linux-kernel - Re: [PATCH] markers: fix unregister bug and reenter bug

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Date:	Mon, 29 Sep 2008 10:27:22 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] markers: fix unregister bug and reenter bug


* Lai Jiangshan <laijs@...fujitsu.com> wrote:

> unregister bug:
> 
> codes using makers are typically calling marker_probe_unregister()
> and then destroying the data that marker_probe_func needs(or
> unloading this module). This is bug when the corresponding
> marker_probe_func is still running(on other cpus),
> it is using the destroying/ed data.
> 
> we should call synchronize_sched() after marker_update_probes().
> 
> reenter bug:
> 
> marker_probe_register(), marker_probe_unregister() and
> marker_probe_unregister_private_data() are not reentrant safe
> functions. these 3 functions release markers_mutex and then
> require it again and do "entry->oldptr = old; ...", but entry->oldptr
> maybe is using now for these 3 functions may reenter when markers_mutex
> is released.
> 
> we use synchronize_sched() instead of call_rcu_sched() to fix
> this bug. actually we can do:
> "
> if (entry->rcu_pending)
> 		rcu_barrier_sched();
> "
> after require markers_mutex again. but synchronize_sched()
> is better and simpler. For these 3 functions are not critical path.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>

applied to tip/tracing/markers, thanks!

Mathieu, i've reactivated tip/tracing/markers for linux-next 
integration, it propagates into auto-ftrace-next. Tracepoints are what 
we use in the scheduler/etc. in tip/master, but until there's marker use 
elsewhere there's no reason not to apply fix patches.

	Ingo
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