Re: [PATCH for-8.0] ide: Fix manual in-flight count for TRIM BH

[Paolo Bonzini]

On 3/13/23 13:29, Fiona Ebner wrote:
> > In fact, shouldn't request queuing was enabled at the _end_ of
> > bdrv_drained_begin (once the BlockBackend has reached a quiescent
> > state on its own terms), rather than at the beginning (which leads to
> > deadlocks like this one)?
>
> Couldn't this lead to scenarios where a busy or malicious guest, which
> continues to submit new requests, slows down draining or even prevents
> it from finishing?

Possibly, but there is also a .drained_begin/.drained_end callback that 
can be defined in order to apply backpressure.  (For some other devices, 
there's also aio_disable_external/aio_enable_external that do the 
equivalent of request queuing but without the deadlocks)

Since starting the queuing of requests at the end of bdrv_drained_begin 
wouldn't hurt correctness, and it would fix this kind of deadlock, I 
think it would be worth giving it a try.

Paolo