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

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Date:	Tue, 29 May 2012 18:51:57 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, 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
Subject: Re: [PATCH 7/7] uprobes: kill uprobes_srcu/uprobe_srcu_id

On Wed, May 30, 2012 at 01:04:47AM +0200, Peter Zijlstra wrote:
> 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.. 

If it is still unused in a few months, I will get rid of them.

							Thanx, Paul

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