a check for that to gfs2_log_flush() itself, but it
missed the sdp->sd_jdesc dereference in gfs2_log_release().  Fix that.

Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]/
Fixes: 35264909e9d1 ("gfs2: Fix NULL pointer dereference in gfs2_log_flush")
Signed-off-by: Andreas Gruenbacher <[email protected]>
---
 fs/gfs2/log.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 3a01d4e7667a..78bba8cc10b8 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -467,8 +467,9 @@ void gfs2_log_release(struct gfs2_sbd *sdp, unsigned int blks)
 {
 	atomic_add(blks, &sdp->sd_log_blks_free);
 	trace_gfs2_log_blocks(sdp, blks);
-	gfs2_assert_withdraw(sdp, atomic_read(&sdp->sd_log_blks_free) <=
-				  sdp->sd_jdesc->jd_blocks);
+	gfs2_assert_withdraw(sdp, !sdp->sd_jdesc ||
+			atomic_read(&sdp->sd_log_blks_free) <=
+			sdp->sd_jdesc->jd_blocks);
 	if (atomic_read(&sdp->sd_log_blks_needed))
 		wake_up(&sdp->sd_log_waitq);
 }
-- 
2.53.0