linux-kernel - Re: [PATCH] sbitmap: Protect swap

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Message-ID: <CAHk-=wh6GsuJSoRH_2KzRVAggzeJTVo8W4uBWMi+7GATf3YzYg@mail.gmail.com>
Date:   Tue, 15 Jan 2019 07:32:59 +1200
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Jens Axboe <axboe@...nel.dk>, LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Clark Williams <williams@...hat.com>,
        Bart Van Assche <bvanassche@....org>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH] sbitmap: Protect swap_lock from softirqs

On Tue, Jan 15, 2019 at 5:25 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> The swap_lock used by sbitmap has a chain with locks taken from
> softirq, but the swap_lock is not protected from being preempted by
> softirqs.
>
> A chain exists of:
>
>  sbq->ws[i].wait -> dispatch_wait_lock -> swap_lock
>
> Where the sbq->ws[i].wait lock can be taken from softirq context, which
> means all locks below it in the chain must also be protected from
> softirqs.
>
> Cc: stable@...r.kernel.org

Ack and applied, except for the "stable" tag.

Both the original buggy code, and the incorrect "shut up lockdep" were
only merged after 4.20.

                 Linus