From: ebiederm@xmission.com (Eric W. Biederman)
To: Nikolay Borisov <n.borisov.lkml@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.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: Sat, 21 Jan 2017 13:28:09 +1300 [thread overview]
Message-ID: <87lgu5w92e.fsf@xmission.com> (raw)
In-Reply-To: <fba89f51-5db7-a6e2-2715-eee120146b9e@gmail.com> (Nikolay Borisov's message of "Sat, 21 Jan 2017 00:44:24 +0200")
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.
Eric
next prev parent reply other threads:[~2017-01-21 0:33 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 [this message]
2017-01-23 9:35 ` Dmitry Vyukov
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