This is a note to let you know that I've just added the patch titled
block: blk-flush shouldn't call directly into q->request_fn()
__blk_run_queue()
to the 2.6.37-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
block-blk-flush-shouldn-t-call-directly-into-q-request_fn-__blk_run_queue.patch
and it can be found in the queue-2.6.37 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 255bb490c8c27eed484d538efe6ef6a7473bd3f6 Mon Sep 17 00:00:00 2001
From: Tejun Heo <[email protected]>
Date: Wed, 2 Mar 2011 08:48:06 -0500
Subject: block: blk-flush shouldn't call directly into q->request_fn()
__blk_run_queue()
From: Tejun Heo <[email protected]>
commit 255bb490c8c27eed484d538efe6ef6a7473bd3f6 upstream.
blk-flush decomposes a flush into sequence of multiple requests. On
completion of a request, the next one is queued; however, block layer
must not implicitly call into q->request_fn() directly from completion
path. This makes the queue behave unexpectedly when seen from the
drivers and violates the assumption that q->request_fn() is called
with process context + queue_lock.
This patch makes blk-flush the following two changes to make sure
q->request_fn() is not called directly from request completion path.
- blk_flush_complete_seq_end_io() now asks __blk_run_queue() to always
use kblockd instead of calling directly into q->request_fn().
- queue_next_fseq() uses ELEVATOR_INSERT_REQUEUE instead of
ELEVATOR_INSERT_FRONT so that elv_insert() doesn't try to unplug the
request queue directly.
Reported by Jan in the following threads.
http://thread.gmane.org/gmane.linux.ide/48778
http://thread.gmane.org/gmane.linux.ide/48786
stable: applicable to v2.6.37.
Signed-off-by: Tejun Heo <[email protected]>
Reported-by: Jan Beulich <[email protected]>
Cc: "David S. Miller" <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
block/blk-flush.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -66,10 +66,12 @@ static void blk_flush_complete_seq_end_i
/*
* Moving a request silently to empty queue_head may stall the
- * queue. Kick the queue in those cases.
+ * queue. Kick the queue in those cases. This function is called
+ * from request completion path and calling directly into
+ * request_fn may confuse the driver. Always use kblockd.
*/
if (was_empty && next_rq)
- __blk_run_queue(q, false);
+ __blk_run_queue(q, true);
}
static void pre_flush_end_io(struct request *rq, int error)
@@ -130,7 +132,7 @@ static struct request *queue_next_fseq(s
BUG();
}
- elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+ elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
return rq;
}
Patches currently in stable-queue which might be from [email protected] are
queue-2.6.37/block-blk-flush-shouldn-t-call-directly-into-q-request_fn-__blk_run_queue.patch
queue-2.6.37/blk-throttle-do-not-use-kblockd-workqueue-for-throtl-work.patch
queue-2.6.37/block-add-force_kblockd-to-__blk_run_queue.patch
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