linux-kernel - Re: [PATCH] netpoll: Fix carrier detection for drivers that are using phylib

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Message-Id: <1247149862.12784.6.camel@twins>
Date:	Thu, 09 Jul 2009 16:31:02 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Anton Vorontsov <avorontsov@...mvista.com>,
	Andrew Morton <akpm@...ux-foundation.org>, oleg@...hat.com,
	mingo@...e.hu, linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] netpoll: Fix carrier detection for drivers that are
 using phylib

On Thu, 2009-07-09 at 09:18 -0500, Matt Mackall wrote:
> 
> Sorry if I was unclear. I'm suggesting setting the count so the existing
> PREEMPT_ACTIVE test here fires:
> 
> int __sched _cond_resched(void)
> {
>         if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
>                                         system_state == SYSTEM_RUNNING) {
>                 __cond_resched();
>                 return 1;
>         }
>         return 0;
> }

Right, /me read preempt and thought a simple preempt inc but didn't read
the code. Shame on me.

So something like (utterly untested and such)

---

 arch/x86/include/asm/thread_info.h |    2 +-
 kernel/sched.c                     |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index b078352..7b5dbce 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -49,7 +49,7 @@ struct thread_info {
 	.exec_domain	= &default_exec_domain,	\
 	.flags		= 0,			\
 	.cpu		= 0,			\
-	.preempt_count	= 1,			\
+	.preempt_count	= 1 + PREEMPT_ACTIVE,	\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
diff --git a/kernel/sched.c b/kernel/sched.c
index fd3ac58..8e81162 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6599,8 +6599,7 @@ static void __cond_resched(void)
 
 int __sched _cond_resched(void)
 {
-	if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
-					system_state == SYSTEM_RUNNING) {
+	if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE)) {
 		__cond_resched();
 		return 1;
 	}
@@ -9422,6 +9421,7 @@ void __init sched_init(void)
 	perf_counter_init();
 
 	scheduler_running = 1;
+	sub_preempt_count(PREEMPT_ACTIVE);
 }
 
 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP


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