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

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Date:	Sat, 12 Dec 2009 14:21:48 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Greg KH <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.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.

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?

		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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