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Date:   Mon, 23 Jan 2017 10:35:56 +0100
From:   Dmitry Vyukov <>
To:     "Eric W. Biederman" <>
Cc:     Nikolay Borisov <>,
        avagin <>,,
        Kees Cook <>,
        Al Viro <>,
        LKML <>,
        syzkaller <>
Subject: Re: namespace: deadlock in dec_pid_namespaces

On Sat, Jan 21, 2017 at 1:28 AM, Eric W. Biederman
<> wrote:
> Nikolay Borisov <> writes:
>> On 20.01.2017 20:05, Eric W. Biederman wrote:
>>> Nikolay Borisov <> writes:
>>>> On 20.01.2017 15:07, Dmitry Vyukov wrote:
>>>>> Hello,
>>>>> I've got the following deadlock report while running syzkaller fuzzer
>>>>> on eec0d3d065bfcdf9cd5f56dd2a36b94d12d32297 of linux-next (on odroid
>>>>> device if it matters):
>>> I am puzzled I thought we had fixed this with:
>>>   add7c65ca426 ("pid: fix lockdep deadlock warning due to ucount_lock")
>>> But apparently not.  We  just moved it from hardirq to softirq context.  Bah.
>>> Thank you very much for the report.
>>> Nikolay can you make your change use spinlock_irq?  And have put_ucounts
>>> do spin_lock_irqsave?  That way we just don't care where we call this.
>> Like the one attached?
> Exactly thank you.  Dmitry if you have time to test that patch and
> verify it fixes your issue I would appreciate it.
>> I haven't really taken careful look as to whether
>> the function where _irq versions do fiddle with irq state, since this
>> might cause a problem if we unconditionally enable them.
> In code paths where we can sleep irqs must come in enabled or it's a
> bug.
> spin_lock_irq which unconditionally disables irqs is thus safe on the
> allocation path.
> Similary spin_unlock_irq which unconditionally enables irqs is also safe
> on the allocation path.

Yes, it fixes the issue for me:

Tested-by: Dmitry Vyukov <>

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