linux-kernel - Re: [patch 0/6] rcu head debugobjects

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Date:	Sat, 27 Mar 2010 15:46:06 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, laijs@...fujitsu.com,
	dipankar@...ibm.com, josh@...htriplett.org, dvhltc@...ibm.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, adobriyan@...il.com
Subject: Re: [patch 0/6] rcu head debugobjects

On Sat, Mar 27, 2010 at 11:32:33AM -0400, Mathieu Desnoyers wrote:
> Hi,
> 
> Here is an updated version of the rcu head debugobjects, following the comments
> I received in the last rounds.
> 
> It applies on top of -tip, based on 2.6.34-rc2, commit
> 2e958f219d2b8d192d44e2472a214b3a93c44673
> 
> Unless people have any objection, it should be ready to be merged. I think the
> appropriate maintainer to perform this merge would be Paul E. McKenney, because
> this patchset is RCU-related.

This should be very helpful in tracking down otherwise-painful bugs!!!
Thank you, Mathieu!!!  I am happy to apply this, especially given Dave
Miller's Acked-by.

A few questions and comments:

o	Patches 1/6, 2/6, 3/6: Was the intent for the three Subject
	lines to read as follows?

	[patch 1/6] Revert "net: remove INIT_RCU_HEAD() usage"
	[patch 2/6] Revert "netfilter: don't use INIT_RCU_HEAD()"
	[patch 3/6] Revert "net: don't use INIT_RCU_HEAD"

o	Patch 4/6 looks good to me, and given that Thomas hasn't
	complained, I am guessing that he is OK with it.

o	Would it be possible to make this bisectable as follows?

	a.	Insert a new patch after current patch 4/6 that
		defines destroy_rcu_head_on_stack(),
		rcu_head_init_on_stack(), and rcu_head_init() with
		their !CONFIG_DEBUG_OBJECTS_RCU_HEAD definitions.

	b.	Move current patch 6/6 to this position.

	c.	Move current patch 5/6 to this position, updating
		to reflect the new patch added in (a) above.

o	Patch 6/6: Would it be possible to use the object_is_on_stack()
	function defined in include/linux/sched.h instead of passing
	in the flag on_stack to bdi_work_init()?  It looks like
	fs/fs-writeback.c already includes include/linux/sched.h, so
	shouldn't be a problem from a #include-hell viewpoint.

Please let me know if I am missing something on any of the above.  If
these changes seem reasonable to you, please either submit a new patch
set or let me know that you are OK with me making these changes.

							Thanx, Paul
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