linux-kernel - Re: [PATCH 7/7] uprobes: kill uprobes_srcu/uprobe_srcu

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Message-ID: <1338332687.26856.189.camel@twins>
Date:	Wed, 30 May 2012 01:04:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [PATCH 7/7] uprobes: kill uprobes_srcu/uprobe_srcu_id

On Tue, 2012-05-29 at 21:30 +0200, Oleg Nesterov wrote:
> Kill the no longer needed uprobes_srcu/uprobe_srcu_id code.
> 
> It doesn't really work anyway. synchronize_srcu() can only synchronize
> with the code "inside" the srcu_read_lock/srcu_read_unlock section,
> while uprobe_pre_sstep_notifier() does srcu_read_lock() _after_ we
> already hit the breakpoint.
> 
> I guess this probably works "in practice". synchronize_srcu() is slow
> and it implies synchronize_sched(), and the probed task enters the non-
> preemptible section at the start of exception handler. Still this is not
> right at least in theory, and task->uprobe_srcu_id blows task_struct.

This kills the only user of srcu_read_{,un}lock_raw(), so I guess we
could also make:

  9ceae0e2
  101db7b4
  0c53dd8b

go away.. 
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