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? Thanx, Paul
