linux-ext4 - Re: possible deadlock in start_this

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Date:   Fri, 12 Feb 2021 12:22:07 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Michal Hocko <mhocko@...e.com>, Jan Kara <jack@...e.cz>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+bfdded10ab7dcd7507ae@...kaller.appspotmail.com>,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Theodore Ts'o <tytso@....edu>, Linux-MM <linux-mm@...ck.org>
Subject: Re: possible deadlock in start_this_handle (2)

On Fri, Feb 12, 2021 at 08:18:11PM +0900, Tetsuo Handa wrote:
> On 2021/02/12 1:41, Michal Hocko wrote:
> > But I suspect we have drifted away from the original issue. I thought
> > that a simple check would help us narrow down this particular case and
> > somebody messing up from the IRQ context didn't sound like a completely
> > off.
> > 
> 
>  From my experience at https://lkml.kernel.org/r/201409192053.IHJ35462.JLOMOSOFFVtQFH@I-love.SAKURA.ne.jp ,
> I think we can replace direct PF_* manipulation with macros which do not receive "struct task_struct *" argument.
> Since TASK_PFA_TEST()/TASK_PFA_SET()/TASK_PFA_CLEAR() are for manipulating PFA_* flags on a remote thread, we can
> define similar ones for manipulating PF_* flags on current thread. Then, auditing dangerous users becomes easier.

No, nobody is manipulating another task's GFP flags.