Re: [PATCH 1/1] io_uring: use proper references for fallback_req locking

[Jens Axboe <axboe@kernel.dk>]

On 5/3/20 6:52 AM, Pavel Begunkov wrote:
> On 30/04/2020 17:52, Jens Axboe wrote:
>> On 4/29/20 6:47 PM, Bijan Mottahedeh wrote:
>>> Use ctx->fallback_req address for test_and_set_bit_lock() and
>>> clear_bit_unlock().
>>
>> Thanks, applied.
>>
> 
> How about getting rid of it? As once was fairly noticed, we're screwed in many
> other ways in case of OOM. Otherwise we at least need to make async context
> allocation more resilient.

Not sure how best to handle it, it really sucks to have things fall apart
under high memory pressure, a condition that isn't that rare in production
systems. But as you say, it's only a half measure currently. We could have
the fallback request have req->io already allocated, though. That would
provide what we need for guaranteed forward progress, even in the presence
of OOM conditions.

-- 
Jens Axboe