Re: [PATCH] btrfs: extent_io: Handle memory allocation failure in __clear_extent_bit()

[Nikolay Borisov <nborisov@suse.com>]

On 18.04.19 г. 14:54 ч., Qu Wenruo wrote:
<snip>

> 
> Forgot to mention, for that method, I'll definitely keep the BUG_ON() on
> @prealloc.
> 
> Just make the allocation part fall back to use fs_info->last_chance[] to
> grab a valid memory slot.

Before you go and re-invent the wheel I will suggest you take a look at
the mempool api (include/linux/mempool.h). AFAIK it's purpose is to
exactly ensure memory allocations from it will not fail (depending on
how the pool is configured)

> 
> Thanks,
> Qu
> 
>>
>> The main reason I'm doing such error injection test is to ensure write
>> time tree checker is not the cause of the lockup.
>>
>> Of course I can directly inject error into btrfs_check_leaf_full() and
>> btrfs_check_node(), and filter the stack to ensure it only happen in
>> write time, and that's already what I'm crafting, based on the bcc error
>> inject example and kprobe return value overriding.
>>
>> But it will never be a bad idea to explore what can go wrong.
>> And "always BUG_ON()" -> "good enough (TM)" already looks like a
>> improvement to me.
>>
>> Thanks,
>> Qu
>>
>