Hi Andrew,
On Mon, Apr 20, 2020 at 10:42:10PM -0700, Andrew Morton wrote:
> On Tue, 14 Apr 2020 08:02:27 -0700 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> >
> > Use the new readahead operation in erofs.
> >
>
> Well this is exciting.
>
> fs/erofs/data.c: In function erofs_raw_access_readahead:
> fs/erofs/data.c:149:18: warning: last_block may be used uninitialized in this function [-Wmaybe-uninitialized]
> *last_block + 1 != current_block) {
>
> It seems to be a preexisting bug, which your patch prompted gcc-7.2.0
> to notice.
>
> erofs_read_raw_page() goes in and uses *last_block, but neither of its
> callers has initialized it. Could the erofs maintainers please take a
> look?
simply because last_block doesn't need to be initialized at first,
because bio == NULL in the begining anyway. I believe this is a gcc
false warning because some gcc versions raised some before (many gccs
don't, including my current gcc (Debian 8.3.0-6) 8.3.0).
in detail,
146 /* note that for readpage case, bio also equals to NULL */
147 if (bio &&
148 /* not continuous */
149 *last_block + 1 != current_block) {
150 submit_bio_retry:
151 submit_bio(bio);
152 bio = NULL;
153 }
bio will be NULL and will bypass the next condition at first.
after that,
155 if (!bio) {
...
221 bio = bio_alloc(GFP_NOIO, nblocks);
...
}
...
230 err = bio_add_page(bio, page, PAGE_SIZE, 0);
231 /* out of the extent or bio is full */
232 if (err < PAGE_SIZE)
233 goto submit_bio_retry;
234
235 *last_block = current_block;
so bio != NULL, and last_block will be assigned then as well.
Thanks,
Gao Xiang
