From: Oleg Nesterov <oleg@redhat.com>
To: Roland McGrath <roland@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
peterz@infradead.org, efault@gmx.de, rjw@sisk.pl,
jdike@addtoit.com, mingo@elte.hu,
user-mode-linux-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: Re: [patch] fix uml slowness caused by ptrace preemption bug on host
Date: Fri, 20 Mar 2009 14:51:47 +0100 [thread overview]
Message-ID: <20090320135147.GA20965@redhat.com> (raw)
In-Reply-To: <20090319233311.8B26BFC381@magilla.sf.frob.com>
On 03/19, Roland McGrath wrote:
>
> I'm no scheduler expert and I don't know whether the exact placement in
> your change is the optimal one.
Agreed, can't we do a bit more simple patch?
--- kernel/signal.c
+++ kernel/signal.c
@@ -1572,8 +1572,10 @@ static void ptrace_stop(int exit_code, i
spin_unlock_irq(¤t->sighand->siglock);
read_lock(&tasklist_lock);
if (may_ptrace_stop()) {
+ preempt_disable();
do_notify_parent_cldstop(current, CLD_TRAPPED);
read_unlock(&tasklist_lock);
+ preempt_enable_no_resched();
schedule();
} else {
/*
Yes, the task can be preempted right after spin_unlock(->siglock), but
this is unlikely. We need the "synchronous" wakeup, and this patch helps
as well.
Actually, I don't know which ptrace requests really need to make sure
the tracee was deactivated. Perhaps they can call wait_task_inactive()
themselves? I guess this is bad idea, but most of requests definitely
do not need wait_task_inactive().
Oleg.
next prev parent reply other threads:[~2009-03-20 13:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-19 22:23 [patch] fix uml slowness caused by ptrace preemption bug on host Miklos Szeredi
2009-03-19 23:33 ` Roland McGrath
2009-03-20 8:05 ` Miklos Szeredi
2009-03-20 14:04 ` Oleg Nesterov
2009-03-20 14:04 ` [uml-devel] " Oleg Nesterov
2009-03-20 13:51 ` Oleg Nesterov [this message]
2009-03-20 8:19 ` Peter Zijlstra
2009-03-20 8:27 ` Miklos Szeredi
2009-03-20 8:30 ` Ingo Molnar
2009-03-20 8:30 ` [uml-devel] " Ingo Molnar
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