linux-kernel - Re: [PATCH] sched: fix tsk->pi_lock isn't held when do_set_cpus

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <BLU436-SMTP236A549D58B8A4A1A4E7F9680610@phx.gbl>
Date:	Tue, 25 Aug 2015 18:18:36 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: fix tsk->pi_lock isn't held when
 do_set_cpus_allowed()

On 8/25/15 6:05 PM, Peter Zijlstra wrote:
> On Tue, Aug 25, 2015 at 03:59:54PM +0800, Wanpeng Li wrote:
>> +++ b/kernel/cpuset.c
>> @@ -2376,8 +2376,12 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
>>   
>>   void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
>>   {
>> +	unsigned long flags;
>> +
>>   	rcu_read_lock();
>> +	raw_spin_lock_irqsave(&tsk->pi_lock, flags);
>>   	do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus);
>> +	raw_spin_lock_irqsave(&tsk->pi_lock, flags);
>>   	rcu_read_unlock();
> Aside from the double lock thing that was already pointed out, I think
> this is wrong, because the select_task_rq() call can already have
> pi_lock held.
>
> Taking it again would result in a deadlock.
>
> Consider for instance:
>
> try_to_wake_up()
>    raw_spin_lock_irqsave(->pi_lock)
>    select_task_rq()
>      select_ballback_rq()
>        cpuset_cpus_allowed_fallback()
>          raw_spin_lock_irqsave(->pi_lock)
>
>
> The problem is with the migration path and should be fixed there.

Indeed, it should be fixed in migration path. I will try to fight it out 
and post a patch. :)

Regards,
Wanpeng Li

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/