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From: Matthew Wilcox <willy@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Vishal Moola <vishal.moola@gmail.com>,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] Page Cache Allowing Hard Interrupts
Date: Tue, 10 Aug 2021 13:09:45 +0100	[thread overview]
Message-ID: <YRJsiapS/M3BOH9D@casper.infradead.org> (raw)
In-Reply-To: <YRI1oLdiueUbBVwb@infradead.org>

On Tue, Aug 10, 2021 at 09:15:28AM +0100, Christoph Hellwig wrote:
> Stupid question, but where do we ever do page cache interaction from
> soft irq context?

test_clear_page_writeback() happens in _some_ interrupt context (ie
the io completion path).  We had been under the impression that it was
always actually softirq context, and so this patch was safe.  However,
it's now clear that some drivers are calling it from hardirq context.
Writeback completions are clearly not latency sensitive and so can
be delayed from hardirq to softirq context without any problem, so I
think fixing this is just going to be a matter of tagging requests as
"complete in softirq context" and ensuring that blk_mq_raise_softirq()
is called for them.

Assuming that DIO write completions _are_ latency-sensitive, of course.
Maybe all write completions could be run in softirqs.

  reply	other threads:[~2021-08-10 12:10 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 21:36 Vishal Moola
2021-07-31 14:31 ` dc1468867f: WARNING:at_mm/workingset.c:#workingset_update_node kernel test robot
2021-08-10  8:15 ` [RFC PATCH] Page Cache Allowing Hard Interrupts Christoph Hellwig
2021-08-10 12:09   ` Matthew Wilcox [this message]
2021-08-10 12:33     ` Christoph Hellwig
2021-08-10 14:08       ` Matthew Wilcox

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