| Message ID | 20230906160505.2431857-1-dianders@chromium.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | arm64: Add IPI for backtraces / kgdb; try to use NMI for some IPIs | expand |
On Wed, 06 Sep 2023 09:02:55 -0700, Douglas Anderson wrote: > This is an attempt to resurrect Sumit's old patch series [1] that > allowed us to use the arm64 pseudo-NMI to get backtraces of CPUs and > also to round up CPUs in kdb/kgdb. The last post from Sumit that I > could find was v7, so I started my series at v8. I haven't copied all > of his old changelongs here, but you can find them from the link. > > This patch series targets v6.6. Specifically it can't land in v6.5 > since it depends on commit 8d539b84f1e3 ("nmi_backtrace: allow > excluding an arbitrary CPU"). > > [...] Applied to arm64 (for-next/backtrace-ipi), thanks! [1/7] irqchip/gic-v3: Enable support for SGIs to act as NMIs https://git.kernel.org/arm64/c/a02026bf9da1 [2/7] arm64: idle: Tag the arm64 idle functions as __cpuidle https://git.kernel.org/arm64/c/d0c14a7d36f0 [3/7] arm64: smp: Remove dedicated wakeup IPI https://git.kernel.org/arm64/c/2b2d0a7a96ab [4/7] arm64: smp: Add arch support for backtrace using pseudo-NMI https://git.kernel.org/arm64/c/331a1b3a836c [5/7] arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI https://git.kernel.org/arm64/c/d7402513c935 [6/7] arm64: kgdb: Implement kgdb_roundup_cpus() to enable pseudo-NMI roundup https://git.kernel.org/arm64/c/2f5cd0c7ffde [7/7] arm64: smp: Mark IPI globals as __ro_after_init https://git.kernel.org/arm64/c/62817d5ba25d
This is an attempt to resurrect Sumit's old patch series [1] that allowed us to use the arm64 pseudo-NMI to get backtraces of CPUs and also to round up CPUs in kdb/kgdb. The last post from Sumit that I could find was v7, so I started my series at v8. I haven't copied all of his old changelongs here, but you can find them from the link. This patch series targets v6.6. Specifically it can't land in v6.5 since it depends on commit 8d539b84f1e3 ("nmi_backtrace: allow excluding an arbitrary CPU"). It should be noted that Mark still feels there might be some corner cases where pseudo-NMI is not production ready [2] [3], but as far as I'm aware there are no concrete/documented issues. Regardless of whether this should be enabled for production, though, this series will be invaluable to anyone trying to debug crashes on arm64 machines. v13 of this series fixes a nit with the names of two functions and collects more tags. There are no code changes other than the renames and these have no functional impact. I believe that the series is ready to land. As per the note in patch #1, I'm hoping for an Ack from Marc Zyngier on patch #1 and then the whole series can land through the arm64 tree. v12 of this series collects tags, fixes a few small nits in comments and commit messages from v11 and adds a new (and somewhat unrelated) small patch to the end of the series. There are no code changes other than the last patch, which is tiny. v11 of this series addressed Stephen Boyd's feedback on v10 and added a missing "static" that the patches robot found. v10 of this series attempted to address all of Mark's feedback on v9. As a quick summary: - It includes his patch to remove IPI_WAKEUP, freeing up an extra IPI. - It no longer combines the "kgdb" and "backtrace" IPIs. If we need another IPI these could always be recombined later. - It promotes IPI_CPU_STOP and IPI_CPU_CRASH_STOP to NMI. - It puts nearly all the code directly in smp.c. - Several of the patches are squashed together. - Patch #6 ("kgdb: Provide a stub kgdb_nmicallback() if !CONFIG_KGDB") was dropped from the series since it landed. Between v8 and v9, I had cleaned up this patch series by integrating the 10th patch from v8 [4] into the whole