On Tue 14-07-20 06:12:47, Tom Rix wrote:
>
> On 7/14/20 6:10 AM, Matthew Wilcox wrote:
> > On Tue, Jul 14, 2020 at 06:05:09AM -0700, trix@xxxxxxxxxx wrote:
> >> From: Tom Rix <trix@xxxxxxxxxx>
> >>
> >> clang static analysis flags this error
> >>
> >> inode.c:1083:5: warning: Argument to kfree() is the address of the
> >> local variable 'unf_single', which is not memory allocated by
> >> malloc() [unix.Malloc]
> >> kfree(un);
> >> ^~~~~~~~~
> >> Assignment of 'un'
> >>
> >> /*
> >> * We use this in case we need to allocate
> >> * only one block which is a fastpath
> >> */
> >> unp_t unf_single = 0;
> >>
> >> ...
> >>
> >> if (blocks_needed == 1) {
> >> un = &unf_single;
> >> } else {
> >> un = kcalloc(min(blocks_needed, max_to_insert),
> >> UNFM_P_SIZE, GFP_NOFS);
> >> if (!un) {
> >> un = &unf_single;
> >> blocks_needed = 1;
> >> max_to_insert = 0;
> >> }
> >> }
> >>
> >> The logic to free 'un'
> >>
> >> if (blocks_needed != 1)
> >> kfree(un);
> >>
> >> Because the kcalloc failure falls back to using unf_single,
> >> the if-check for the free is wrong.
> > I think you mean "Because clang's static analysis is limited, it
> > warns incorrectly about this". There's no path to get to the
> > kfree with blocks_needed != 1 and un being equal to &unf_single.
>
> Ok.
I agree with Matthew the patch will make the code more obviously correct so
it's a sensible cleanup. But the changelog needs to redone to reflect this
is just a cleanup before the patch can be merged.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
