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watchdog/hardlockup: make the config checks more straightforward

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There are four possible variants of hardlockup detectors:

  + buddy: available when SMP is set.

  + perf: available when HAVE_HARDLOCKUP_DETECTOR_PERF is set.

  + arch-specific: available when HAVE_HARDLOCKUP_DETECTOR_ARCH is set.

  + sparc64 special variant: available when HAVE_NMI_WATCHDOG is set
	and HAVE_HARDLOCKUP_DETECTOR_ARCH is not set.

The check for the sparc64 variant is more complicated because
HAVE_NMI_WATCHDOG is used to #ifdef code used by both arch-specific
and sparc64 specific variant. Therefore it is automatically
selected with HAVE_HARDLOCKUP_DETECTOR_ARCH.

This complexity is partly hidden in HAVE_HARDLOCKUP_DETECTOR_NON_ARCH.
It reduces the size of some checks but it makes them harder to follow.

Finally, the other temporary variable HARDLOCKUP_DETECTOR_NON_ARCH
is used to re-compute HARDLOCKUP_DETECTOR_PERF/BUDDY when the global
HARDLOCKUP_DETECTOR switch is enabled/disabled.

Make the logic more straightforward by the following changes:

  + Better explain the role of HAVE_HARDLOCKUP_DETECTOR_ARCH and
    HAVE_NMI_WATCHDOG in comments.

  + Add HAVE_HARDLOCKUP_DETECTOR_BUDDY so that there is separate
    HAVE_* for all four hardlockup detector variants.

    Use it in the other conditions instead of SMP. It makes it
    clear that it is about the buddy detector.

  + Open code HAVE_HARDLOCKUP_DETECTOR_NON_ARCH in HARDLOCKUP_DETECTOR
    and HARDLOCKUP_DETECTOR_PREFER_BUDDY. It helps to understand
    the conditions between the four hardlockup detector variants.

  + Define the exact conditions when HARDLOCKUP_DETECTOR_PERF/BUDDY
    can be enabled. It explains the dependency on the other
    hardlockup detector variants.

    Also it allows to remove HARDLOCKUP_DETECTOR_NON_ARCH by using "imply".
    It triggers re-evaluating HARDLOCKUP_DETECTOR_PERF/BUDDY when
    the global HARDLOCKUP_DETECTOR switch is changed.

  + Add dependency on HARDLOCKUP_DETECTOR so that the affected variables
    disappear when the hardlockup detectors are disabled.

    Another nice side effect is that HARDLOCKUP_DETECTOR_PREFER_BUDDY
    value is not preserved when the global switch is disabled.
    The user has to make the decision again when it gets re-enabled.

Link: https://lkml.kernel.org/r/20230616150618.6073-3-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Petr Mladek 2023-06-16 17:06:14 +02:00 committed by Andrew Morton
parent 4917a25f83
commit 1356d0b966
2 changed files with 53 additions and 32 deletions
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23
arch/Kconfig
View File

@ -404,17 +404,28 @@ config HAVE_NMI_WATCHDOG
depends on HAVE_NMI
bool
help
The arch provides a low level NMI watchdog. It provides
asm/nmi.h, and defines its own watchdog_hardlockup_probe() and
arch_touch_nmi_watchdog().
The arch provides its own hardlockup detector implementation instead
of the generic ones.
Sparc64 defines this variable without HAVE_HARDLOCKUP_DETECTOR_ARCH.
It is the last arch-specific implementation which was developed before
adding the common infrastructure for handling hardlockup detectors.
It is always built. It does _not_ use the common command line
parameters and sysctl interface, except for
/proc/sys/kernel/nmi_watchdog.
config HAVE_HARDLOCKUP_DETECTOR_ARCH
bool
select HAVE_NMI_WATCHDOG
help
The arch chooses to provide its own hardlockup detector, which is
a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
interfaces and parameters provided by hardlockup detector subsystem.
The arch provides its own hardlockup detector implementation instead
of the generic ones.
It uses the same command line parameters, and sysctl interface,
as the generic hardlockup detectors.
HAVE_NMI_WATCHDOG is selected to build the code shared with
the sparc64 specific implementation.
config HAVE_PERF_REGS
bool

