linux-kernel - [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu

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Date:	Fri, 6 Apr 2012 00:20:24 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Anton Arapov <anton@...hat.com>
Subject: [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu_id

Hello.

Not for inclusion yet, only for the early review.

I didn't even try to test these changes, and I am not expert
in this area. And even _if_ this code is correct, I need to
re-split these changes anyway, update the changelogs, etc.

Questions:

	- does it make sense?

	- can it work or I missed something "in general" ?

Why:

	- It would be nice to remove a member from task_struct.

	- Afaics, the usage of uprobes_srcu does not look right,
	  at least in theory, see 6/6.

	  The comment above delete_uprobe() says:

	  	The current unregistering thread waits till all
	  	other threads have hit a breakpoint, to acquire
	  	the uprobes_treelock before the uprobe is removed
	  	from the rbtree.

	  but synchronize_srcu() can only help if a thread which
	  have hit the breakpoint has already called srcu_read_lock().
	  It can't synchronize with read_lock "in future", and there
	  is a small window.

	  We could probably add another synchronize_sched() before
	  synchronize_srcu(), but this doesn't look very nice and

	- I am not sure yet, but perhaps with these changes we can
	  also kill mm->uprobes_state.count.

Any review is very much appreciated.

Oleg.

 include/linux/sched.h   |    1 -
 kernel/events/uprobes.c |  117 ++++++++++++++++++++++++++++++-----------------
 2 files changed, 75 insertions(+), 43 deletions(-)

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