series. As part of this, I renamed the "NMI IPI" to the "debug IPI" since it could now be backed by a regular IPI in the case that pseudo NMIs weren't available. With the fallback, this allowed me to drop some extra patches from the series. This feels (to me) to be pretty clean and hopefully others agree. Any patch I touched significantly I removed Masayoshi and Chen-Yu's tags from. ...also in v8, I reorderd the patches a bit in a way that seemed a little cleaner to me. Since v7, I have: * Addressed the small amount of feedback that was there for v7. * Rebased. * Added a new patch that prevents us from spamming the logs with idle tasks. * Added an extra patch to gracefully fall back to regular IPIs if pseudo-NMIs aren't there. It can be noted that this patch series works very well with the recent "hardlockup" patches that have landed through Andrew Morton's tree and are currently in mainline. It works especially well with the "buddy" lockup detector. [1] https://lore.kernel.org/linux-arm-kernel/1604317487-14543-1-git-send-email-sumit.garg@linaro.org/ [2] https://lore.kernel.org/lkml/ZFvGqD%2F%2Fpm%2FlZb+p@FVFF77S0Q05N.cambridge.arm.com/ [3] https://lore.kernel.org/lkml/ZNDKVP2m-iiZCz3v@FVFF77S0Q05N.cambridge.arm.com [4] https://lore.kernel.org/r/20230419155341.v8.10.Ic3659997d6243139d0522fc3afcdfd88d7a5f030@changeid/ Changes in v13: - s/_idx/_index/ on the patch to make function names consistent. Changes in v12: - ("arm64: smp: Mark IPI globals as __ro_after_init") new for v12. - Added a comment about why we account for 16 SGIs when Linux uses 8. - Minor comment change to add "()" after nmi_trigger_cpumask_backtrace. - Updated the commit hash of the commit this depends on. Changes in v11: - Adjust comment about NR_IPI/MAX_IPI. - Don't use confusing "backed by" idiom in comment. - Made arm64_backtrace_ipi() static. - Updated commit message as per Stephen. - arch_send_wakeup_ipi() now takes an unsigned int. Changes in v10: - ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for v10. - ("arm64: smp: Remove dedicated wakeup IPI") new for v10. - Backtrace now directly supported in smp.c - Don't allocate the cpumask on the stack; just iterate. - Moved kgdb calls to smp.c to avoid needing to export IPI info. - Rewrite as needed for 5.11+ as per Mark Rutland and Sumit. - Squash backtrace into patch adding support for pseudo-NMI IPIs. - kgdb now has its own IPI. Changes in v9: - Added comments that we might not be using NMI always. - Added to commit message that this doesn't catch all cases. - Fold in v8 patch #10 ("Fallback to a regular IPI if NMI isn't enabled") - Moved header file out of "include" since it didn't need to be there. - Remove arm64_supports_nmi() - Remove fallback for when debug IPI isn't available. - Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI. - arch_trigger_cpumask_backtrace() no longer returns bool Changes in v8: - "Tag the arm64 idle functions as __cpuidle" new for v8 - Removed "#ifdef CONFIG_SMP" since arm64 is always SMP - debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param Douglas Anderson (6): irqchip/gic-v3: Enable support for SGIs to act as NMIs arm64: idle: Tag the arm64 idle functions as __cpuidle arm64: smp: Add arch support for backtrace using pseudo-NMI arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI arm64: kgdb: Implement kgdb_roundup_cpus() to enable pseudo-NMI roundup arm64: smp: Mark IPI globals as __ro_after_init Mark Rutland (1): arm64: smp: Remove dedicated wakeup IPI arch/arm64/include/asm/irq.h | 3 + arch/arm64/include/asm/smp.h | 4 +- arch/arm64/kernel/acpi_parking_protocol.c | 2 +- arch/arm64/kernel/idle.c | 4 +- arch/arm64/kernel/smp.c | 139 +++++++++++++++++----- drivers/irqchip/irq-gic-v3.c | 59 ++++++--- 6 files changed, 160 insertions(+), 51 deletions(-)