linux-kernel - Re: [PATCH v4] CPU hotplug: active_writer not woken up in some cases

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 for Android: free password hash cracker in your pocket

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

Date:	Fri, 12 Dec 2014 09:46:36 +0100
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, heiko.carstens@...ibm.com,
	borntraeger@...ibm.com, rafael.j.wysocki@...el.com,
	paulmck@...ux.vnet.ibm.com, peterz@...radead.org, bp@...e.de,
	jkosina@...e.cz
Subject: Re: [PATCH v4] CPU hotplug: active_writer not woken up in some
 cases - deadlock


> This is subjective, but how about
> 
> 	static bool xxx(void)
> 	{
> 		mutex_lock(&cpu_hotplug.lock);
> 		if (atomic_read(&cpu_hotplug.refcount) == 0)
> 			return true;
> 		mutex_unlock(&cpu_hotplug.lock);
> 		return false;
> 	}
> 
> 	void cpu_hotplug_begin(void)
> 	{
> 		cpu_hotplug.active_writer = current;
> 
> 		cpuhp_lock_acquire();
> 		wait_event(&cpu_hotplug.wq, xxx());
> 	}
> 
> instead?
> 
> Oleg.
> 

[   50.662459] do not call blocking ops when !TASK_RUNNING; state=2 set at [<000000000017340e>] prepare_to_wait_event+0x7a/0x124
[   50.662472] ------------[ cut here ]------------
[   50.662475] WARNING: at kernel/sched/core.c:7301
[   50.662477] Modules linked in:
[   50.662482] CPU: 5 PID: 225 Comm: cpu_start_stop. Not tainted 3.18.0+ #59
[   50.662485] task: 0000000001f94b20 ti: 0000000001ffc000 task.ti: 0000000001ffc000
...

Looks like your suggestion won't work. We can only set the task to
TASK_UNINTERRUPTIBLE after taking the lock.

David

--
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/