[lvc-project] [PATCH 19/19] gfs2: Remove unnecessary sd_jdesc NULL check in gfs2_log_flush

[Nikolai Kuznetsov]

Commit 35264909e9d1 ("gfs2: Fix NULL pointer dereference in
gfs2_log_flush") added an explicit NULL check for sd_jdesc
to avoid a race with unmount.

Note that the explicit NULL check alone was insufficient, as other
functions e.g. log_distance() still dereference sd_jdesc.

However, gfs2_log_flush() checks for SDF_JOURNAL_LIVE bit and bails
out if it's not set. During unmount this bit is cleared in final
shutdown flush which is called in gfs2_make_fs_ro().

Filesystem becomes RO firstly and only then sd_jdesc is assigned
NULL in gfs2_jindex_free(), so the race is not possible. The
explicit check is redundant, remove it.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 35264909e9d1 ("gfs2: Fix NULL pointer dereference in gfs2_log_flush")
Fixes: 74b4dbb94606 ("gfs2: prevent NULL pointer dereference during unmount")
Signed-off-by: Nikolai Kuznetsov <niku.csmsu at yandex.ru>
---
 fs/gfs2/log.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 78bba8cc10b8..0b91f3e0928a 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -467,7 +467,7 @@ 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, !sdp->sd_jdesc ||
+	gfs2_assert_withdraw(sdp,
 			atomic_read(&sdp->sd_log_blks_free) <=
 			sdp->sd_jdesc->jd_blocks);
 	if (atomic_read(&sdp->sd_log_blks_needed))
@@ -1137,8 +1137,9 @@ static void __gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl,
 	lops_before_commit(sdp, tr);
 	if (gfs2_withdrawn(sdp))
 		goto out_withdraw;
-	if (sdp->sd_jdesc)
-		gfs2_log_submit_write(&sdp->sd_jdesc->jd_log_bio);
+
+	gfs2_log_submit_write(&sdp->sd_jdesc->jd_log_bio);
+
 	if (gfs2_withdrawn(sdp))
 		goto out_withdraw;
 
-- 
2.43.0