__link_block_group uses GFP_KERNEL

[Denis Kirjanov]

Hi guys,

Looks like that current code does GFP_KERNEL allocation inside
__link_block_group.
the function invokes kobject_add and internally creates sysfs files
with the GFP_KERNEL flag set.
But since do_chunk_alloc executes insides the btrfs transaction it's
not allowed to sleep.

Thanks!