linux-kernel - [PATCH v1 0/2] blk-mq: fix oops caused by CPU hotplug

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Date:	Tue, 21 Apr 2015 10:00:18 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org
Cc:	Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
	Maxim Patlasov <mpatlasov@...allels.com>
Subject: [PATCH v1 0/2] blk-mq: fix oops caused by CPU hotplug

Hi Guys,

Dongsu Park reported[1] that kernel oops can be triggered easily by
CPU plug when there is pending I/O on virtio-scsi.

Turns out two problems exist in blk-mq core code and both can trigger
oops by CPU plug:
        - timeout handling vs CPU hotplug, especially unmapped hw queue tags
        is still touched by timeout handler
        - in case of shared tags, there is one bug about setting and checking
        hctx->tags during CPU hotplug

The two patches fix the two problem, and Dongsu has verified that
the oops is fixed with the two patches too.

[1], http://marc.info/?t=142926389200008&r=1&w=2

V1:
	- update comment
	- moving tags allocation in blk_mq_map_swqueue() because
	unmapped hw queue can be remapped after CPU topo is changed

 block/blk-mq.c |   50 ++++++++++++++++++++++++++------------------------
 1 file changed, 26 insertions(+), 24 deletions(-)


Thanks,
Ming Lei

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