From: Shaohua Li <shli@kernel.org>
Date: Tue, 31 Dec 2013 03:38:50 +0000 (+0800)
Subject: blk-mq: Don't reserve a tag for flush request
X-Git-Tag: v3.14-rc3~22^2~23
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f0276924fa35a3607920a58cf5d878212824b951;p=pandora-kernel.git

blk-mq: Don't reserve a tag for flush request

Reserving a tag (request) for flush to avoid dead lock is a overkill. A
tag is valuable resource. We can track the number of flush requests and
disallow having too many pending flush requests allocated. With this
patch, blk_mq_alloc_request_pinned() could do a busy nop (but not a dead
loop) if too many pending requests are allocated and new flush request
is allocated. But this should not be a problem, too many pending flush
requests are very rare case.

I verified this can fix the deadlock caused by too many pending flush
requests.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

Reading git-diff-tree failed