On Fri, Dec 12, 2025 at 11:15:29AM +0100, Marco Elver wrote: > On Fri, 12 Dec 2025 at 10:43, Peter Zijlstra <[email protected]> wrote: > [..] > > > Correct. We're trading false negatives over false positives at this > > > point, just to get things to compile cleanly. > > > > Right, and this all 'works' right up to the point someone sticks a > > must_not_hold somewhere. > > > > > > > Better support for Linux's scoped guard design could be added in > > > > > future if deemed critical. > > > > > > > > I would think so, per the above I don't think this is 'right'. > > > > > > It's not sound, but we'll avoid false positives for the time being. > > > Maybe we can wrangle the jigsaw of macros to let it correctly acquire > > > and then release (via a 2nd cleanup function), it might be as simple > > > as marking the 'constructor' with the right __acquires(..), and then > > > have a 2nd __attribute__((cleanup)) variable that just does a no-op > > > release via __release(..) so we get the already supported pattern > > > above. > > > > Right, like I mentioned in my previous email; it would be lovely if at > > the very least __always_inline would get a *very* early pass such that > > the above could be resolved without inter-procedural bits. I really > > don't consider an __always_inline as another procedure. > > > > Because as I already noted yesterday, cleanup is now all > > __always_inline, and as such *should* all end up in the one function. > > > > But yes, if we can get a magical mash-up of __cleanup and __release (let > > it be knows as __release_on_cleanup ?) that might also work I suppose. > > But I vastly prefer __always_inline actually 'working' ;-) > > The truth is that __always_inline working in this way is currently > infeasible. Clang and LLVM's architecture simply disallow this today: > the semantic analysis that -Wthread-safety does happens over the AST, > whereas always_inline is processed by early passes in the middle-end > already within LLVM's pipeline, well after semantic analysis. There's > a complexity budget limit for semantic analysis (type checking, > warnings, assorted other errors), and path-sensitive & > intra-procedural analysis over the plain AST is outside that budget. > Which is why tools like clang-analyzer exist (symbolic execution), > where it's possible to afford that complexity since that's not > something that runs for a normal compile. > > I think I've pushed the current version of Clang's -Wthread-safety > already far beyond what folks were thinking is possible (a variant of > alias analysis), but even my healthy disregard for the impossible > tells me that making path-sensitive intra-procedural analysis even if > just for __always_inline functions is quite possibly a fool's errand.
Well, I had to propose it. Gotta push the envelope :-) > So either we get it to work with what we have, or give up. So I think as is, we can start. But I really do want the cleanup thing sorted, even if just with that __release_on_cleanup mashup or so.
