From: Omar Sandoval <osandov@osandov.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Omar Sandoval <osandov@fb.com>,
Yi Zhang <yi.zhang@redhat.com>,
"jianchao.wang" <jianchao.w.wang@oracle.com>
Subject: Re: [PATCH V3] sbitmap: order READ/WRITE freed instance and setting clear bit
Date: Mon, 25 Mar 2019 11:52:17 -0700 [thread overview]
Message-ID: <20190325185217.GE5826@vader> (raw)
In-Reply-To: <20190322011351.4082-1-ming.lei@redhat.com>
On Fri, Mar 22, 2019 at 09:13:51AM +0800, Ming Lei wrote:
> Inside sbitmap_queue_clear(), once the clear bit is set, it will be
> visiable to allocation path immediately. Meantime READ/WRITE on old
> associated instance(such as request in case of blk-mq) may be
> out-of-order with the setting clear bit, so race with re-allocation
> may be triggered.
>
> Adds one memory barrier for ordering READ/WRITE of the freed associated
> instance with setting clear bit for avoiding race with re-allocation.
Just to make sure I understand, the race is something like this?
Thread 1 Thread 2
sbitmap_queue_get()
...
write to request _____
sbitmap_queue_clear() \
\ sbitmap_queue_get()
\______ observes write
If so, you can add
Reviewed-by: Omar Sandoval <osandov@fb.com>
next prev parent reply other threads:[~2019-03-25 18:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-22 1:13 [PATCH V3] sbitmap: order READ/WRITE freed instance and setting clear bit Ming Lei
2019-03-25 18:52 ` Omar Sandoval [this message]
2019-03-26 1:33 ` Ming Lei
2019-03-26 3:10 ` Jens Axboe
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