From: "hch@lst.de" <hch@lst.de>
To: Bart Van Assche <Bart.VanAssche@wdc.com>
Cc: "hch@lst.de" <hch@lst.de>, "tj@kernel.org" <tj@kernel.org>,
"israelr@mellanox.com" <israelr@mellanox.com>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"maxg@mellanox.com" <maxg@mellanox.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"sagi@grimberg.me" <sagi@grimberg.me>
Subject: Re: [PATCH v4] blk-mq: Fix race conditions in request timeout handling
Date: Tue, 10 Apr 2018 16:50:16 +0200 [thread overview]
Message-ID: <20180410145016.GA25019@lst.de> (raw)
In-Reply-To: <f4bb15dff9dca995a9965204124caf2742798801.camel@wdc.com>
On Tue, Apr 10, 2018 at 01:26:39PM +0000, Bart Van Assche wrote:
> Can you explain why you think that using cmpxchg() is safe in this context?
> The regular completion path and the timeout code can both execute e.g. the
> following code concurrently:
>
> blk_mq_change_rq_state(rq, MQ_RQ_IN_FLIGHT, MQ_RQ_COMPLETE);
>
> That's why I think that we need an atomic compare and exchange instead of
> cmpxchg(). What I found in the Intel Software Developer Manual seems to
> confirm that:
The Linux cmpxchg() helper is supposed to always be atomic, you only
need atomic_cmpxchg and friends if you want to operate on an atomic_t.
(same for the _long variant).
In fact if you look at the x86 implementation of the cmpxchg() macro
you'll see that it will use the lock prefix if the kernel has been
built with CONFIG_SMP enabled.
next prev parent reply other threads:[~2018-04-10 14:50 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-10 1:34 [PATCH v4] blk-mq: Fix race conditions in request timeout handling Bart Van Assche
2018-04-10 7:59 ` jianchao.wang
2018-04-10 10:04 ` Ming Lei
2018-04-10 12:04 ` Shan Hai
2018-04-10 13:01 ` Bart Van Assche
2018-04-10 14:32 ` jianchao.wang
2018-04-10 8:41 ` Ming Lei
2018-04-10 12:58 ` Bart Van Assche
2018-04-10 13:55 ` Ming Lei
2018-04-10 14:09 ` Bart Van Assche
2018-04-10 14:30 ` Ming Lei
2018-04-10 15:02 ` Bart Van Assche
2018-04-10 15:25 ` Ming Lei
2018-04-10 15:30 ` tj
2018-04-10 15:38 ` Ming Lei
2018-04-10 15:40 ` tj
2018-04-10 21:33 ` tj
2018-04-10 21:46 ` Bart Van Assche
2018-04-10 21:54 ` tj
2018-04-11 12:50 ` Bart Van Assche
2018-04-11 14:16 ` tj
2018-04-11 18:38 ` Martin Steigerwald
2018-04-11 14:24 ` Sagi Grimberg
2018-04-11 14:43 ` tj
2018-04-11 16:16 ` Israel Rukshin
2018-04-11 17:07 ` tj
2018-04-11 21:31 ` tj
2018-04-12 8:59 ` Israel Rukshin
2018-04-12 13:35 ` tj
2018-04-15 12:28 ` Israel Rukshin
2018-04-18 16:34 ` Bart Van Assche
2018-04-10 9:55 ` Christoph Hellwig
2018-04-10 13:26 ` Bart Van Assche
2018-04-10 14:50 ` hch [this message]
2018-04-10 14:41 ` Jens Axboe
2018-04-10 14:20 ` Tejun Heo
2018-04-10 14:30 ` Bart Van Assche
2018-04-10 14:33 ` tj
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