Re: A question about sparse: how to use __acquires() and __releases() correctly ?

From: Bart Van Assche
Date: Thu Dec 04 2008 - 07:13:19 EST


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



On Tue, Dec 2, 2008 at 8:59 PM, Bart Van Assche
<bart.vanassche@xxxxxxxxx> 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
> 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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