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

[David Sterba <dsterba@suse.cz>]

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.

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.