linux-kernel - Re: [PATCH] kmemleak: Fix scheduling-while-atomic bug

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Date:	Thu, 02 Jul 2009 10:48:28 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	git-commits-head@...r.kernel.org
Subject: Re: [PATCH] kmemleak: Fix scheduling-while-atomic bug

On Wed, 2009-07-01 at 11:30 +0200, Ingo Molnar wrote:
> * Catalin Marinas <catalin.marinas@....com> wrote:
> 
> > > The minimal fix below removes scan_yield() and adds a 
> > > cond_resched() to the outmost (safe) place of the scanning 
> > > thread. This solves the regression.
> > 
> > With CONFIG_PREEMPT disabled it won't reschedule during the bss 
> > scanning but I don't see this as a real issue (task stacks 
> > scanning probably takes longer anyway).
> 
> Yeah. I suspect one more cond_resched() could be added - i just 
> didnt see an obvious place for it, given that scan_block() is being 
> called with asymetric held-locks contexts.

Now that your patch was merged, I propose adding a few more
cond_resched() calls, useful for the !PREEMPT case:


kmemleak: Add more cond_resched() calls in the scanning thread

From: Catalin Marinas <catalin.marinas@....com>

Following recent patch to no longer reschedule in the scan_block()
function, we need a few more cond_resched() calls in the kmemleak_scan()
function (useful if PREEMPT is disabled).

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
 mm/kmemleak.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 013f188..b4f675e 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -932,13 +932,16 @@ static void kmemleak_scan(void)
 
 	/* data/bss scanning */
 	scan_block(_sdata, _edata, NULL);
+	cond_resched();
 	scan_block(__bss_start, __bss_stop, NULL);
 
 #ifdef CONFIG_SMP
 	/* per-cpu sections scanning */
-	for_each_possible_cpu(i)
+	for_each_possible_cpu(i) {
+		cond_resched();
 		scan_block(__per_cpu_start + per_cpu_offset(i),
 			   __per_cpu_end + per_cpu_offset(i), NULL);
+	}
 #endif
 
 	/*
@@ -960,6 +963,7 @@ static void kmemleak_scan(void)
 			/* only scan if page is in use */
 			if (page_count(page) == 0)
 				continue;
+			cond_resched();
 			scan_block(page, page + 1, NULL);
 		}
 	}
@@ -969,6 +973,7 @@ static void kmemleak_scan(void)
 	 * not enabled by default.
 	 */
 	if (kmemleak_stack_scan) {
+		cond_resched();
 		read_lock(&tasklist_lock);
 		for_each_process(task)
 			scan_block(task_stack_page(task),


-- 
Catalin

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