From: Shakeel Butt <shakeelb@google.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: syzbot <syzbot+506c8a2a115201881d45@syzkaller.appspotmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Eric Dumazet <edumazet@google.com>,
Mina Almasry <almasrymina@google.com>,
Michal Hocko <mhocko@suse.com>
Subject: Re: possible deadlock in sk_clone_lock
Date: Fri, 26 Feb 2021 16:00:30 -0800 [thread overview]
Message-ID: <CALvZod5qODDSxqHqQ=_1roYVGVVvEvP3FnYMnAPQZgvUjxotsw@mail.gmail.com> (raw)
In-Reply-To: <7b7c4f41-b72e-840f-278a-320b9d97f887@oracle.com>
On Fri, Feb 26, 2021 at 3:14 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> Cc: Michal
>
> On 2/26/21 2:44 PM, Shakeel Butt wrote:
> > On Fri, Feb 26, 2021 at 2:09 PM syzbot
> > <syzbot+506c8a2a115201881d45@syzkaller.appspotmail.com> wrote:
> <snip>
> >> other info that might help us debug this:
> >>
> >> Possible interrupt unsafe locking scenario:
> >>
> >> CPU0 CPU1
> >> ---- ----
> >> lock(hugetlb_lock);
> >> local_irq_disable();
> >> lock(slock-AF_INET);
> >> lock(hugetlb_lock);
> >> <Interrupt>
> >> lock(slock-AF_INET);
> >>
> >> *** DEADLOCK ***
> >
> > This has been reproduced on 4.19 stable kernel as well [1] and there
> > is a reproducer as well.
> >
> > It seems like sendmsg(MSG_ZEROCOPY) from a buffer backed by hugetlb. I
> > wonder if we just need to make hugetlb_lock softirq-safe.
> >
> > [1] https://syzkaller.appspot.com/bug?extid=6383ce4b0b8ec575ad93
>
> Thanks Shakeel,
>
> Commit c77c0a8ac4c5 ("mm/hugetlb: defer freeing of huge pages if in non-task
> context") attempted to address this issue. It uses a work queue to
> acquire hugetlb_lock if the caller is !in_task().
>
> In another recent thread, there was the suggestion to change the
> !in_task to in_atomic.
>
> I need to do some research on the subtle differences between in_task,
> in_atomic, etc. TBH, I 'thought' !in_task would prevent the issue
> reported here. But, that obviously is not the case.
I think the freeing is happening in the process context in this report
but it is creating the lock chain from softirq-safe slock to
irq-unsafe hugetlb_lock. So, two solutions I can think of are: (1)
always defer the freeing of hugetlb pages to a work queue or (2) make
hugetlb_lock softirq-safe.
next prev parent reply other threads:[~2021-02-27 0:01 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-26 21:08 possible deadlock in sk_clone_lock syzbot
2021-02-26 22:44 ` Shakeel Butt
2021-02-26 23:14 ` Mike Kravetz
2021-02-27 0:00 ` Shakeel Butt [this message]
2021-03-01 12:11 ` Michal Hocko
2021-03-01 15:10 ` Shakeel Butt
2021-03-01 15:57 ` Michal Hocko
2021-03-01 16:39 ` Shakeel Butt
2021-03-01 17:23 ` Michal Hocko
2021-03-02 1:16 ` Mike Kravetz
2021-03-02 9:44 ` Michal Hocko
[not found] ` <CALvZod7XHbjfoGGVH=h17u8-FruMaiPMWxXJz5JBmeJkNHBqNQ@mail.gmail.com>
[not found] ` <YD5L1K3EWVWh1ULr@dhcp22.suse.cz>
[not found] ` <06edda9a-dce9-accd-11a3-97f6d5243ed1@oracle.com>
2021-03-03 3:59 ` Shakeel Butt
2021-03-05 9:09 ` Michal Hocko
2021-03-03 8:03 ` Michal Hocko
2021-03-03 17:59 ` Paul E. McKenney
2021-03-04 9:58 ` Michal Hocko
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