linux-kernel - [PATCH 4.8 01/85] aoe: fix crash in page count manipulation

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Date:   Wed,  4 Jan 2017 21:46:46 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Tested-by: Don Koch" <kochd@...ibm.com>,
        Jens Axboe <axboe@...com>
Subject: [PATCH 4.8 01/85] aoe: fix crash in page count manipulation

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jens Axboe <axboe@...com>

commit 0cbc72a1781250f373327dd7e306e33859a42154 upstream.

aoeblk contains some mysterious code, that wants to elevate the bio
vec page counts while it's under IO. That is not needed, it's
fragile, and it's causing kernel oopses for some.

Reported-by: Tested-by: Don Koch <kochd@...ibm.com>
Tested-by: Tested-by: Don Koch <kochd@...ibm.com>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/aoe/aoecmd.c |   41 -----------------------------------------
 1 file changed, 41 deletions(-)

--- a/drivers/block/aoe/aoecmd.c
+++ b/drivers/block/aoe/aoecmd.c
@@ -853,45 +853,6 @@ rqbiocnt(struct request *r)
 	return n;
 }
 
-/* This can be removed if we are certain that no users of the block
- * layer will ever use zero-count pages in bios.  Otherwise we have to
- * protect against the put_page sometimes done by the network layer.
- *
- * See http://oss.sgi.com/archives/xfs/2007-01/msg00594.html for
- * discussion.
- *
- * We cannot use get_page in the workaround, because it insists on a
- * positive page count as a precondition.  So we use _refcount directly.
- */
-static void
-bio_pageinc(struct bio *bio)
-{
-	struct bio_vec bv;
-	struct page *page;
-	struct bvec_iter iter;
-
-	bio_for_each_segment(bv, bio, iter) {
-		/* Non-zero page count for non-head members of
-		 * compound pages is no longer allowed by the kernel.
-		 */
-		page = compound_head(bv.bv_page);
-		page_ref_inc(page);
-	}
-}
-
-static void
-bio_pagedec(struct bio *bio)
-{
-	struct page *page;
-	struct bio_vec bv;
-	struct bvec_iter iter;
-
-	bio_for_each_segment(bv, bio, iter) {
-		page = compound_head(bv.bv_page);
-		page_ref_dec(page);
-	}
-}
-
 static void
 bufinit(struct buf *buf, struct request *rq, struct bio *bio)
 {
@@ -899,7 +860,6 @@ bufinit(struct buf *buf, struct request
 	buf->rq = rq;
 	buf->bio = bio;
 	buf->iter = bio->bi_iter;
-	bio_pageinc(bio);
 }
 
 static struct buf *
@@ -1127,7 +1087,6 @@ aoe_end_buf(struct aoedev *d, struct buf
 	if (buf == d->ip.buf)
 		d->ip.buf = NULL;
 	rq = buf->rq;
-	bio_pagedec(buf->bio);
 	mempool_free(buf, d->bufpool);
 	n = (unsigned long) rq->special;
 	rq->special = (void *) --n;