linux-kernel - Re: namespace: deadlock in dec_pid

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Date:   Sat, 21 Jan 2017 00:44:24 +0200
From:   Nikolay Borisov <n.borisov.lkml@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, avagin <avagin@...nvz.org>,
        serge@...lyn.com, Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: namespace: deadlock in dec_pid_namespaces



On 20.01.2017 20:05, Eric W. Biederman wrote:
> Nikolay Borisov <n.borisov.lkml@...il.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? 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.

> 
> I a tired of being clever.
> 
> Eric
> 
> 

View attachment "0001-userns-Make-ucounts-lock-softirq-safe.patch" of type "text/x-patch" (2489 bytes)