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

[Qu Wenruo <wqu@suse.de>]

On 2019/4/18 下午10:10, Josef Bacik wrote:
> On Thu, Apr 18, 2019 at 10:24:10AM +0300, Nikolay Borisov wrote:
>>
>>
>> On 18.04.19 г. 10:21 ч., Qu Wenruo wrote:
>>> There is a BUG_ON() in __clear_extent_bit() for memory allocation
>>> failure.
>>>
>>> While comment of __clear_extent_bit() says it can return error, but we
>>> always return 0.
>>>
>>> Some __clear_extent_bit() callers just ignore the return value, while
>>> some still expect error.
>>>
>>> Let's return proper error for this memory allocation anyway, to remove
>>> that BUG_ON() as a first step, so at least we can continue test.
>>
>> I remember Josef did some changes into this code and said that prealloc
>> shouldn't fail because this will cause mayhem down the road i.e. proper
>> error handling is missing. If anything I think it should be added first
>> and then remove the BUG_ONs.
> 
> I'm ok with changing this, but it needs to be more than just one patch.  Make
> alloc_extent_state_atomic() error injectable and then use either error-inject.py
> in bcc or use
> https://github.com/josefbacik/debug-scripts/blob/master/inject-error.py to test
> it and fix all the fallout from not handling lock_extent() succeeding.

Exactly what I'm going to do. With some blend from bcc inject.py, for
stack filter to provide more precious match.

> 
> You can use https://github.com/josefbacik/debug-scripts/blob/master/codepaths.py
> to find all call sites for inject-error to make sure you are catching all the
> cases.  Thanks,

That script is awesome!

Thanks,
Qu

> 
> Josef
>