linux-kernel - Re: [BUG] WARNING: at kernel/trace/ring

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: <4B95C1FC.9030307@cn.fujitsu.com>
Date:	Tue, 09 Mar 2010 11:35:24 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	rostedt@...dmis.org
CC:	Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

Steven Rostedt wrote:
> On Mon, 2010-03-08 at 10:03 -0500, Steven Rostedt wrote:
> 
>>> ringbuffer resizing and reseting will increase the ->record_disabled
>>> and then wait until a rcu_shced grace period passes.
>>>
>>> Contrarily, testing ->record_disabled should be at the same
>>> preempt disabled critical region as writing into ringbuffer, otherwise
>>> it will leave a window break ringbuffer resizing or reseting.
>> So the resizing and the resetting need a synchronize_sched() after the
>> disabling of the buffers, right?
> 
> Looking at the code, the synchronize_sched() is already done in
> ring_buffer_resize, and the caller (trace.c:tracing_reset() ) also
> disables the ring buffer and calls synchronize_sched().
> 
> With that, what other window is still opened (after this fix)?
> 

This window is still opened: (RCU vs IDLE vs Tracing)

synchronize_sched() does not protect preempt_disable()/enable() for
idle process. But tracing(function_graph, function) introduce more
preempt_disable()/enable() for idle process. It brings windows.

I bet that this bug is not come from this window.
(I added some strict code to RCU and did stress test,
bug was still occurred.)

--
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/