linux-kernel - Re: [PATCH] generic-ipi: add lock context annotations

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Date:	Tue, 23 Nov 2010 12:40:16 +0300
From:	Dan Carpenter <error27@...il.com>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Namhyung Kim <namhyung@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] generic-ipi: add lock context annotations

On Tue, Nov 23, 2010 at 09:49:56AM +0100, Jens Axboe wrote:
> I guess what Peter means is that the fact that the function grabs the
> lock is apparent in the code, if sparse was a bit "smarter", it would
> see and note this itself.

The sparse warning messages should have been included in the commit
message.  Here they are:

kernel/smp.c:513:6: warning: context imbalance in 'ipi_call_lock' - wrong count at exit
kernel/smp.c:518:6: warning: context imbalance in 'ipi_call_unlock' - unexpected unlock
kernel/smp.c:523:6: warning: context imbalance in 'ipi_call_lock_irq' - wrong count at exit
kernel/smp.c:528:6: warning: context imbalance in 'ipi_call_unlock_irq' - unexpected unlock

What happens is that sparse *does* see that the locks are unlocked and
that's what it complains about.

Sparse works before the code is linked so this change doesn't affect
anything outside kernel/smp.c.  If we added these annotations to
include/linux/smp.h then they would be used for checking
kernel/smpboot.c

regards,
dan carpenter

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