linux-kernel - [patch] rt: res

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Date:	Thu, 12 Feb 2009 11:16:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Thomas Gleixner <tglx@...x.de>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Carsten Emde <ce@...g.ch>, Clark Williams <williams@...hat.com>
Subject: [patch] rt: res_counter fix


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> > I get some sleep while atomic warnings.
> > I've put the log and my config in attachment.
> 
> Note, it's a wicked bug: I can't reproduce it anymore.
> I would have been glad to give you an irqsoff trace but I can't :-)

i tried your config and after a few bootups the warning did trigger.

It's the new resource counter code. The IRQ flags disabling it does
seems a bit dubious to me. Peter, what do you think?

Frederic, could you try the patch below?

	Ingo

----------->
Subject: rt: res_counter fix
From: Ingo Molnar <mingo@...e.hu>
Date: Thu Feb 12 11:11:47 CET 2009

Frederic Weisbecker reported this warning:

[   45.228562] BUG: sleeping function called from invalid context at kernel/rtmutex.c:683
[   45.228571] in_atomic(): 0, irqs_disabled(): 1, pid: 4290, name: ntpdate
[   45.228576] INFO: lockdep is turned off.
[   45.228580] irq event stamp: 0
[   45.228583] hardirqs last  enabled at (0): [<(null)>] (null)
[   45.228589] hardirqs last disabled at (0): [<ffffffff8025449d>] copy_process+0x68d/0x1500
[   45.228602] softirqs last  enabled at (0): [<ffffffff8025449d>] copy_process+0x68d/0x1500
[   45.228609] softirqs last disabled at (0): [<(null)>] (null)
[   45.228617] Pid: 4290, comm: ntpdate Tainted: G        W  2.6.29-rc4-rt1-tip #1
[   45.228622] Call Trace:
[   45.228632]  [<ffffffff8027dfb0>] ? print_irqtrace_events+0xd0/0xe0
[   45.228639]  [<ffffffff8024cd73>] __might_sleep+0x113/0x130
[   45.228646]  [<ffffffff8077c811>] rt_spin_lock+0xa1/0xb0
[   45.228653]  [<ffffffff80296a3d>] res_counter_charge+0x5d/0x130
[   45.228660]  [<ffffffff802fb67f>] __mem_cgroup_try_charge+0x7f/0x180
[   45.228667]  [<ffffffff802fc407>] mem_cgroup_charge_common+0x57/0x90
[   45.228674]  [<ffffffff80212096>] ? ftrace_call+0x5/0x2b
[   45.228680]  [<ffffffff802fc49d>] mem_cgroup_newpage_charge+0x5d/0x60
[   45.228688]  [<ffffffff802d94ce>] __do_fault+0x29e/0x4c0
[   45.228694]  [<ffffffff8077c843>] ? rt_spin_unlock+0x23/0x80
[   45.228700]  [<ffffffff802db8b5>] handle_mm_fault+0x205/0x890
[   45.228707]  [<ffffffff80212096>] ? ftrace_call+0x5/0x2b
[   45.228714]  [<ffffffff8023495e>] do_page_fault+0x11e/0x2a0
[   45.228720]  [<ffffffff8077e5a5>] page_fault+0x25/0x30
[   45.228727]  [<ffffffff8043e1ed>] ? __clear_user+0x3d/0x70
[   45.228733]  [<ffffffff8043e1d1>] ? __clear_user+0x21/0x70

The reason is the raw IRQ flag use of kernel/res_counter.c.

The irq flags tricks there seem a bit pointless: it cannot
protect the c->parent linkage because local_irq_save() is
only per CPU.

So replace it with _nort(). This code needs a second look.

Reported-by: Frederic Weisbecker <fweisbec@...il.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/res_counter.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: tip/kernel/res_counter.c
===================================================================
--- tip.orig/kernel/res_counter.c
+++ tip/kernel/res_counter.c
@@ -43,7 +43,7 @@ int res_counter_charge(struct res_counte
 	struct res_counter *c, *u;
 
 	*limit_fail_at = NULL;
-	local_irq_save(flags);
+	local_irq_save_nort(flags);
 	for (c = counter; c != NULL; c = c->parent) {
 		spin_lock(&c->lock);
 		ret = res_counter_charge_locked(c, val);
@@ -62,7 +62,7 @@ undo:
 		spin_unlock(&u->lock);
 	}
 done:
-	local_irq_restore(flags);
+	local_irq_restore_nort(flags);
 	return ret;
 }
 
@@ -79,13 +79,13 @@ void res_counter_uncharge(struct res_cou
 	unsigned long flags;
 	struct res_counter *c;
 
-	local_irq_save(flags);
+	local_irq_save_nort(flags);
 	for (c = counter; c != NULL; c = c->parent) {
 		spin_lock(&c->lock);
 		res_counter_uncharge_locked(c, val);
 		spin_unlock(&c->lock);
 	}
-	local_irq_restore(flags);
+	local_irq_restore_nort(flags);
 }
 
 
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