linux-kernel - Re: [PATCH] swap_readpage: avoid blk_wake_io

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Message-ID: <alpine.LSU.2.11.1907041408040.1762@eggly.anvils>
Date:   Thu, 4 Jul 2019 14:15:33 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Oleg Nesterov <oleg@...hat.com>, Qian Cai <cai@....pw>,
        axboe@...nel.dk, hch@....de, peterz@...radead.org,
        gkohli@...eaurora.org, mingo@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] swap_readpage: avoid blk_wake_io_task() if
 !synchronous

On Thu, 4 Jul 2019, Andrew Morton wrote:
> On Thu, 4 Jul 2019 18:03:01 +0200 Oleg Nesterov <oleg@...hat.com> wrote:
> 
> > swap_readpage() sets waiter = bio->bi_private even if synchronous = F,
> > this means that the caller can get the spurious wakeup after return. This
> > can be fatal if blk_wake_io_task() does set_current_state(TASK_RUNNING)
> > after the caller does set_special_state(), in the worst case the kernel
> > can crash in do_task_dead().
> 
> I think we need a Fixes: and a cc:stable here?
> 
> IIRC, we're fixing 0619317ff8baa2 ("block: add polled wakeup task helper").

Yes, you are right.

But catch me by surprise: I had been thinking this was a 5.2 regression.
I guess something in 5.2 (doesn't matter what) has made it significantly
easier to hit: but now I look at old records, see that I hit it once on
5.0-rc1, then never again until 5.2.

Thanks, and to Oleg,
Hugh