linux-kernel - Re: 3.0.23-rt39 BUG: scheduling while atomic, _cpu

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: <1331344992.25686.612.camel@gandalf.stny.rr.com>
Date:	Fri, 09 Mar 2012 21:03:12 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	frank.rowand@...sony.com
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: 3.0.23-rt39 BUG: scheduling while atomic, _cpu_down()

On Fri, 2012-03-09 at 17:51 -0800, Frank Rowand wrote:
> Hi Thomas,
> (and Steve, since you've been mucking about in the hotplug code,)
> 
> Yet another bit of fallout related to hotplug.
> 
> This appears to affect 3.0-rt1, 3.0.23-rt29, and 3.2.9-rt17.
> (Thus probably all 3.x versions, but I haven't been masochistic
> enough to check.)
> 
> If not defined CONFIG_PREEMPT_RT_FULL then

So you're saying that there's a bug with PREEMPT_RT off?

> 
>   - hotplug_lock() is a mutex_lock()
>   - cpu_hotplug_begin() calls hotplug_lock()
>   - _cpu_down() calls cpu_hotplug_begin() with preemption
>     disabled (disabled by the migrate_disable())
> 
> The call to cpu_hotplug_begin() is not in a preempt disabled
> region until hotplug-use-migrate-disable.patch.  This patch
> moves the preempt_enable() (aka migrate_enable()) from just
> before calling cpu_hotplug_begin() to after "out_cancel:".
> 
> The BUG can be triggered by:
> 
>    echo 0 > /sys/devices/system/cpu/cpu1/online 

Note, there's a lot more wrong with hotplug in rt than this. The hotplug
code really needs a total rewrite for RT to work with it. It probably
should have a total rewrite in mainline anyway.

-- Steve


--
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/