Re: [PATCH v4 1/3] btrfs: add might_sleep() to some places in update_qgroup_limit_item()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/11/16 16:09, ChenXiaoSong wrote:
> 在 2022/11/16 6:48, Qu Wenruo 写道:
>> Looks good.
>>
>> We may want to add more in other locations, but this is really a good 
>> start.
>>
>> Reviewed-by: Qu Wenruo <wqu@suse.com>
>>
>> Thanks,
>> Qu
> 
> If I just add might_sleep() in btrfs_alloc_path() and 
> btrfs_search_slot(), is it reasonable?

Adding it to btrfs_search_slot() is definitely correct.

But why for btrfs_alloc_path()? Wouldn't kmem_cache_zalloc() itself 
already do the might_sleep_if() somewhere?

I just looked the call chain, and indeed it is doing the check already:

btrfs_alloc_path()
|- kmem_cache_zalloc()
    |- kmem_cache_alloc()
       |- __kmem_cache_alloc_lru()
          |- slab_alloc()
             |- slab_alloc_node()
                |- slab_pre_alloc_hook()
                   |- might_alloc()
                      |- might_sleep_if()

Thanks,
Qu

> 
> Or just add might_sleep() to one place in update_qgroup_limit_item() ?