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

From: Vivek Goyal <vgoyal@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: nigel@nigel.suspend2.net,
	Kexec Mailing List <kexec@lists.infradead.org>,
	linux-kernel@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
	Pavel Machek <pavel@ucw.cz>, Huang Ying <ying.huang@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	mingo@elte.hu
Subject: Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock, 0) in kernel_kexec()
Date: Wed, 13 Aug 2008 14:31:56 -0400	[thread overview]
Message-ID: <20080813183156.GA20974@redhat.com> (raw)
In-Reply-To: <m1r68shjhb.fsf@frodo.ebiederm.org>

On Wed, Aug 13, 2008 at 11:12:48AM -0700, Eric W. Biederman wrote:
> Linus Torvalds <torvalds@linux-foundation.org> writes:
> 
> > On Wed, 13 Aug 2008, Huang Ying wrote:
> >>
> >> -	xchg(&kexec_lock, 0);
> >> +	locked = xchg(&kexec_lock, 0);
> >> +	BUG_ON(!locked);
> >
> > Why do you want to do this at all? 
> >
> > And why do you implement your locks with xchg() in the first place? That's 
> > total and utter crap.
> >
> > Hint: we have _real_ locking primitives in the kernel.
> 
> This part certainly.
> 
> The way the code should work, and the way it has in the past is:
> image = xchg(&kexec_image, NULL)
> if (!image)
>    return -EINVAL;
> 
> Very simple and very obvious and very easy to get right, and it has
> been that way for years.
> 

Hi Eric,

Are there any issues with usage of test_and_set_bit() or usage of spinlock
primitives?

Thanks
Vivek

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