On Thu, Sep 05, 2013 at 01:38:48AM +0000, Linux Kernel wrote:
> Gitweb: http://git.kernel.org/linus/;a=commit;h=107a7bd31ac003e42c0f966aa8e5b26947de6024
> Commit: 107a7bd31ac003e42c0f966aa8e5b26947de6024
> Parent: 3be78c73179c9347bdc0a92b2898063bd2300ff7
> Author: Theodore Ts'o <[email protected]>
> AuthorDate: Fri Aug 16 21:23:41 2013 -0400
> Committer: Theodore Ts'o <[email protected]>
> CommitDate: Fri Aug 16 21:23:41 2013 -0400
>
> ext4: cache all of an extent tree's leaf block upon reading
> + * ext4_es_cache_extent() inserts information into the extent status
> + * tree if and only if there isn't information about the range in
> + * question already.
> + */
> +void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
> + ext4_lblk_t len, ext4_fsblk_t pblk,
> + unsigned int status)
> +{
> + struct extent_status *es;
> + struct extent_status newes;
> + ext4_lblk_t end = lblk + len - 1;
> +
> + newes.es_lblk = lblk;
> + newes.es_len = len;
> + ext4_es_store_pblock(&newes, pblk);
ext4_es_store_pblock or's the pblk with the existing contents of the struct member.
(albeit masked with ES_MASK)
Should there be a
newes.es_pblk = 0;
up there too ?
It seems like if the stack happened to contain any of ES_WRITTEN | ES_UNWRITTEN | ES_DELAYED | ES_HOLE
then it could leak through into the new extent status.
Dave
On Thu, Sep 05, 2013 at 10:37:49AM -0400, Dave Jones wrote:
> > +void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
> > + ext4_lblk_t len, ext4_fsblk_t pblk,
> > + unsigned int status)
> > +{
> > + struct extent_status *es;
> > + struct extent_status newes;
> > + ext4_lblk_t end = lblk + len - 1;
> > +
> > + newes.es_lblk = lblk;
> > + newes.es_len = len;
> > + ext4_es_store_pblock(&newes, pblk);
>
>
> ext4_es_store_pblock or's the pblk with the existing contents of the struct member.
> (albeit masked with ES_MASK)
>
> Should there be a
>
> newes.es_pblk = 0;
>
> up there too ?
The next line after ext4_es_store_pblock() is:
ext4_es_store_status(&newes, status);
This will set remaining ES_WRITTEN | ES_UNWRITTEN... bits.
So the only reason to add a line explicitly setting es_pblk to zero
would be to suppress a warning from some insufficiently smart static
code analysis tool. I didn't see a warning from gcc, but it's
possible that this is something which is causing Coverity or some
other code scanner heartburn.
Cheers,
- Ted
On Thu, Sep 05, 2013 at 10:53:34AM -0400, Theodore Ts'o wrote:
> > ext4_es_store_pblock or's the pblk with the existing contents of the struct member.
> > (albeit masked with ES_MASK)
> >
> > Should there be a
> >
> > newes.es_pblk = 0;
> >
> > up there too ?
>
> The next line after ext4_es_store_pblock() is:
>
> ext4_es_store_status(&newes, status);
>
> This will set remaining ES_WRITTEN | ES_UNWRITTEN... bits.
>
> So the only reason to add a line explicitly setting es_pblk to zero
> would be to suppress a warning from some insufficiently smart static
> code analysis tool. I didn't see a warning from gcc, but it's
> possible that this is something which is causing Coverity or some
> other code scanner heartburn.
Yep, that's what picked it up. I'll add a 'not a bug' annotation to stop
it getting flagged again. This was the only ext* issue that Coverity
picked up from yesterdays merge btw, which I guess is good news ;)
Dave
On Thu, Sep 05, 2013 at 11:14:57AM -0400, Dave Jones wrote:
> > So the only reason to add a line explicitly setting es_pblk to zero
> > would be to suppress a warning from some insufficiently smart static
> > code analysis tool. I didn't see a warning from gcc, but it's
> > possible that this is something which is causing Coverity or some
> > other code scanner heartburn.
>
> Yep, that's what picked it up. I'll add a 'not a bug' annotation to stop
> it getting flagged again. This was the only ext* issue that Coverity
> picked up from yesterdays merge btw, which I guess is good news ;)
Indeed.
Hmm... I could add a new inline function
"ext4_es_store_pblock_status()" which sets both parts of the es_pblk
word at once, and which doesn't depend looking at its original value
at all. I doubt we would never measure a difference in performance,
but in theory it would be more efficient. And if it eliminates a
potential static code analysis complaint, maybe the two justifications
is good enough to add the new function.
Thanks for checking the coverity results!!
- Ted