linux-kernel - Re: [PATCH] debugobject: don't wake up kswapd from fill

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Message-ID: <39c79d27-73ea-06a8-62fe-2b64d0fd8db5@I-love.SAKURA.ne.jp>
Date:   Fri, 12 May 2023 22:09:33 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     syzbot <syzbot+fe0c72f0ccbb93786380@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com, Ingo Molnar <mingo@...e.hu>,
        linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] debugobject: don't wake up kswapd from fill_pool()

On 2023/05/12 21:54, Thomas Gleixner wrote:
> On Fri, May 12 2023 at 19:57, Tetsuo Handa wrote:
>> On 2023/05/12 12:44, Andrew Morton wrote:
>>> On Thu, 11 May 2023 22:47:32 +0900 Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:
>>>
>>>> syzbot is reporting lockdep warning in fill_pool(), for GFP_ATOMIC is
>>>> (__GFP_HIGH | __GFP_KSWAPD_RECLAIM) which wakes up kswapd.
>>>> Since fill_pool() might be called with arbitrary locks held,
>>>> fill_pool() should not assume that holding pgdat->kswapd_wait is safe.
> 
> https://lore.kernel.org/lkml/871qjldbes.ffs@tglx/

.config says IS_ENABLED(CONFIG_PREEMPT_RT) == false, and lockdep says about
base->lock => pgdat->kswapd_wait => p->pi_lock => rq->__lock => base->lock
dependency but does not say about db->lock.

How can your patch fix this problem?