[PATCHv12 0/4] *** Detect interrupt storm in softlockup ***

[Bitao Hu]

Hi, guys.
I have implemented a low-overhead method for detecting interrupt
storm in softlockup. Please review it, all comments are welcome.

Changes from v11 to v12:

- From Douglas and Thomas, add a new kconfig knob save memory when
the softlock detector code is not enabled.

- Adjust the order of the patches; patch #1 and patch #2 are related
to genirq, while patch #3 and patch #4 are related to watchdog/softlockup,
making the dependency relationships clearer.

- Add the 'Reviewed-by' tag of Douglas.

Changes from v10 to v11:

- Only patch #2 and patch #3 have been changed.

- Add comments to explain each field of 'struct irqstat' in patch #2.

- Split the inner summation logic out of kstat_irqs() and encapsulate
it into kstat_irqs_desc() in patch #3.

- Adopt Thomas's change log for patch #3.

- Add the 'Reviewed-by' tag of Liu Song.

Changes from v9 to v10:

- The two patches related to 'watchdog/softlockup' remain unchanged.

- The majority of the work related to 'genirq' is contributed by
Thomas, indicated by adding 'Originally-by' tag. And I'd like to
express my gratitude for Thomas's contributions and guidance here.

- Adopt Thomas's change log for the snapshot mechanism for interrupt
statistics.

- Split unrelated change in patch #2 into a separate patch #3.

Changes from v8 to v9:

- Patch #1 remains unchanged.

- From Thomas Gleixner, split patch #2 into two patches. Interrupt
infrastructure first and then the actual usage site in the
watchdog code.

Changes from v7 to v8:

- From Thomas Gleixner, implement statistics within the interrupt
core code and provide sensible interfaces for the watchdog code.

- Patch #1 remains unchanged. Patch #2 has significant changes
based on Thomas's suggestions, which is why I have removed
Liu Song and Douglas's Reviewed-by from patch #2. Please review
it again, and all comments are welcome.

Changes from v6 to v7:

- Remove "READ_ONCE" in "start_counting_irqs"

- Replace the hard-coded 5 with "NUM_SAMPLE_PERIODS" macro in
"set_sample_period".

- Add empty lines to help with reading the code.

- Remove the branch that processes IRQs where "counts_diff = 0".

- Add the Reviewed-by of Liu Song and Douglas.

Changes from v5 to v6:

- Use "./scripts/checkpatch.pl --strict" to get a few extra
style nits and fix them.

- Squash patch #3 into patch #1, and wrapp the help text to
80 columns.

- Sort existing headers alphabetically in watchdog.c

- Drop "softlockup_hardirq_cpus", just read "hardirq_counts"
and see if it's non-NULL.

- Store "nr_irqs" in a local variable.

- Simplify the calculation of "cpu_diff".

Changes from v4 to v5:

- Rearranging variable placement to make code look neater.

Changes from v3 to v4:

- Renaming some variable and function names to make the code logic
more readable.

- Change the code location to avoid predeclaring.

- Just swap rather than a double loop in tabulate_irq_count.

- Since nr_irqs has the potential to grow at runtime, bounds-check
logic has been implemented.

- Add SOFTLOCKUP_DETECTOR_INTR_STORM Kconfig knob.

Changes from v2 to v3:

- From Liu Song, using enum instead of macro for cpu_stats, shortening
the name 'idx_to_stat' to 'stats', adding 'get_16bit_precesion' instead
of using right shift operations, and using 'struct irq_counts'.

- From kernel robot test, using '__this_cpu_read' and '__this_cpu_write'
instead of accessing to an per-cpu array directly, in order to avoid
this warning.
'sparse: incorrect type in initializer (different modifiers)'

Changes from v1 to v2:

- From Douglas, optimize the memory of cpustats. With the maximum number
of CPUs, that's now this.
2 * 8192 * 4 + 1 * 8192 * 5 * 4 + 1 * 8192 = 237,568 bytes.

- From Liu Song, refactor the code format and add necessary comments.

- From Douglas, use interrupt counts instead of interrupt time to
determine the cause of softlockup.

- Remove the cmdline parameter added in PATCHv1.
Bitao Hu (4):
  genirq: Provide a snapshot mechanism for interrupt statistics
  genirq: Avoid summation loops for /proc/interrupts
  watchdog/softlockup: low-overhead detection of interrupt storm
  watchdog/softlockup: report the most frequent interrupts

 arch/mips/dec/setup.c                |   2 +-
 arch/parisc/kernel/smp.c             |   2 +-
 arch/powerpc/kvm/book3s_hv_rm_xics.c |   2 +-
 include/linux/irqdesc.h              |  16 +-
 include/linux/kernel_stat.h          |   8 +
 kernel/irq/Kconfig                   |   4 +
 kernel/irq/internals.h               |   4 +-
 kernel/irq/irqdesc.c                 |  54 +++++--
 kernel/irq/proc.c                    |   9 +-
 kernel/watchdog.c                    | 213 ++++++++++++++++++++++++++-
 lib/Kconfig.debug                    |  14 ++
 scripts/gdb/linux/interrupts.py      |   6 +-
 12 files changed, 302 insertions(+), 32 deletions(-)

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