[Cluster-devel] [GFS2 PATCH] gfs2: Panic when an io error occurs writing to the journal

[Bob Peterson]

Hi,

Before this patch, gfs2 would try to withdraw when it encountered
io errors writing to its journal. That's incorrect behavior
because if it can't write to the journal, it cannot write revokes
for the metadata it sends down. A withdraw will cause gfs2 to
unmount the file system from dlm, which is a controlled shutdown,
but the io error means it cannot write the UNMOUNT log header
to the journal. The controlled shutdown will cause dlm to release
all its locks, allowing other nodes to update the metadata.
When the node rejoins the cluster and sees no UNMOUNT log header
it will see the journal is dirty and replay it, but after the
other nodes may have changed the metadata, thus corrupting the
file system.

If we get an io error writing to the journal, the only correct
thing to do is to kernel panic. That will force dlm to go through
its full recovery process on the other cluster nodes, freeze all
locks, and make sure the journal is replayed by a node in the
cluster before any other nodes get the affected locks and try to
modify the metadata in the unfinished portion of the journal.

This patch changes the behavior so that io errors encountered
in the journals cause an immediate kernel panic with a message.
However, quota update errors are still allowed to withdraw as
before.

Signed-off-by: Bob Peterson <rpeterso at redhat.com>
---
 fs/gfs2/lops.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 94dcab655bc0..44b85f7675d4 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -209,11 +209,9 @@ static void gfs2_end_log_write(struct bio *bio)
 	struct page *page;
 	int i;
 
-	if (bio->bi_status) {
-		fs_err(sdp, "Error %d writing to journal, jid=%u\n",
-		       bio->bi_status, sdp->sd_jdesc->jd_jid);
-		wake_up(&sdp->sd_logd_waitq);
-	}
+	if (bio->bi_status)
+		panic("Error %d writing to journal, jid=%u\n", bio->bi_status,
+		      sdp->sd_jdesc->jd_jid);
 
 	bio_for_each_segment_all(bvec, bio, i) {
 		page = bvec->bv_page;