Re: [PATCH 2/3] md/bitmap: Delete an unnecessary check before the function call "kfree"

NeilBrown
2015-02-03T09:07:38Z

[-- Attachment #1: Type: text/plain, Size: 3341 bytes --]

On Tue, 03 Feb 2015 09:48:01 +0100 walter harms <wharms@bfs.de> wrote:

>
>
> Am 02.02.2015 20:46, schrieb NeilBrown:
> > On Mon, 02 Feb 2015 16:20:42 +0100 SF Markus Elfring
> > <elfring@users.sourceforge.net> wrote:
> >
> >> From: Markus Elfring <elfring@users.sourceforge.net>
> >> Date: Mon, 2 Feb 2015 15:10:57 +0100
> >>
> >> The kfree() function tests whether its argument is NULL and then
> >> returns immediately. Thus the test around the call is not needed.
> >>
> >> * This issue was detected by using the Coccinelle software.
> >>
> >> * Let us also move an assignment for the variable "pages" to the place
> >> directly before it is really needed for a loop.
> >>
> >> * Let us also move another kfree() call into a block which should belong
> >> to a previous check for the variable "bp".
> >>
> >> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> >> ---
> >> drivers/md/bitmap.c | 10 +++++-----
> >> 1 file changed, 5 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> >> index da3604e..47d72df 100644
> >> --- a/drivers/md/bitmap.c
> >> +++ b/drivers/md/bitmap.c
> >> @@ -1586,15 +1586,15 @@ static void bitmap_free(struct bitmap *bitmap)
> >> bitmap_file_unmap(&bitmap->storage);
> >>
> >> bp = bitmap->counts.bp;
> >> - pages = bitmap->counts.pages;
> >>
> >> /* free all allocated memory */
> >> -
> >> - if (bp) /* deallocate the page memory */
> >> + if (bp) { /* deallocate the page memory */
> >> + pages = bitmap->counts.pages;
> >> for (k = 0; k < pages; k++)
> >> - if (bp[k].map && !bp[k].hijacked)
> >> + if (!bp[k].hijacked)
> >> kfree(bp[k].map);
> >> - kfree(bp);
> >> + kfree(bp);
> >> + }
> >> kfree(bitmap);
> >> }
> >>
> >
> > Hi,
> > I'm somewhat amused that you removed a test for one kfree, but imposed a
> > test on another. I realised the second test was already there, but why not
> > just:
> >
> > diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> > index da3604e73e8a..ad13b2e1bf1f 100644
> > --- a/drivers/md/bitmap.c
> > +++ b/drivers/md/bitmap.c
> > @@ -1592,7 +1592,7 @@ static void bitmap_free(struct bitmap *bitmap)
> >
> > if (bp) /* deallocate the page memory */
> > for (k = 0; k < pages; k++)
> > - if (bp[k].map && !bp[k].hijacked)
> > + if (!bp[k].hijacked)
> > kfree(bp[k].map);
> > kfree(bp);
> > kfree(bitmap);
> >
> >
> > It makes the intention of the patch much clearer.
> >
> > I'd probably prefer to leave the code as it is. I don't think either patch
> > is really an improvement in readability, and readability trumps performance
> > in places like this.
> >
>
>
> hello Neil,
> just for my curiosity.
> is it possible that a bp[k] exists but bp[k].hijacked is 0 ?
> if that case: kfree(bp) would free an object in use.
> otherwise hijacked seems useless here as it is possible to free
> everything.
>
> re,
> wh

If .hijacked is 0, the .map is a pointer (that would need to be freed) or is
NULL.
If .hijacked is 1, then .map has been re-tasked as 2 16-bit counters. They
are probably bother zero at this point, but I think it is safer to completely
skip the 'free' if 'hijacked' is set as in that case 'map' isn't a pointer.

NeilBrown

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]