Re: [block:for-3.14/core] kernel BUG at fs/bio.c:1748

[Chris Mason <clm@fb.com>]

On Tue, 2014-01-07 at 12:15 -0800, Muthu Kumar wrote:
> Thanks Fengguang. Final patch with added comment. BTW, fengguang
> mentioned that git-am has trouble with the inline patch and "quilt
> import" worked fine for him...
> 
> ------------
> In btrfs_end_bio(), we increment bi_remaining if is_orig_bio. If not,
> we restore the orig_bio but failed to increment bi_remaining for
> orig_bio, which triggers a BUG_ON later when bio_endio is called. Fix
> is to increment bi_remaining when we restore the orig bio as well.
> 

Hi everyone,

Which git tree is this against?  Just Jens or some extra code too?

I'll run some tests here.  My original patch is below (it's slightly
different from Muthu's).

Btrfs is sometimes calling bio_endio twice on the same bio while
we chain things.  This makes sure we don't trip over new assertions in
fs/bio.c

Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 7fcac70..5b30360 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -2289,6 +2289,10 @@ static void btrfsic_bio_end_io(struct bio *bp, int bio_error_status)
 		block = next_block;
 	} while (NULL != block);
 
+	/*
+	 * since we're not using bio_endio here, we don't need to worry about
+	 * the remaining count
+	 */
 	bp->bi_end_io(bp, bio_error_status);
 }
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 62176ad..786ddac 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1684,7 +1684,7 @@ static void end_workqueue_fn(struct btrfs_work *work)
 	bio->bi_private = end_io_wq->private;
 	bio->bi_end_io = end_io_wq->end_io;
 	kfree(end_io_wq);
-	bio_endio(bio, error);
+	bio_endio_nodec(bio, error);
 }
 
 static int cleaner_kthread(void *arg)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index ef48947..a31448f 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5284,9 +5284,17 @@ static void btrfs_end_bio(struct bio *bio, int err)
 		}
 	}
 
-	if (bio == bbio->orig_bio)
+	if (bio == bbio->orig_bio) {
 		is_orig_bio = 1;
 
+		/*
+		 * eventually we will call the bi_endio for the original bio,
+		 * make sure that we've properly bumped bi_remaining to reflect
+		 * our chain of endios here
+		 */
+		atomic_inc(&bio->bi_remaining);
+	}
+
 	if (atomic_dec_and_test(&bbio->stripes_pending)) {
 		if (!is_orig_bio) {
 			bio_put(bio);
--
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