On Fri, Nov 15, 2019 at 06:14:46PM +0100, Marco Elver wrote: > On Fri, 15 Nov 2019 at 17:42, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > On Fri, Nov 15, 2019 at 01:02:08PM +0100, Marco Elver wrote: > > > On Thu, 14 Nov 2019 at 23:16, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > > > > > On Thu, Nov 14, 2019 at 10:33:03PM +0100, Marco Elver wrote: > > > > > On Thu, 14 Nov 2019, Paul E. McKenney wrote: > > > > > > > > > > > On Thu, Nov 14, 2019 at 07:02:53PM +0100, Marco Elver wrote: > > > > > > > This is the patch-series for the Kernel Concurrency Sanitizer (KCSAN). > > > > > > > KCSAN is a sampling watchpoint-based *data race detector*. More details > > > > > > > are included in **Documentation/dev-tools/kcsan.rst**. This patch-series > > > > > > > only enables KCSAN for x86, but we expect adding support for other > > > > > > > architectures is relatively straightforward (we are aware of > > > > > > > experimental ARM64 and POWER support). > > > > > > > > > > > > > > To gather early feedback, we announced KCSAN back in September, and have > > > > > > > integrated the feedback where possible: > > > > > > > http://lkml.kernel.org/r/CANpmjNPJ_bHjfLZCAPV23AXFfiPiyXXqqu72n6TgWzb2Gnu1eA@xxxxxxxxxxxxxx > > > > > > > > > > > > > > The current list of known upstream fixes for data races found by KCSAN > > > > > > > can be found here: > > > > > > > https://github.com/google/ktsan/wiki/KCSAN#upstream-fixes-of-data-races-found-by-kcsan > > > > > > > > > > > > > > We want to point out and acknowledge the work surrounding the LKMM, > > > > > > > including several articles that motivate why data races are dangerous > > > > > > > [1, 2], justifying a data race detector such as KCSAN. > > > > > > > > > > > > > > [1] https://lwn.net/Articles/793253/ > > > > > > > [2] https://lwn.net/Articles/799218/ > > > > > > > > > > > > I queued this and ran a quick rcutorture on it, which completed > > > > > > successfully with quite a few reports. > > > > > > > > > > Great. Many thanks for queuing this in -rcu. And regarding merge window > > > > > you mentioned, we're fine with your assumption to targeting the next > > > > > (v5.6) merge window. > > > > > > > > > > I've just had a look at linux-next to check what a future rebase > > > > > requires: > > > > > > > > > > - There is a change in lib/Kconfig.debug and moving KCSAN to the > > > > > "Generic Kernel Debugging Instruments" section seems appropriate. > > > > > - bitops-instrumented.h was removed and split into 3 files, and needs > > > > > re-inserting the instrumentation into the right places. > > > > > > > > > > Otherwise there are no issues. Let me know what you recommend. > > > > > > > > Sounds good! > > > > > > > > I will be rebasing onto v5.5-rc1 shortly after it comes out. My usual > > > > approach is to fix any conflicts during that rebasing operation. > > > > Does that make sense, or would you prefer to send me a rebased stack at > > > > that point? Either way is fine for me. > > > > > > That's fine with me, thanks! To avoid too much additional churn on > > > your end, I just replied to the bitops patch with a version that will > > > apply with the change to bitops-instrumented infrastructure. > > > > My first thought was to replace 8/10 of the previous version of your > > patch in -rcu (047ca266cfab "asm-generic, kcsan: Add KCSAN instrumentation > > for bitops"), but this does not apply. So I am guessing that I instead > > do this substitution when a rebase onto -rc1.. > > > > Except... > > > > > Also considering the merge window, we had a discussion and there are > > > some arguments for targeting the v5.5 merge window: > > > - we'd unblock ARM and POWER ports; > > > - we'd unblock people wanting to use the data_race macro; > > > - we'd unblock syzbot just tracking upstream; > > > Unless there are strong reasons to not target v5.5, I leave it to you > > > if you think it's appropriate. > > > > My normal process is to send the pull request shortly after -rc5 comes > > out, but you do call out some benefits of getting it in sooner, so... > > > > What I will do is to rebase your series onto (say) -rc7, test it, and > > see about an RFC pull request. > > > > One possible complication is the new 8/10 patch. But maybe it will > > apply against -rc7? > > > > Another possible complication is this: > > > > scripts/kconfig/conf --syncconfig Kconfig > > * > > * Restart config... > > * > > * > > * KCSAN: watchpoint-based dynamic data race detector > > * > > KCSAN: watchpoint-based dynamic data race detector (KCSAN) [N/y/?] (NEW) > > > > Might be OK in this case because it is quite obvious what it is doing. > > (Avoiding pain from this is the reason that CONFIG_RCU_EXPERT exists.) > > > > But I will just mention this in the pull request. > > > > If there is a -rc8, there is of course a higher probability of making it > > into the next merge window. > > > > Fair enough? > > Totally fine with that, sounds like a good plan, thanks! > > If it helps, in theory we can also drop and delay the bitops > instrumentation patch until the new bitops instrumentation > infrastructure is in 5.5-rc1. There won't be any false positives if > this is missing, we might just miss a few data races until we have it. That sounds advisable for an attempt to hit this coming merge window. So just to make sure I understand, I drop 8/10 and keep the rest during a rebase to 5.4-rc7, correct? Thanx, Paul
