Re: 6.7.0-rc1 + hacks deadlock bug, wifi netdev delete + cat of debugfs file.

[Ben Greear <greearb@candelatech.com>]

On 11/8/23 09:39, Benjamin Berg wrote:
> On Wed, 2023-11-08 at 17:07 +0100, Johannes Berg wrote:
>>>   From the backtrace in the removal logic, it seems that something waits
>>> for a debugfs file to be closed.
>>
>> Yes, debugfs remove waits for it to no longer have active users, but
>> that cannot succeed because the users are blocked on acquiring the
>> mutex.
>>
>>> Maybe the logic attempting to get the
>>> mutex in debugfs can check if file is waiting to be deleted,
>>> combined with a try-mutex-lock logic, and bail out that way?
>>
>> I don't know if there's a way to check that, but I'm also not sure how
>> you'd even implement that?
> 
> Is it likely that we have lock contention for debugfs operations?
> 
> If it is relatively unlikely, then maybe just doing a mutex_trylock()
> and immediately failing the operation with -EAGAIN could be a solution?
> Obviously userspace would need some retry logic, but that is simple and
> it could solve the delete problem.

That is pretty nasty to expect each and every user-space app anywhere to suddenly
know that file operations are randomly unreliable...

I think we can do this where we only return no useful file data when we are actually
in teardown phase...

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com