Re: [PATCH v8 00/74] per-CPU locks

[Stefan Hajnoczi]

On Fri, Mar 27, 2020 at 11:59:37AM +0100, Philippe Mathieu-Daudé wrote:
> On 3/27/20 6:14 AM, Emilio G. Cota wrote:
> > (Apologies if I missed some Cc's; I was not Cc'ed in patch 0
> >   so I'm blindly crafting a reply.)
> > 
> > On Thu, Mar 26, 2020 at 15:30:43 -0400, Robert Foley wrote:
> > > This is a continuation of the series created by Emilio Cota.
> > > We are picking up this patch set with the goal to apply
> > > any fixes or updates needed to get this accepted.
> > 
> > Thanks for picking this up!
> > 
> > > Listed below are the changes for this version of the patch,
> > > aside from the merge related changes.
> > > 
> > > Changes for V8:
> > > - Fixed issue where in rr mode we could destroy the BQL twice.
> > 
> > I remember doing little to no testing in record-replay mode, so
> > there should be more bugs hiding in there :-)
> > 
> > > - Found/fixed bug that had been hit in testing previously during
> > > the last consideration of this patch.
> > >   We reproduced the issue hit in the qtest: bios-tables-test.
> > >   The issue was introduced by dropping the BQL, and found us
> > >   (very rarely) missing the condition variable wakeup in
> > >   qemu_tcg_rr_cpu_thread_fn().
> > 
> > Aah, this one:
> >    https://patchwork.kernel.org/patch/10838149/#22516931
> > How did you identify the problem? Was it code inspection or using a tool
> > like rr? I remember this being hard to reproduce reliably.
> > 
> > On a related note, I've done some work to get QEMU-system to work
> > under thread sanitizer, since tsan now supports our longjmp-based
> > coroutines (hurrah!). My idea was to integrate tsan in QEMU (i.e.
> > bring tsan warnings to 0) before (re)trying to merge the
> > per-CPU lock patchset; this would minimize the potential for
> > regressions, which from my personal viewpoint seems like a reasonable
> > thing to do especially now that I have little time to work on QEMU.
> > 
> > If there's interest in doing the tsan work first, then I'd be
> > happy to send to the list as soon as this weekend the changes that
> > I have so far [1].
> 
> I'm pretty sure Marc-André is interested (and also Stefan maybe), so Cc'ing
> them.

Yes, please!  tsan would be another good tool to have.

Stefan

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