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Date:   Tue, 1 Aug 2023 01:47:31 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     "Darrick J. Wong" <djwong@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Dave Chinner <david@fromorbit.com>, Hao Xu <hao.xu@linux.dev>,
        io-uring@vger.kernel.org,
        Dominique Martinet <asmadeus@codewreck.org>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Stefan Roesch <shr@fb.com>, Clay Harris <bugs@claycon.org>,
        linux-fsdevel@vger.kernel.org, Wanpeng Li <wanpengli@tencent.com>
Subject: Re: [PATCH 3/5] io_uring: add support for getdents
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On Mon, Jul 31, 2023 at 06:28:02PM -0600, Jens Axboe wrote:
> It's also not an absolute thing, like memory allocations are. It's
> perfectly fine to grab a mutex under NOWAIT issue. What you should not
> do is grab a mutex that someone else can grab while waiting on IO. This
> kind of extra context is only available in the code in question, not
> generically for eg mutex locking.

Is that information documented somewhere?  I didn't know that was the
rule, and I wouldn't be surprised if that's news to several of the other
people on this thread.