Re: [PATCH] m32r: Revise __raw_read_trylock()
From: Matthew Wilcox
Date: Tue Sep 26 2006 - 18:30:20 EST
On Tue, Sep 26, 2006 at 02:33:44PM -0700, Andrew Morton wrote:
> We don't have a changelog for this patch. My usual technique when this
> happens is to mutter something unprintable then go on a hunt through the
> mailing list archives.
> But all I have is "Matthew Wilcox pointed out that
> generic__raw_read_trylock() is unfit for use.".
> What's wrong with it?
I pointed it out on linux-arch a couple of weeks ago. Ever look at the
$ git-diff linus spinlock.c
diff --git a/kernel/spinlock.c b/kernel/spinlock.c
index fb524b0..6fc4c92 100644
@@ -16,17 +16,6 @@ #include <linux/interrupt.h>
- * Generic declaration of the raw read_trylock() function,
- * architectures are supposed to optimize this:
-int __lockfunc generic__raw_read_trylock(raw_rwlock_t *lock)
- return 1;
If the cpu has the lock held for write, is interrupted, and the interrupt
handler calls read_trylock(), it's an instant deadlock.
Now, Dave Miller has subsequently pointed out that we don't have any
situations where this can occur. Nevertheless, we should delete
generic__raw_read_lock (and its associated EXPORT to make Arjan happy)
so that nobody thinks they can use it.
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