On Tue, Mar 23, 2021 at 03:31:19PM +0100, Arnd Bergmann wrote:

From: Arnd Bergmann <arnd@arndb.de>

gcc complains that the ctl->max_chunk_size member might be used
uninitialized when none of the three conditions for initializing it in
init_alloc_chunk_ctl_policy_zoned() are true:

In function ‘init_alloc_chunk_ctl_policy_zoned’,
    inlined from ‘init_alloc_chunk_ctl’ at fs/btrfs/volumes.c:5023:3,
    inlined from ‘btrfs_alloc_chunk’ at fs/btrfs/volumes.c:5340:2:
include/linux/compiler-gcc.h:48:45: error: ‘ctl.max_chunk_size’ may be used uninitialized [-Werror=maybe-uninitialized]
 4998 |         ctl->max_chunk_size = min(limit, ctl->max_chunk_size);
      |                               ^~~
fs/btrfs/volumes.c: In function ‘btrfs_alloc_chunk’:
fs/btrfs/volumes.c:5316:32: note: ‘ctl’ declared here
 5316 |         struct alloc_chunk_ctl ctl;
      |                                ^~~

If we ever get into this condition, something is seriously
wrong, so the same logic as in init_alloc_chunk_ctl_policy_regular()
and a few other places should be applied. This avoids both further
data corruption, and the compile-time warning.

Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
Link: https://lore.kernel.org/lkml/20210323132343.GF7604@twin.jikos.cz/ (local)
Suggested-by: David Sterba <redacted>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Added to misc-next, thanks.