Am 23.06.2022 um 13:19 hat Emanuele Giuseppe Esposito geschrieben: > > > Am 23/06/2022 um 13:10 schrieb Vladimir Sementsov-Ogievskiy: > > On 6/23/22 12:08, Emanuele Giuseppe Esposito wrote: > >> > >> > >> Am 22/06/2022 um 20:38 schrieb Vladimir Sementsov-Ogievskiy: > >>> On 6/22/22 17:26, Emanuele Giuseppe Esposito wrote: > >>>> > >>>> > >>>> Am 21/06/2022 um 19:26 schrieb Vladimir Sementsov-Ogievskiy: > >>>>> On 6/16/22 16:18, Emanuele Giuseppe Esposito wrote: > >>>>>> With the*nop* job_lock/unlock placed, rename the static > >>>>>> functions that are always under job_mutex, adding "_locked" suffix. > >>>>>> > >>>>>> List of functions that get this suffix: > >>>>>> job_txn_ref job_txn_del_job > >>>>>> job_txn_apply job_state_transition > >>>>>> job_should_pause job_event_cancelled > >>>>>> job_event_completed job_event_pending > >>>>>> job_event_ready job_event_idle > >>>>>> job_do_yield job_timer_not_pending > >>>>>> job_do_dismiss job_conclude > >>>>>> job_update_rc job_commit > >>>>>> job_abort job_clean > >>>>>> job_finalize_single job_cancel_async > >>>>>> job_completed_txn_abort job_prepare > >>>>>> job_needs_finalize job_do_finalize > >>>>>> job_transition_to_pending job_completed_txn_success > >>>>>> job_completed job_cancel_err > >>>>>> job_force_cancel_err > >>>>>> > >>>>>> Note that "locked" refers to the*nop* job_lock/unlock, and not > >>>>>> real_job_lock/unlock. > >>>>>> > >>>>>> No functional change intended. > >>>>>> > >>>>>> Signed-off-by: Emanuele Giuseppe Esposito<eespo...@redhat.com> > >>>>> > >>>>> > >>>>> Hmm. Maybe it was already discussed.. But for me it seems, that it > >>>>> would > >>>>> be simpler to review previous patches, that fix job_ API users to use > >>>>> locking properly, if this renaming go earlier. > >>>>> > >>>>> Anyway, in this series, we can't update everything at once. So > >>>>> patch to > >>>>> patch, we make the code more and more correct. (yes I remember that > >>>>> lock() is a noop, but I should review thinking that it real, > >>>>> otherwise, > >>>>> how to review?) > >>>>> > >>>>> So, I'm saying about formal correctness of using lock() unlock() > >>>>> function in connection with introduced _locked prifixes and in > >>>>> connection with how it should finally work. > >>>>> > >>>>> You do: > >>>>> > >>>>> 05. introduce some _locked functions, that just duplicates, and > >>>>> job_pause_point_locked() is formally inconsistent, as I said. > >>>>> > >>>>> 06. Update a lot of places, to give them their final form (but not > >>>>> final, as some functions will be renamed to _locked, some not, hard to > >>>>> imagine) > >>>>> > >>>>> 07,08,09. Update some more, and even more places. very hard to track > >>>>> formal correctness of using locks > >>>>> > >>>>> 10-...: rename APIs. > >>>>> > >>>>> > >>>>> What do you think about the following: > >>>>> > >>>>> 1. Introduce noop lock, and some internal _locked() versions, and keep > >>>>> formal consistency inside job.c, considering all public interfaces as > >>>>> unlocked: > >>>>> > >>>>> at this point: > >>>>> - everything correct inside job.c > >>>>> - no public interfaces with _locked prefix > >>>>> - all public interfaces take mutex internally > >>>>> - no external user take mutex by hand > >>>>> > >>>>> We can rename all internal static functions at this step too. > >>>>> > >>>>> 2. Introduce some public _locked APIs, that we'll use in next patches > >>>>> > >>>>> 3. Now start fixing external users in several patches: > >>>>> - protect by mutex direct use of job fields > >>>>> - make wider locks and move to _locked APIs inside them where > >>>>> needed > >>>>> > >>>>> > >>>>> In this scenario, every updated unit becomes formally correct after > >>>>> update, and after all steps everything is formally correct, and we can > >>>>> move to turning-on the mutex. > >>>>> > >>>> > >>>> I don't understand your logic also here, sorry :( > >>>> > >>>> I assume you want to keep patch 1-4, then the problem is assing > >>>> job_lock > >>>> and renaming functions in _locked. > >>>> So I would say the problem is in patch 5-6-10-11-12-13. All the others > >>>> should be self contained. > >>>> > >>>> I understand patch 5 is a little hard to follow. > >>>> > >>>> Now, I am not sure what you propose here but it seems that the end goal > >>>> is to just have the same result, but with additional intermediate steps > >>>> that are just "do this just because in the next patch will be useful". > >>>> I think the problem is that we are going to miss the "why we need the > >>>> lock" logic in the patches if we do so. > >>>> > >>>> The logic I tried to convey in this order is the following: > >>>> - job.h: add _locked duplicates for job API functions called with and > >>>> without job_mutex > >>>> Just create duplicates of functions > >>>> > >>>> - jobs: protect jobs with job_lock/unlock > >>>> QMP and monitor functions call APIs that assume lock is taken, > >>>> drivers must take explicitly the lock > >>>> > >>>> - jobs: rename static functions called with job_mutex held > >>>> - job.h: rename job API functions called with job_mutex held > >>>> - block_job: rename block_job functions called with job_mutex held > >>>> *given* that some functions are always under lock, transform > >>>> them in _locked. Requires the job_lock/unlock patch > >>>> > >>>> - job.h: define unlocked functions > >>>> Comments on the public functions that are not _locked > >>>> > >>>> > >>>> @Kevin, since you also had some feedbacks on the patch ordering, do you > >>>> agree with this ordering or you have some other ideas? > >>>> > >>>> Following your suggestion, we could move patches 10-11-12-13 before > >>>> patch 6 "jobs: protect jobs with job_lock/unlock". > >>>> > >>>> (Apologies for changing my mind, but being the second complain I am > >>>> starting to reconsider reordering the patches). > >>>> > >>> > >>> In two words, what I mean: let's keep the following invariant from patch > >>> to patch: > >>> > >>> 1. Function that has _locked() prefix is always called with lock held > >>> 2. Function that has _locked() prefix never calls functions that take > >>> lock by themselves so that would dead-lock > >>> 3. Function that is documented as "called with lock not held" is never > >>> called with lock held > >>> > >>> That what I mean by "formal correctness": yes, we know that lock is > >>> noop, but still let's keep code logic to correspond function naming and > >>> comments that we add. > >>> > >> > >> Ok I get what you mean, but then we have useless changes for public > >> functions that eventually will only be _locked() like job_next_locked: > >> > >> The function is always called in a loop, so it is pointless to take the > >> lock inside. Therefore the patch would be "incorrect" on its own anyways. > >> > >> Then, we would have a patch where we add the lock guard inside, and > >> another one where we remove it and rename to _locked and take the lock > >> outside. Seems unnecessary to me. > > > > For me it looks a bit simpler than you describe. And anyway keeping the > > correctness from patch to patch worth the complexity. I'll give an > > argument. > > > > First what is the best practices? Best practices is when every patch is > > good and absolutely correct. So that you can apply any number of patches > > from the beginning of the series (01-NN), commit them to master and this > > will break neither compilation, nor tests, nor readability, nothing. > > This makes the review process iterable: if I'm OK with patches 01-03, I > > give them r-b and don't think about them. I don't have to keep in mind > > any tricky things. And I can review 04 several days later not rereading > > 01-03 (or at least I can consider applied 01-03 as a good correct base > > state). This way I'm sure, that if I reviewed all patches one-by-one, > > each one is correct, then the whole thing is correct. > > > > A lot harder to review when we have only collective correctness: the > > whole series being applied make a correct thing, but we can't say it > > about intermediate states. In your series we can't be absolutely correct > > with each patch, as we have to switch from aio-context lock to mutex in > > one patch, that's why mutex is added as noop. That's a reasonable and > > (seems) unsolvable drawback. That's a thing I have to keep in mind > > during the whole review. But I'd prefer not add more such things, like > > comments and _locked suffixes that don't correspond to the code. > > > > With the invariant that I propose, the following logic works: > > > > If > > 1. we keep the invariant from patch to patch > > AND > > 2. at the end we have updated all users of the internal and external > > APIs, not missed some file or function > > Then everything is correct at the end. > > > > Without the invariant I can't prove that everything is correct at the > > end, as it is hard to follow the degree of correctness from patch to > > patch. In your way the only invariant that we have from patch to patch, > > is that mutex is noop, so all changes do nothing, and therefore they are > > correct. This way I can give an r-b to all such patches not thinking > > about details, they are noop. But when I finally have to review the > > patch that turns on the mutex, I'll have to recheck all internal and > > external API users, which is equivalent to review all the changes merged > > into one patch. > > > > > > > > Consider the case with job_next. The most correct way to update it IMHO: > > > > 1. Add lock inside job_next() and add job_next_locked() - in one patch > > with other similar changes of job.c and job.h. > > > > At this moment we have job_next() calls in a loop, which is not good (we > > want larger critical section), but that doesn't break the invariant I > > proposed above. > > The only thing I am pointing here is that this breaks "readability", > meaning if someone bisects here it will find a very weird situation > (aside from the fact that there is a noop lock). > > But I guess this is fine, as long as I write it in the commit message. > > And since these patch are waiting here for more than 3 months now, I > would say if the others (Kevin?) agree I will change the order with what > you proposed here.
Yes, I think Vladimir is having the same difficulties with reading the series as I had. And I believe his suggestion would make the intermediate states less impossible to review. The question is how much work it would be and whether you're willing to do this. As I said, if reorganising is too hard, I'm okay with just ignoring the intermediate state and reviewing the series as if it were a single patch. Kevin
