Re: [PATCH 3.18-rc3 v8 0/4] arm: Implement arch_trigger_all_cpu_backtrace

From: Daniel Thompson
Date: Mon Nov 24 2014 - 12:10:14 EST


On 14/11/14 12:35, Daniel Thompson wrote:
> Hi Thomas, Hi Jason,
>
> [Today I was *planning* to ask if patches 1 & 2 are OK for the irqchip
> tree. However just to be on the safe side I ran some build tests and
> they picked up something I overlooked last time. So instead of a poke
> I've put out a new patchset instead. Just to be sure I ran some build
> tests on the just patch 1 & 2 on their own. I couldn't find any
> mid-series build regressions so taking just the first two patches
> should present no problems.]

Are there any comments on patches 1 & 2?


Daniel.

>
> This patchset modifies the GIC driver to allow it, on supported
> platforms, to route IPI interrupts to FIQ and uses this feature to
> implement arch_trigger_all_cpu_backtrace for arm.
>
> On platforms not capable of supporting FIQ the signal to generate a
> backtrace we fall back to using IRQ for propagation instead (relying on
> a timeout to avoid wedging the CPU requesting the backtrace if other
> CPUs are not responsive).
>
> It has been tested on two systems capable of supporting grouping
> (Freescale i.MX6 and STiH416) and two that do not (vexpress-a9 and
> Qualcomm Snapdragon 600).
>
> v8:
>
> * Fixed build on arm64 causes by a spurious include file in irq-gic.c.
>
> v7-2 (accidentally released twice with same number):
>
> * Fixed boot regression on vexpress-a9 (reported by Russell King).
>
> * Rebased on v3.18-rc3; removed one patch from set that is already
> included in mainline.
>
> * Dropped arm64/fiq.h patch from the set (still useful but not related
> to issuing backtraces).
>
> v7:
>
> * Re-arranged code within the patch series to fix a regression
> introduced midway through the series and corrected by a later patch
> (testing by Olof's autobuilder). Tested offending patch in isolation
> using defconfig identified by the autobuilder.
>
> v6:
>
> * Renamed svc_entry's call_trace argument to just trace (example code
> from Russell King).
>
> * Fixed mismatched ENDPROC() in __fiq_abt (example code from Russell
> King).
>
> * Modified usr_entry to optional avoid calling into the trace code and
> used this in FIQ entry from usr path. Modified corresponding exit code
> to avoid calling into trace code and the scheduler (example code from
> Russell King).
>
> * Ensured the default FIQ register state is restored when the default
> FIQ handler is reinstalled (example code from Russell King).
>
> * Renamed no_fiq_insn to dfl_fiq_insn to reflect the effect of adopting
> a default FIQ handler.
>
> * Re-instated fiq_safe_migration_lock and associated logic in
> gic_raise_softirq(). gic_raise_softirq() is called by wake_up_klogd()
> in the console unlock logic.
>
> v5:
>
> * Rebased on 3.17-rc4.
>
> * Removed a spurious line from the final "glue it together" patch
> that broke the build.
>
> v4:
>
> * Replaced push/pop with stmfd/ldmfd respectively (review of Nicolas
> Pitre).
>
> * Really fix bad pt_regs pointer generation in __fiq_abt.
>
> * Remove fiq_safe_migration_lock and associated logic in
> gic_raise_softirq() (review of Russell King)
>
> * Restructured to introduce the default FIQ handler first, before the
> new features (review of Russell King).
>
> v3:
>
> * Removed redundant header guards from arch/arm64/include/asm/fiq.h
> (review of Catalin Marinas).
>
> * Moved svc_exit_via_fiq macro to entry-header.S (review of Nicolas
> Pitre).
>
> v2:
>
> * Restructured to sit nicely on a similar FYI patchset from Russell
> King. It now effectively replaces the work in progress final patch
> with something much more complete.
>
> * Implemented (and tested) a Thumb-2 implementation of svc_exit_via_fiq
> (review of Nicolas Pitre)
>
> * Dropped the GIC group 0 workaround patch. The issue of FIQ interrupts
> being acknowledged by the IRQ handler does still exist but should be
> harmless because the IRQ handler will still wind up calling
> ipi_cpu_backtrace().
>
> * Removed any dependency on CONFIG_FIQ; all cpu backtrace effectively
> becomes a platform feature (although the use of non-maskable
> interrupts to implement it is best effort rather than guaranteed).
>
> * Better comments highlighting usage of RAZ/WI registers (and parts of
> registers) in the GIC code.
>
> Changes *before* v1:
>
> * This patchset is a hugely cut-down successor to "[PATCH v11 00/19]
> arm: KGDB NMI/FIQ support". Thanks to Thomas Gleixner for suggesting
> the new structure. For historic details see:
> https://lkml.org/lkml/2014/9/2/227
>
> * Fix bug in __fiq_abt (no longer passes a bad struct pt_regs value).
> In fixing this we also remove the useless indirection previously
> found in the fiq_handler macro.
>
> * Make default fiq handler "always on" by migrating from fiq.c to
> traps.c and replace do_unexp_fiq with the new handler (review
> of Russell King).
>
> * Add arm64 version of fiq.h (review of Russell King)
>
> * Removed conditional branching and code from irq-gic.c, this is
> replaced by much simpler code that relies on the GIC specification's
> heavy use of read-as-zero/write-ignored (review of Russell King)
>
>
> Daniel Thompson (4):
> irqchip: gic: Make gic_raise_softirq() FIQ-safe
> irqchip: gic: Introduce plumbing for IPI FIQ
> ARM: add basic support for on-demand backtrace of other CPUs
> arm: smp: Handle ipi_cpu_backtrace() using FIQ (if available)
>
> arch/arm/include/asm/irq.h | 5 ++
> arch/arm/include/asm/smp.h | 3 +
> arch/arm/kernel/smp.c | 64 +++++++++++++++
> arch/arm/kernel/traps.c | 8 +-
> drivers/irqchip/irq-gic.c | 170 +++++++++++++++++++++++++++++++++++++---
> include/linux/irqchip/arm-gic.h | 8 ++
> 6 files changed, 245 insertions(+), 13 deletions(-)
>
> --
> 1.9.3
>

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