Re: Sparse Warnings about locks in extent-tree.c

[Liu Bo <bo.li.liu@oracle.com>]

On Tue, Sep 23, 2014 at 04:01:41PM +0200, David Sterba wrote:
> On Tue, Sep 23, 2014 at 02:45:44PM +0800, Liu Bo wrote:
> > On Mon, Sep 22, 2014 at 09:57:35PM -0400, nick wrote:
> > > Hello Btfs Developers,
> > > I am new so am unsure of how to fix this but we are hitting some sparse warnings about unlock/lock is having 
> > > a wrong count when exiting certain functions in extent-tree.c. I will paste the warnings below for you guys.
> > > Hope this is of help.
> > > Cheers,
> > > Nick  
> > > fs/btrfs/extent-tree.c:6386:39: warning: context imbalance in 'btrfs_lock_cluster' - wrong count at exit
> > > fs/btrfs/extent-tree.c:6663:44: warning: context imbalance in 'find_free_extent' - unexpected unlock
> > > fs/btrfs/extent-tree.c:8810:9: warning: context imbalance in 'btrfs_put_block_group_cache' - wrong count at exit
> > 
> > What program is producing these warning?  It looks like a static code analysis
> > tool or something.
> 
> https://sparse.wiki.kernel.org/index.php/Main_Page
> 
> It understands a few semantics like the locking and reports when there's
> an unannotated function that has imbalanced locking, like the errors
> above.

Cool, thanks Dave.

-liubo

> 
> Any static analyzer has some ratio of false positives so not every
> report means there's a bug. One would expect that a function
> 'btrfs_lock_cluster' would act as a lock and leaves some locks held at
> exit. The "fix" is to annotate it a after review.