On Wed, Sep 06, 2017 at 08:52:35AM +0900, Byungchul Park wrote: > On Tue, Sep 05, 2017 at 03:46:43PM +0200, Peter Zijlstra wrote: > > On Tue, Sep 05, 2017 at 07:58:38PM +0900, Byungchul Park wrote: > > > On Tue, Sep 05, 2017 at 07:31:44PM +0900, Byungchul Park wrote: > > > > Recursive-read and the hint I proposed(a.k.a. might) should be used for > > > > their different specific applications. Both meaning and constraints of > > > > them are totally different. > > > > > > > > Using a right function semantically is more important than making it > > > > just work, as you know. Wrong? > > > > > Of course, in the following cases, the results are same: > > > > > > recursive-read(A) -> recursive-read(A), is like nothing, and also > > > might(A) -> might(A) , is like nothing. > > > > > > recursive-read(A) -> lock(A), end in a deadlock, and also > > > might(A) -> lock(A), end in a deadlock. > > > > And these are exactly the cases we need. > > > > > Futhermore, recursive-read-might() can be used if needed, since their > > > semantics are orthogonal so they can be used in mixed forms. > > > > > > I really hope you accept the new semantics... I think current workqueue > > > code exactly needs the semantics. > > > > I really don't want to introduce this extra state if we don't have to. > > OK. If the workqueue is only user of the weird lockdep annotations, then > it might be better to defer introducing the extra state until needed. > > But, the 'might' thing I introduced would be necessary if more users > want to report deadlocks at the time for crosslocks with speculative > acquisitions like the workqueue does, since the recursive-read thing > would generate false dependencies much more than we want, while the
What do you mean by "false dependencies"? AFAICT, recursive-read could
have dependencies to the following cross commit, for example:
A(a)
ARR(a)
RRR(a)
WFC(X)
C(X)
This is a deadlock, no?
In my upcoming v2 for recursive-read support, I'm going to make this
detectable. But please note as crossrelease doesn't have any selftests
as normal lockdep stuffs, I may miss something subtle.
Regards,
Boqun
> 'might' thing generate them just as many as we want.
>
signature.asc
Description: PGP signature
