On Fri, Jul 1, 2022 at 5:16 PM Vincent Whitchurch <vincent.whitchurch@xxxxxxxx> wrote: > > On Fri, Jul 01, 2022 at 11:08:27AM +0200, David Gow wrote: > > On Thu, Jun 30, 2022 at 9:29 PM Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote: > > > Stack trace collection code might trigger KASAN splats when walking > > > stack frames, but this can be resolved by using unchecked accesses. > > > The main reason to disable instrumentation here is for performance > > > reasons, see the upcoming patch for arm64 [1] for some details. > > > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=802b91118d11 > > > > Ah -- that does it! Using READ_ONCE_NOCHECK() in dump_trace() gets rid > > of the nasty recursive KASAN failures we were getting in the tests. > > > > I'll send out v5 with those files instrumented again. > > Hmm, do we really want that? In the patch Andrey linked to above he > removed the READ_ONCE_NOCHECK() and added the KASAN_SANITIZE on the > corresponding files for arm64, just like it's already the case in this > patch for UML. Personally, I'm okay with the performance overhead so far: in my tests with a collection of ~350 KUnit tests, the total difference in runtime was about ~.2 seconds, and was within the margin of error caused by fluctuations in the compilation time. As an example, without the stacktrace code instrumented: [17:36:50] Testing complete. Passed: 364, Failed: 0, Crashed: 0, Skipped: 47, Errors: 0 [17:36:50] Elapsed time: 15.114s total, 0.003s configuring, 8.518s building, 6.433s running versus with it instrumented: [17:35:40] Testing complete. Passed: 364, Failed: 0, Crashed: 0, Skipped: 47, Errors: 0 [17:35:40] Elapsed time: 15.497s total, 0.003s configuring, 8.691s building, 6.640s running That being said, I'm okay with disabling it again and adding a comment if it's slow enough in some other usecase to cause problems (or even just be annoying). That could either be done in a v6 of this patchset, or a follow-up patch, depending on what people would prefer. But I'd not have a problem with leaving it instrumented for now. -- David
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