linux-kernel - Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock, 0) in kernel

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Date:	Wed, 13 Aug 2008 12:50:57 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>, ying.huang@...el.com,
	pavel@....cz, nigel@...el.suspend2.net, rjw@...k.pl,
	vgoyal@...hat.com, mingo@...e.hu, linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org
Subject: Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock,
 0) in kernel_kexec()



On Wed, 13 Aug 2008, Andrew Morton wrote:
> - * in interrupt context :)
> + * Return true if we acquired the lock
>   */
> -static int kexec_lock;
> +static inline bool kexec_trylock(void)
> +{
> +	return !test_and_set_bit(0, &kexec_bitlock);

Nope. That needs to be an "unsigned long".

But more importantl, why not just make it a lock in the first place?

	static DEFINE_SPINLOCK(kexec_lock);

	#define kexec_trylock() spin_trylock(&kexec_lock)
	#define kexec_unlock() spin_unlock(&kexec_lock)

and then you get it all right and clear and obvious.

Yeah, and I didn't check whether there is anything that is supposed to be 
able to sleep. If there is, use a mutex instead of a spinlock, of course.

		Linus
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