[3.19.y-ckt stable] Patch "block: Always check queue limits for cloned requests" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    block: Always check queue limits for cloned requests

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt12.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 0175ce6b59d2753c4c9cd8a075b9c337eba8ce0b Mon Sep 17 00:00:00 2001
From: Hannes Reinecke <hare at suse.de>
Date: Thu, 26 Nov 2015 08:46:57 +0100
Subject: block: Always check queue limits for cloned requests

commit bf4e6b4e757488dee1b6a581f49c7ac34cd217f8 upstream.

When a cloned request is retried on other queues it always needs
to be checked against the queue limits of that queue.
Otherwise the calculations for nr_phys_segments might be wrong,
leading to a crash in scsi_init_sgtable().

To clarify this the patch renames blk_rq_check_limits()
to blk_cloned_rq_check_limits() and removes the symbol
export, as the new function should only be used for
cloned requests and never exported.

Cc: Mike Snitzer <snitzer at redhat.com>
Cc: Ewan Milne <emilne at redhat.com>
Cc: Jeff Moyer <jmoyer at redhat.com>
Signed-off-by: Hannes Reinecke <hare at suse.de>
Fixes: e2a60da74 ("block: Clean up special command handling logic")
Acked-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Jens Axboe <axboe at fb.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 block/blk-core.c       | 21 +++++++--------------
 include/linux/blkdev.h |  1 -
 2 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 3ad4055..adb49b4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1985,7 +1985,8 @@ void submit_bio(int rw, struct bio *bio)
 EXPORT_SYMBOL(submit_bio);

 /**
- * blk_rq_check_limits - Helper function to check a request for the queue limit
+ * blk_cloned_rq_check_limits - Helper function to check a cloned request
+ *                              for new the queue limits
  * @q:  the queue
  * @rq: the request being checked
  *
@@ -1996,20 +1997,13 @@ EXPORT_SYMBOL(submit_bio);
  *    after it is inserted to @q, it should be checked against @q before
  *    the insertion using this generic function.
  *
- *    This function should also be useful for request stacking drivers
- *    in some cases below, so export this function.
  *    Request stacking drivers like request-based dm may change the queue
- *    limits while requests are in the queue (e.g. dm's table swapping).
- *    Such request stacking drivers should check those requests against
- *    the new queue limits again when they dispatch those requests,
- *    although such checkings are also done against the old queue limits
- *    when submitting requests.
+ *    limits when retrying requests on other queues. Those requests need
+ *    to be checked against the new queue limits again during dispatch.
  */
-int blk_rq_check_limits(struct request_queue *q, struct request *rq)
+static int blk_cloned_rq_check_limits(struct request_queue *q,
+				      struct request *rq)
 {
-	if (!rq_mergeable(rq))
-		return 0;
-
 	if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, rq->cmd_flags)) {
 		printk(KERN_ERR "%s: over max size limit.\n", __func__);
 		return -EIO;
@@ -2029,7 +2023,6 @@ int blk_rq_check_limits(struct request_queue *q, struct request *rq)

 	return 0;
 }
-EXPORT_SYMBOL_GPL(blk_rq_check_limits);

 /**
  * blk_insert_cloned_request - Helper for stacking drivers to submit a request
@@ -2041,7 +2034,7 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
 	unsigned long flags;
 	int where = ELEVATOR_INSERT_BACK;

-	if (blk_rq_check_limits(q, rq))
+	if (blk_cloned_rq_check_limits(q, rq))
 		return -EIO;

 	if (rq->rq_disk &&
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 92f4b4b..25ac915 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -797,7 +797,6 @@ extern void blk_rq_set_block_pc(struct request *);
 extern void blk_requeue_request(struct request_queue *, struct request *);
 extern void blk_add_request_payload(struct request *rq, struct page *page,
 		unsigned int len);
-extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
 extern int blk_lld_busy(struct request_queue *q);
 extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
 			     struct bio_set *bs, gfp_t gfp_mask,
--
1.9.1