Re: [PATCH 6.5 211/285] btrfs: scrub: fix grouping of read IO

On 2023-10-26 15:31, Sam James wrote:

'btrfs: scrub: fix grouping of read IO' seems to intorduce a -Wmaybe-uninitialized warning (which becomes fatal with the kernel's passed -Werror=...) with 6.5.9:

/var/tmp/portage/sys-kernel/gentoo-kernel-6.5.9/work/linux-6.5/fs/btrfs/scrub.c: In function ‘scrub_simple_mirror.isra’:
/var/tmp/portage/sys-kernel/gentoo-kernel-6.5.9/work/linux-6.5/fs/btrfs/scrub.c:2075:29: error: ‘found_logical’ may be used uninitialized [-Werror=maybe-uninitialized[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmaybe-uninitialized]]
  2075 |                 cur_logical = found_logical + BTRFS_STRIPE_LEN;
/var/tmp/portage/sys-kernel/gentoo-kernel-6.5.9/work/linux-6.5/fs/btrfs/scrub.c:2040:21: note: ‘found_logical’ was declared here
  2040 |                 u64 found_logical;
       |                     ^~~~~~~~~~~~~

Good find! found_logical is passed by reference to queue_scrub_stripe(..) (inlined) where it is used without ever being set:

... /* Either >0 as no more extents or <0 for error. */ if (ret) return ret; if (found_logical_ret) *found_logical_ret = stripe->logical; sctx->cur_stripe++; ...

Something is missing here, and somehow I don't think it's just the top-level initialisation of found_logical.

-h