linux-kernel - Re: [GIT PATCH] TTY patches for 2.6.33-git

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Date:	Sat, 12 Dec 2009 22:48:41 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Greg KH <gregkh@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PATCH] TTY patches for 2.6.33-git

On Sat, 12 Dec 2009, Alan Cox wrote:
> > I think we could possibly add a "__might_sleep()" to _lock_kernel(). It 
> > doesn't really sleep, but it's invalid to take the kernel lock in an 
> > atomic region, so __might_sleep() might be the right thing anyway.
> 
> It's only invalid if you don't already hold the lock. The old tty code
> worked because every path into tty_fasync already held the lock ! That
> specific case - taking it the first time should definitely
> __might_sleep().
> 
> Mind you it's probably still rather dumb and would be a good debugging
> aid for -next to be able to warn on all offences if only to catch this
> stuff for the future BKL removal work.

Just patched the following in and it catched your problem nicely. With
your AB/BA fix patch applied everything is fine.

Thanks,

	tglx
---
Subject: BKL: Add might sleep to __lock_kernel
From: Thomas Gleixner <tglx@...utronix.de>
Date: Sat, 12 Dec 2009 20:29:00 +0100

Catches all offenders which take the BKL first time in an atomic
region. Recursive lock_kernel calls are not affected.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 lib/kernel_lock.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6/lib/kernel_lock.c
===================================================================
--- linux-2.6.orig/lib/kernel_lock.c
+++ linux-2.6/lib/kernel_lock.c
@@ -64,6 +64,8 @@ void __lockfunc __release_kernel_lock(vo
 #ifdef CONFIG_PREEMPT
 static inline void __lock_kernel(void)
 {
+	might_sleep();
+
 	preempt_disable();
 	if (unlikely(!_raw_spin_trylock(&kernel_flag))) {
 		/*
--
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