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Date:   Mon, 19 Jul 2021 11:16:10 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Hou Tao <houtao1@huawei.com>, Jens Axboe <axboe@kernel.dk>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        yukuai3@huawei.com, will@kernel.org, peterz@infradead.org
Subject: Re: [PATCH] block: ensure the memory order between bi_private and
 bi_status
Message-ID: <20210719181610.GA4397@paulmck-ThinkPad-P17-Gen-1>
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References: <20210701113537.582120-1-houtao1@huawei.com>
 <20210715070148.GA8088@lst.de>
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On Thu, Jul 15, 2021 at 09:01:48AM +0200, Christoph Hellwig wrote:
> On Thu, Jul 01, 2021 at 07:35:37PM +0800, Hou Tao wrote:

[ . . . ]

> > Fixing it by using smp_load_acquire() & smp_store_release() to guarantee
> > the order between {bio->bi_private|dio->waiter} and {bi_status|bi_blkg}.
> > 
> > Fixes: 189ce2b9dcc3 ("block: fast-path for small and simple direct I/O requests")
> 
> This obviously does not look broken, but smp_load_acquire /
> smp_store_release is way beyond my paygrade.  Adding some CCs.

Huh.

I think that it was back in 2006 when I first told Linus that my goal was
to make memory ordering routine.  I clearly have not yet achieved that
goal, even given a lot of help from a lot of people over a lot of years.

Oh well, what is life without an ongoing challenge?  ;-)

							Thanx, Paul