btrfs: reduce stack usage for btrfsic_process_written_block

btrfs: reduce stack usage for btrfsic_process_written_block

btrfsic_process_written_block() cals btrfsic_process_metablock(),
which has a fairly large stack usage due to the btrfsic_stack_frame
variable. It also calls btrfsic_test_for_metadata(), which now
needs several hundreds of bytes for its SHASH_DESC_ON_STACK().

In some configurations, we end up with both functions on the
same stack, and gcc warns about the excessive stack usage that
might cause the available stack space to run out:

fs/btrfs/check-integrity.c:1743:13: error: stack frame size of 1152 bytes in function 'btrfsic_process_written_block' [-Werror,-Wframe-larger-than=]

Marking both child functions as noinline_for_stack helps because
this guarantees that the large variables are not on the same
stack frame.

Fixes: d5178578bcd4 ("btrfs: directly call into crypto framework for checksumming")
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David Sterba <dsterba@suse.com>