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

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Date:	Sat, 12 Dec 2009 23:33:15 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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, Linus Torvalds wrote:
 
> 
> 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.
> 
> True.
> 
> > 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().
> 
> That would give us at least somewhat better debugging. And it's a very 
> natural thing to do. IOW, just something like the appended.
> 
> But maybe it complains about valid (but unusual) things. For example, it's 
> not strictly speaking _wrong_ to take the kernel lock while preemption is 
> disabled, even though it's a really bad idea.
> 
> Anybody willing to be the guinea-pig?

Replaced my patch with yours and it works the same way (except for the
PREEMPT=n case)

Acked-and-Tested-by: Thomas Gleixner <tglx@...utronix.de>
 
> 		Linus
> 
> ---
>  lib/kernel_lock.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c
> index 4ebfa5a..5526b46 100644
> --- a/lib/kernel_lock.c
> +++ b/lib/kernel_lock.c
> @@ -122,8 +122,10 @@ void __lockfunc _lock_kernel(const char *func, const char *file, int line)
>  
>  	trace_lock_kernel(func, file, line);
>  
> -	if (likely(!depth))
> +	if (likely(!depth)) {
> +		might_sleep();
>  		__lock_kernel();
> +	}
>  	current->lock_depth = depth;
>  }
>  
> 
--
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