On Sat, Mar 5, 2022, 4:47 AM Jin-oh Kang jinoh.kang.kr@gmail.com wrote:
On Sat, Mar 5, 2022, 4:05 AM Jinoh Kang jinoh.kang.kr@gmail.com wrote:
On 3/5/22 02:47, Zebediah Figura wrote:
Right, but I think it's possible to trigger this assert now. For a
rather pathological case, consider a client which calls set_async_direct_result on an async which is currently being serviced by a device driver and has not yet reached get_next_device_request.
For that to be possible, something has to terminate the async so that set_async_direct_result does not reject it. The easiest way to do so is to cancel it, or make it timeout somehow.
In fact, I think we have discovered an _existing_ bug: the client can use set_async_direct_result to interfere with cancelled asyncs (device-backed or not).
Further investigation revealed some other bugs, which is tangentially related:
- An async may time out before the client calls set_async_direct_result
to report back the status of initial I/O. In this case, the timeout is ignored. 2. There is a time window where alerted asyncs ignore IoCancel/IoCancelEx requests. If async_terminate( async, STATUS_ALERTED ) is called, the async will ignore any cancellation requests until the APC_ASYNC_IO routine returns. Note that this bug has existed *before* set_async_direct_result, and I think this one may need to be addressed first.
So what I think we need here is a mechanism to tell alerted asyncs apart from irreversibly-terminated asyncs.
To make it clear, it should be "restartable" vs. "non-restartable" asyncs. See below...
This will solve all of the problems above:
- It's no longer possible to call set_async_direct_result on a device
async in the first place, since it will now reject irreversibly-terminated asyncs while still accepting alerted asyncs (which is not possible for device asyncs).
Actually it's possible for devive asyncs to be in alerted state, but note that it is *not* supposed to be restartable.
On the second thought, the output copy APC call gets fake STATUS_ALERTED, so I think it doesn't apply here.
- Timeout and cancellation works as expected: set_async_direct_result will
treat timed out asyncs as irreversibly-terminated. (the client needs to be modified to handle this case explicitly, though.)
Any thoughts?
(And as mentioned, we should probably be calling
async_set_initial_status() in async_set_result, in which case this could be triggered much less pathologically by the controlling process dying.)
That has been split off as patch 2/8.
-- Sincerely, Jinoh Kang