On Sat, Nov 16, 2019 at 07:09:21PM +0100, Marco Elver wrote: > On Sat, 16 Nov 2019 at 16:34, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > On Sat, Nov 16, 2019 at 09:20:54AM +0100, Marco Elver wrote: > > > On Fri, 15 Nov 2019 at 21:43, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > > > > > 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? > > > > > > Yes, that's right. > > > > Very good, I just now pushed a "kcsan" branch on -rcu, and am running > > rcutorture, first without KCSAN enabled and then with it turned on. > > If all that works out, I set my -next branch to that point and see what > > -next testing and kbuild test robot think about it. If all goes well, > > an RFC pull request. > > > > Look OK? > > Looks good to me, many thanks! And I did get one failure on the KCSAN=n run for the TREE03 scenario, but it does not appear to be your fault. Looks like a race between a swait_queue_head swake_up_one() invocation and one of the CPU hotplug operations done late in system shutdown. I have included the splat below for your amusement. Starting the KCSAN=y runs now. Thanx, Paul ------------------------------------------------------------------------ [ 601.009355] reboot: Power down [ 601.010447] ------------[ cut here ]------------ [ 601.011020] sched: Unexpected reschedule of offline CPU#1! [ 601.011639] WARNING: CPU: 7 PID: 0 at arch/x86/kernel/apic/ipi.c:67 native_smp_send_reschedule+0x2f/0x40 [ 601.012692] Modules linked in: [ 601.013037] CPU: 7 PID: 0 Comm: swapper/7 Not tainted 5.4.0-rc7+ #1497 [ 601.013755] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1ubuntu1 04/01/2014 [ 601.014708] RIP: 0010:native_smp_send_reschedule+0x2f/0x40 [ 601.015312] Code: 05 f6 62 5d 01 73 15 48 8b 05 cd ba 28 01 be fd 00 00 00 48 8b 40 30 e9 bf b0 db 00 89 fe 48 c7 c7 d0 df 5e a7 e8 01 20 02 00 <0f> 0b c3 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 48 8b 05 99 ba [ 601.017357] RSP: 0018:ffffa1afc020cee0 EFLAGS: 00010086 [ 601.017942] RAX: 0000000000000000 RBX: ffff8d5c1ed24a54 RCX: 0000000000000005 [ 601.018716] RDX: 0000000080000005 RSI: 0000000000000082 RDI: 00000000ffffffff [ 601.019500] RBP: 0000000000000000 R08: 0000000000000cd5 R09: 000000000000003d [ 601.020283] R10: ffff8d5c1f067f80 R11: 20666f20656c7564 R12: 0000000000000001 [ 601.021074] R13: 0000000000027f40 R14: 0000000000000087 R15: ffff8d5c1ed23f00 [ 601.021851] FS: 0000000000000000(0000) GS:ffff8d5c1f1c0000(0000) knlGS:0000000000000000 [ 601.022731] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 601.023360] CR2: 00000000ffffffff CR3: 000000001120a000 CR4: 00000000000006e0 [ 601.024140] Call Trace: [ 601.024437] <IRQ> [ 601.024671] try_to_wake_up+0x2b3/0x650 [ 601.025103] swake_up_locked.part.6+0xe/0x30 [ 601.025579] swake_up_one+0x22/0x30 [ 601.025968] rcu_try_advance_all_cbs+0x71/0x80 [ 601.026459] rcu_cleanup_after_idle+0x28/0x40 [ 601.026941] rcu_irq_enter+0xfb/0x130 [ 601.027347] irq_enter+0x5/0x50 [ 601.027704] smp_reboot_interrupt+0x1a/0xb0 [ 601.028175] ? smp_apic_timer_interrupt+0xa1/0x180 [ 601.028711] reboot_interrupt+0xf/0x20 [ 601.029134] </IRQ> [ 601.029374] RIP: 0010:default_idle+0x1e/0x170 [ 601.029853] Code: 90 90 90 90 90 90 90 90 90 90 90 90 41 55 41 54 55 53 e8 c5 c5 91 ff 0f 1f 44 00 00 e9 07 00 00 00 0f 00 2d e6 b4 54 00 fb f4 <e8> ad c5 91 ff 89 c5 0f 1f 44 00 00 5b 5d 41 5c 41 5d c3 65 8b 05 [ 601.031884] RSP: 0018:ffffa1afc00afec0 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff07 [ 601.032716] RAX: 0000000000000007 RBX: 0000000000000007 RCX: 0000000000000007 [ 601.033498] RDX: 0000000000000001 RSI: 0000000000000087 RDI: ffffffffa769a760 [ 601.034280] RBP: ffffffffa7a1c160 R08: 0000009a8e03a656 R09: 0000000000000001 [ 601.035062] R10: 0000000000000400 R11: 00000000000001d8 R12: 0000000000000000 [ 601.035842] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 601.036632] do_idle+0x1a6/0x240 [ 601.036996] cpu_startup_entry+0x14/0x20 [ 601.037433] start_secondary+0x150/0x180 [ 601.037869] secondary_startup_64+0xa4/0xb0 [ 601.038339] ---[ end trace e4c21199f3882c03 ]--- [ 601.038991] acpi_power_off called
