[PATCHv8 0/2] *** 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 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 (2):
  watchdog/softlockup: low-overhead detection of interrupt
  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              |   9 +-
 include/linux/kernel_stat.h          |   4 +
 kernel/irq/internals.h               |   2 +-
 kernel/irq/irqdesc.c                 |  34 ++++-
 kernel/irq/proc.c                    |   9 +-
 kernel/watchdog.c                    | 213 ++++++++++++++++++++++++++-
 lib/Kconfig.debug                    |  13 ++
 scripts/gdb/linux/interrupts.py      |   6 +-
 11 files changed, 269 insertions(+), 27 deletions(-)

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