From: Dmitry Vyukov <dvyukov@google.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nikolay Borisov <n.borisov.lkml@gmail.com>,
avagin <avagin@openvz.org>,
serge@hallyn.com, Kees Cook <keescook@chromium.org>,
Al Viro <viro@zeniv.linux.org.uk>,
LKML <linux-kernel@vger.kernel.org>,
syzkaller <syzkaller@googlegroups.com>
Subject: Re: namespace: deadlock in dec_pid_namespaces
Date: Mon, 23 Jan 2017 10:35:56 +0100 [thread overview]
Message-ID: <CACT4Y+ZoPu3iuo8Q_vORnJBn4m0PGMZjXTU1jWvGpt8Trs5tRw@mail.gmail.com> (raw)
In-Reply-To: <87lgu5w92e.fsf@xmission.com>
On Sat, Jan 21, 2017 at 1:28 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Nikolay Borisov <n.borisov.lkml@gmail.com> writes:
>
>> On 20.01.2017 20:05, Eric W. Biederman wrote:
>>> Nikolay Borisov <n.borisov.lkml@gmail.com> 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 <dvyukov@google.com>
prev parent reply other threads:[~2017-01-23 9:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-20 13:07 namespace: deadlock in dec_pid_namespaces Dmitry Vyukov
2017-01-20 13:26 ` Nikolay Borisov
2017-01-20 18:05 ` Eric W. Biederman
2017-01-20 22:44 ` Nikolay Borisov
2017-01-21 0:28 ` Eric W. Biederman
2017-01-23 9:35 ` Dmitry Vyukov [this message]
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