linux-kernel - Re: [PATCH v2] fs-writeback: writeback_sb_inodes：Recalculate 'wrote' according skipped pages

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Date:   Tue, 19 Apr 2022 10:10:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Zhihao Cheng <chengzhihao1@...wei.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        yukuai3@...wei.com
Subject: Re: [PATCH v2] fs-writeback: writeback_sb_inodes：Recalculate 'wrote'
 according skipped pages

On Mon, Apr 18, 2022 at 12:43:43PM -0700, Linus Torvalds wrote:
> Similarly, tsk_is_pi_blocked() will disable the plug flush.

Bah, I'm forever confused by that clause... I did ask for a comment at
some point but that never seems to have happened.

  https://lore.kernel.org/all/20190816160626.12742-1-bigeasy@linutronix.de/T/#md983b64256814c046cec9ec875f4a975029b0daa

Seems to indicate it is about scheduling while holding a lock and the
unplug then leading to a deadlock.