Avoid recursion on bio_endio. bio_endio calls bio->bi_end_io which may in turn
call bio_endio again. When this recursion happens, put the new bio to the queue
and process it later, from the top-level bio_endio.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 fs/bio.c            |   39 ++++++++++++++++++++++++++++++++++++---
 include/linux/bio.h |    3 +++
 2 files changed, 39 insertions(+), 3 deletions(-)

Index: linux-2.6.31-rc3-devel/fs/bio.c
===================================================================
--- linux-2.6.31-rc3-devel.orig/fs/bio.c	2009-07-14 16:07:22.000000000 +0200
+++ linux-2.6.31-rc3-devel/fs/bio.c	2009-07-14 16:07:52.000000000 +0200
@@ -1390,15 +1390,48 @@ void bio_check_pages_dirty(struct bio *b
  *   bio unless they own it and thus know that it has an end_io
  *   function.
  **/
+static DEFINE_PER_CPU(struct bio **, bio_end_queue) = { NULL };
+
 void bio_endio(struct bio *bio, int error)
 {
+	struct bio ***bio_end_queue_ptr;
+	struct bio *bio_queue;
+
+	unsigned long flags;
+
+	bio->bi_flags &= ~(1 << BIO_SEG_VALID);
+	bio->bi_phys_segments = error;
 	if (error)
 		clear_bit(BIO_UPTODATE, &bio->bi_flags);
 	else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
-		error = -EIO;
+		bio->bi_phys_segments = -EIO;
+
+	local_irq_save(flags);
+	bio_end_queue_ptr = &__get_cpu_var(bio_end_queue);
+
+	if (*bio_end_queue_ptr) {
+		**bio_end_queue_ptr = bio;
+		*bio_end_queue_ptr = &bio->bi_next;
+		bio->bi_next = NULL;
+	} else {
+		bio_queue = NULL;
+		*bio_end_queue_ptr = &bio_queue;
+
+next_bio:
+		if (bio->bi_end_io)
+			bio->bi_end_io(bio, (short)bio->bi_phys_segments);
+
+		if (bio_queue) {
+			bio = bio_queue;
+			bio_queue = bio->bi_next;
+			if (!bio_queue)
+				*bio_end_queue_ptr = &bio_queue;
+			goto next_bio;
+		}
+		*bio_end_queue_ptr = NULL;
+	}
 
-	if (bio->bi_end_io)
-		bio->bi_end_io(bio, error);
+	local_irq_restore(flags);
 }
 
 void bio_pair_release(struct bio_pair *bp)
Index: linux-2.6.31-rc3-devel/include/linux/bio.h
===================================================================
--- linux-2.6.31-rc3-devel.orig/include/linux/bio.h	2009-07-14 16:06:25.000000000 +0200
+++ linux-2.6.31-rc3-devel/include/linux/bio.h	2009-07-14 16:07:52.000000000 +0200
@@ -74,6 +74,9 @@ struct bio {
 
 	/* Number of segments in this BIO after
 	 * physical address coalescing is performed.
+	 *
+	 * When ending a bio request in bio_endio, this field is temporarily
+	 * (ab)used to keep the error code.
 	 */
 	unsigned int		bi_phys_segments;