"Jason A. Donenfeld" <Jason@xxxxxxxxx> writes: > Hi Eric, > > On Mon, Nov 28, 2022 at 7:22 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: >> >> Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx> writes: >> >> > On 19/10/2022 21:19, Jason A. Donenfeld wrote: >> >> On Wed, Oct 19, 2022 at 09:09:28PM +0100, Tvrtko Ursulin wrote: >> >>> Hm why is kthread_stop() after kthread_run() abuse? I don't see it in >> >>> kerneldoc that it must not be used for stopping threads. >> >> Because you don't want it to stop. You want to wait until it's done. If >> >> you call stop right after run, it will even stop it before it even >> >> begins to run. That's why you wind up sprinkling your msleeps >> >> everywhere, indicating that clearly this is not meant to work that way. >> > Not after kthread_run which wakes it up already. If the kerneldoc for >> > kthread_stop() is correct at least... In which case I really do think >> > that the yields are pointless/red herring. Perhaps they predate kthread_run and >> > then they were even wrong. >> > >> >>> Yep the yields and sleeps are horrible and will go. But they are also >> >>> not relevant for the topic at hand. >> >> Except they very much are. The reason you need these is because you're >> >> using kthread_stop() for something it's not meant to do. >> > >> > It is supposed to assert kthread_should_stop() which thread can look at as when >> > to exit. Except that now it can fail to get to that controlled exit >> > point. Granted that argument is moot since it implies incomplete error handling >> > in the thread anyway. >> > >> > Btw there are actually two use cases in our code base. One is thread controls >> > the exit, second is caller controls the exit. Anyway... >> > >> >>> Never mind, I was not looking for anything more than a suggestion on how >> >>> to maybe work around it in piece as someone is dealing with the affected >> >>> call sites. >> >> Sultan's kthread_work idea is probably the right direction. This would >> >> seem to have what you need. >> > >> > ... yes, it can be converted. Even though for one of the two use cases we need >> > explicit signalling. There now isn't anything which would assert >> > kthread_should_stop() without also asserting the signal, right?. Neither >> > I found that the thread work API can do it. >> > >> > Fingers crossed we were the only "abusers" of the API. There's a quite a number >> > of kthread_stop callers and it would be a large job to audit them all. >> >> >> I have been out and am coming to this late. Did this get resolved? >> >> >> I really don't expect this affected much of anything else as the code >> sat in linux-next for an entire development cycle before being merged. >> >> But I would like to make certain problems with this change were resolved. > > I just checked drm-next, and it looks like the i915 people resolved > their issue, and also got rid of those pesky yield()s in the process: > https://cgit.freedesktop.org/drm/drm/commit/?id=6407cf533217e09dfd895e64984c3f1ee3802373 > Thank you for verifying this has been resolved. Eric