62
lib/Kconfig.debug
View File

@ -1035,16 +1035,33 @@ config BOOTPARAM_SOFTLOCKUP_PANIC
Say N if unsure.
config HAVE_HARDLOCKUP_DETECTOR_BUDDY
bool
depends on SMP
default y
#
# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard
# lockup detector rather than the perf based detector.
# Global switch whether to build a hardlockup detector at all. It is available
# only when the architecture supports at least one implementation. There are
# two exceptions. The hardlockup detector is never enabled on:
#
# s390: it reported many false positives there
#
# sparc64: has a custom implementation which is not using the common
# hardlockup command line options and sysctl interface.
#
# Note that HAVE_NMI_WATCHDOG is used to distinguish the sparc64 specific
# implementaion. It is automatically enabled also for other arch-specific
# variants which set HAVE_HARDLOCKUP_DETECTOR_ARCH. It makes the check
# of avaialable and supported variants quite tricky.
#
config HARDLOCKUP_DETECTOR
bool "Detect Hard Lockups"
depends on DEBUG_KERNEL && !S390
depends on HAVE_HARDLOCKUP_DETECTOR_NON_ARCH || HAVE_HARDLOCKUP_DETECTOR_ARCH
depends on ((HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_BUDDY) && !HAVE_NMI_WATCHDOG) || HAVE_HARDLOCKUP_DETECTOR_ARCH
imply HARDLOCKUP_DETECTOR_PERF
imply HARDLOCKUP_DETECTOR_BUDDY
select LOCKUP_DETECTOR
select HARDLOCKUP_DETECTOR_NON_ARCH if HAVE_HARDLOCKUP_DETECTOR_NON_ARCH
help
Say Y here to enable the kernel to act as a watchdog to detect
@ -1055,9 +1072,14 @@ config HARDLOCKUP_DETECTOR
chance to run. The current stack trace is displayed upon detection
and the system will stay locked up.
#
# Note that arch-specific variants are always preferred.
#
config HARDLOCKUP_DETECTOR_PREFER_BUDDY
bool "Prefer the buddy CPU hardlockup detector"
depends on HAVE_HARDLOCKUP_DETECTOR_PERF && SMP
depends on HARDLOCKUP_DETECTOR
depends on HAVE_HARDLOCKUP_DETECTOR_PERF && HAVE_HARDLOCKUP_DETECTOR_BUDDY
depends on !HAVE_NMI_WATCHDOG
help
Say Y here to prefer the buddy hardlockup detector over the perf one.
@ -1071,39 +1093,27 @@ config HARDLOCKUP_DETECTOR_PREFER_BUDDY
config HARDLOCKUP_DETECTOR_PERF
bool
depends on HAVE_HARDLOCKUP_DETECTOR_PERF
depends on HARDLOCKUP_DETECTOR
depends on HAVE_HARDLOCKUP_DETECTOR_PERF && !HARDLOCKUP_DETECTOR_PREFER_BUDDY
depends on !HAVE_NMI_WATCHDOG
select HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
config HARDLOCKUP_DETECTOR_BUDDY
bool
depends on SMP
depends on HARDLOCKUP_DETECTOR
depends on HAVE_HARDLOCKUP_DETECTOR_BUDDY
depends on !HAVE_HARDLOCKUP_DETECTOR_PERF || HARDLOCKUP_DETECTOR_PREFER_BUDDY
depends on !HAVE_NMI_WATCHDOG
select HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
#
# Both the "perf" and "buddy" hardlockup detectors count hrtimer
# interrupts. This config enables functions managing this common code.
#
config HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
bool
select SOFTLOCKUP_DETECTOR
# For hardlockup detectors you can have one directly provided by the arch
# or use a "non-arch" one. If you're using a "non-arch" one that is
# further divided the perf hardlockup detector (which, confusingly, needs
# arch-provided perf support) and the buddy hardlockup detector (which just
# needs SMP). In either case, using the "non-arch" code conflicts with
# the NMI watchdog code (which is sometimes used directly and sometimes used
# by the arch-provided hardlockup detector).
config HAVE_HARDLOCKUP_DETECTOR_NON_ARCH
bool
depends on (HAVE_HARDLOCKUP_DETECTOR_PERF || SMP) && !HAVE_NMI_WATCHDOG
default y
# This will select the appropriate non-arch hardlockdup detector
config HARDLOCKUP_DETECTOR_NON_ARCH
bool
depends on HAVE_HARDLOCKUP_DETECTOR_NON_ARCH
select HARDLOCKUP_DETECTOR_BUDDY if !HAVE_HARDLOCKUP_DETECTOR_PERF || HARDLOCKUP_DETECTOR_PREFER_BUDDY
select HARDLOCKUP_DETECTOR_PERF if HAVE_HARDLOCKUP_DETECTOR_PERF && !HARDLOCKUP_DETECTOR_PREFER_BUDDY
#
# Enables a timestamp based low pass filter to compensate for perf based
# hard lockup detection which runs too fast due to turbo modes.