linux-kernel - Re: A question about sparse: how to use __acquires() and _

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Message-ID: <e2e108260812040412j1f3f353bv2834750dbe914c48@mail.gmail.com>
Date:	Thu, 4 Dec 2008 13:12:58 +0100
From:	"Bart Van Assche" <bart.vanassche@...il.com>
To:	"kernel list" <linux-kernel@...r.kernel.org>
Cc:	"Vladislav Bolkhovitin" <vst@...b.net>,
	"Alexander Shishkin" <alexander.shishckin@...il.com>,
	"Johannes Berg" <johannes@...solutions.net>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>
Subject: Re: A question about sparse: how to use __acquires() and __releases() correctly ?

[ping]

Is there anyone who can help me with the question below ?

Thanks,

Bart.

On Tue, Dec 2, 2008 at 8:59 PM, Bart Van Assche
<bart.vanassche@...il.com> wrote:
> Hello,
>
> I'm helping to prepare the SCST source code for inclusion in the Linux
> kernel by a.o. cleaning up sparse warnings. Although most of the SCST
> source code has been annotated by this time it's still not clear to me
> how to use __acquires() and __releases() correctly.
>
> I will illustrate my questions via the following code from
> net/core/dev.c, Linux kernel version 2.6.27.7:
>
> void dev_seq_stop(struct seq_file *seq, void *v)
>        __releases(dev_base_lock)
> {
>        read_unlock(&dev_base_lock);
> }
>
> The command "make C=2 M=net/core" produces the following output for
> the above function (using a sparse binary built from the sparse git
> repository, last updated on August 26, 2008):
>
> net/core/dev.c:2579:2: warning: context problem in 'dev_seq_stop':
> '_read_unlock' expected different context
> net/core/dev.c:2579:2:    context 'lock': wanted >= 1, got 0
>
> My questions are as follows:
> * Which argument type should be passed to __releases() -- a pointer to
> a lock structure or the lock strucure itself ? In the header file
> include/linux/spinlock_api_smp.h a pointer is passed to __acquires()
> and __releases(), while other code (like the above) passes the lock
> structure itself to the __acquires() and __releases() annotations.
> * If the __releases() annotation is used correctly in net/core/dev.c,
> why does sparse complain about a context problem ?
>
> Please keep me in CC -- I'm not subscribed to the LKML.
>
> Bart.
>
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