Qu Wenruo <wqu@xxxxxxxx> writes: > On 2023/10/27 00:30, Holger Hoffstätte wrote: >> 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. > > This looks like a false alert for me. > > @found_logical is intentionally uninitialized to catch any > uninitialized usage by compiler. > I feel like this sort of thing is going to be inevitable with -Wmaybe-uninitialized. > It would be set by queue_scrub_stripe() when there is any stripe found. > > If there is no stripe found, queue_scrub_stripe() would return >0, > then we know there is no more extent and break the loop. > If there is any error, we error out too, thus no problem with that. > > So to me this looks like a false alert. > > Mind to share the compiler and its version? > Sure, GCC 14.0.0 20231022 (experimental). Sorry, I'd meant to include that in the original post.. > Thanks, > Qu >> -h
