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[PATCH v4 0/7] blk-mq: fix race conditions on cpu hotplug handling

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  [PATCH v4 0/7] blk-mq: fix race conditions on cpu hotplug handling Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:10 +0200
    [PATCH v4 4/7] blk-mq: fix q->mq_usage_counter access race Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
    [PATCH v4 5/7] blk-mq: avoid inserting requests before establishing new mapping Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
      Re: [PATCH v4 5/7] blk-mq: avoid inserting requests before  establishing new mapping Christoph Hellwig <hch@lst.de> - 2015-09-29 09:00 +0200
    [PATCH v4 2/7] blk-mq: fix sysfs registration/unregistration race Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
    [PATCH v4 1/7] blk-mq: avoid setting hctx->tags->cpumask before allocation Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
      Re: [PATCH v4 1/7] blk-mq: avoid setting hctx->tags->cpumask  before allocation Christoph Hellwig <hch@lst.de> - 2015-09-26 20:20 +0200
    [PATCH v4 7/7] blk-mq: fix deadlock when reading cpu_list Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
    [PATCH v4 6/7] blk-mq: fix freeze queue race Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
      Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Tejun Heo <tj@kernel.org> - 2015-09-26 19:40 +0200
        Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-27 15:10 +0200
          Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Tejun Heo <tj@kernel.org> - 2015-09-28 16:50 +0200
            Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Christoph Hellwig <hch@lst.de> - 2015-09-29 09:00 +0200
            Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Tejun Heo <tj@kernel.org> - 2015-09-29 17:10 +0200
              Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Tejun Heo <tj@kernel.org> - 2015-09-30 00:00 +0200
                Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-30 12:40 +0200
            Re: [PATCH v4 6/7] blk-mq: fix freeze queue race Jens Axboe <axboe@kernel.dk> - 2015-09-29 17:10 +0200
    [PATCH v4 3/7] blk-mq: Fix use after of free q->mq_map Akinobu Mita <akinobu.mita@gmail.com> - 2015-09-26 19:20 +0200
      Re: [PATCH v4 3/7] blk-mq: Fix use after of free q->mq_map Christoph Hellwig <hch@lst.de> - 2015-09-29 09:00 +0200
        Re: [PATCH v4 3/7] blk-mq: Fix use after of free q->mq_map Akinobu Mita <akinobu.mita@gmail.com> - 2015-10-06 02:00 +0200
          Re: [PATCH v4 3/7] blk-mq: Fix use after of free q->mq_map Christoph Hellwig <hch@lst.de> - 2015-10-06 11:50 +0200
    Re: [PATCH v4 0/7] blk-mq: fix race conditions on cpu hotplug  handling Jens Axboe <axboe@kernel.dk> - 2015-09-29 19:40 +0200

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#1240326 — Re: [PATCH v4 3/7] blk-mq: Fix use after of free q->mq_map

On Tue, Oct 06, 2015 at 08:50:47AM +0900, Akinobu Mita wrote:
> 2015-09-29 15:52 GMT+09:00 Christoph Hellwig <hch@lst.de>:
> > Looks good,
> >
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> >
> > Can you also add a patch that renames blk_mq_free_queue to
> > blk_mq_cleaup_queue and adds a comment that we should not free any memory
> > here?  We had  way too many bugs of this kinds unfortunately.
> 
> Renaming blk_mq_free_queue to blk_mq_cleaup_queue sounds good because
> it is called from blk_cleanup_queue().
> 
> How about adding comment like below?

This looks great.  It's a lot more than what I though but it looks correct
and useful!
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#1235428 — Re: [PATCH v4 0/7] blk-mq: fix race conditions on cpu hotplug handling

On 09/26/2015 11:09 AM, Akinobu Mita wrote:
> This patchset addresses several race conditions on cpu hotplug handling
> for blk-mq.  All problems can be reproducible by the following script.
>
> while true; do
> 	echo 0 > /sys/devices/system/cpu/cpu1/online
> 	echo 1 > /sys/devices/system/cpu/cpu1/online
> done &
>
> while true; do
> 	modprobe -r null_blk
> 	modprobe null_blk queue_mode=2 irqmode=1
> 	sleep 0.1
> done
>
> * Changes from v3
> - Rebased to the latest kernel
> - Add Reviewed-by tags

I've reviewed the patches, looks good to me. I've skipped 6/7, as I 
think we should fix that as part of the percpu ref counting, and not 
handle it specifically in blk-mq. If we can't get that fix before 4.3 
wraps up, then we can revisit and put that in as well.

Thanks!

-- 
Jens Axboe

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