Am 03.08.2018 um 16:54 schrieb Andrey Grodzovsky:
[SNIP]
>
> Second of all, even after we removed the entity from rq in
> drm_sched_entity_flush to terminate any subsequent submissions
>
> to the queue the other thread doing push job can just acquire
again a
> run queue
>
> from drm_sched_entity_get_free_sched and continue submission
Hi Christian
That is actually desired.
When another process is now using the entity to submit jobs
adding it
back to the rq is actually the right thing to do cause the
entity is
still in use.
Yes, no problem if it's another process. But what about another
thread from same process ? Is it a possible use case that 2 threads
from same process submit to same entity concurrently ? If so and we
specifically kill one, the other will not stop event if we want him
to because current code makes him just require a rq for him self.
Well you can't kill a single thread of a process (you can only
interrupt it), a SIGKILL will always kill the whole process.
Is the following scenario possible and acceptable ?
2 threads from same process working on same queue where thread A
currently in drm_sched_entity_flush->wait_event_timeout (the process
getting shut down because of SIGKILL sent by user)
while thread B still inside drm_sched_entity_push_job before 'if
(reschedule)'. 'A' stopped waiting because queue became empty and then
removes the entity queue from scheduler's run queue while
B goes inside 'reschedule' because it evaluates to true ('first' is
true and all the rest of the conditions), acquires new rq, and later
adds it back to scheduler (different one maybe) and keeps submitting
jobs as much as he likes and then can be stack for up to 'timeout'
time in his drm_sched_entity_flush waiting for them.
I'm not 100% sure but I don't think that can happen.
See flushing the fd is done while dropping the fd, which happens only
after all threads of the process in question are killed.
Otherwise the flushing wouldn't make to much sense. In other words
imagine an application where a thread does a write() on a fd which is
killed.
The idea of the flush is to preserve the data and that won't work if
that isn't correctly ordered.
My understanding was that introduction of entity->last is to force
immediate termination job submissions by any thread from the
terminating process.
We could consider reordering that once more. Going to play out all
scenarios in my head over the weekend :)
Christian.
Andrey
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