watchdog/hardlockup: make HAVE_NMI_WATCHDOG sparc64-specific

There are several hardlockup detector implementations and several Kconfig
values which allow selection and build of the preferred one.

CONFIG_HARDLOCKUP_DETECTOR was introduced by the commit 23637d4
("lockup_detector: Introduce CONFIG_HARDLOCKUP_DETECTOR") in v2.6.36.
It was a preparation step for introducing the new generic perf hardlockup
detector.

The existing arch-specific variants did not support the to-be-created
generic build configurations, sysctl interface, etc. This distinction
was made explicit by the commit 4a7863c ("x86, nmi_watchdog:
Remove ARCH_HAS_NMI_WATCHDOG and rely on CONFIG_HARDLOCKUP_DETECTOR")
in v2.6.38.

CONFIG_HAVE_NMI_WATCHDOG was introduced by the commit d314d74
("nmi watchdog: do not use cpp symbol in Kconfig") in v3.4-rc1. It replaced
the above mentioned ARCH_HAS_NMI_WATCHDOG. At that time, it was still used
by three architectures, namely blackfin, mn10300, and sparc.

The support for blackfin and mn10300 architectures has been completely
dropped some time ago. And sparc is the only architecture with the historic
NMI watchdog at the moment.

And the old sparc implementation is really special. It is always built on
sparc64. It used to be always enabled until the commit 7a5c8b5
("sparc: implement watchdog_nmi_enable and watchdog_nmi_disable") added
in v4.10-rc1.

There are only few locations where the sparc64 NMI watchdog interacts
with the generic hardlockup detectors code:

  + implements arch_touch_nmi_watchdog() which is called from the generic
    touch_nmi_watchdog()

  + implements watchdog_hardlockup_enable()/disable() to support
    /proc/sys/kernel/nmi_watchdog

  + is always preferred over other generic watchdogs, see
    CONFIG_HARDLOCKUP_DETECTOR

  + includes asm/nmi.h into linux/nmi.h because some sparc-specific
    functions are needed in sparc-specific code which includes
    only linux/nmi.h.

The situation became more complicated after the commit 05a4a95
("kernel/watchdog: split up config options") and commit 2104180
("powerpc/64s: implement arch-specific hardlockup watchdog") in v4.13-rc1.
They introduced HAVE_HARDLOCKUP_DETECTOR_ARCH. It was used for powerpc
specific hardlockup detector. It was compatible with the perf one
regarding the general boot, sysctl, and programming interfaces.

HAVE_HARDLOCKUP_DETECTOR_ARCH was defined as a superset of
HAVE_NMI_WATCHDOG. It made some sense because all arch-specific
detectors had some common requirements, namely:

  + implemented arch_touch_nmi_watchdog()
  + included asm/nmi.h into linux/nmi.h
  + defined the default value for /proc/sys/kernel/nmi_watchdog

But it actually has made things pretty complicated when the generic
buddy hardlockup detector was added. Before the generic perf detector
was newer supported together with an arch-specific one. But the buddy
detector could work on any SMP system. It means that an architecture
could support both the arch-specific and buddy detector.

As a result, there are few tricky dependencies. For example,
CONFIG_HARDLOCKUP_DETECTOR depends on:

  ((HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_BUDDY) && !HAVE_NMI_WATCHDOG) || HAVE_HARDLOCKUP_DETECTOR_ARCH

The problem is that the very special sparc implementation is defined as:

  HAVE_NMI_WATCHDOG && !HAVE_HARDLOCKUP_DETECTOR_ARCH

Another problem is that the meaning of HAVE_NMI_WATCHDOG is far from clear
without reading understanding the history.

Make the logic less tricky and more self-explanatory by making
HAVE_NMI_WATCHDOG specific for the sparc64 implementation. And rename it to
HAVE_HARDLOCKUP_DETECTOR_SPARC64.

Note that HARDLOCKUP_DETECTOR_PREFER_BUDDY, HARDLOCKUP_DETECTOR_PERF,
and HARDLOCKUP_DETECTOR_BUDDY may conflict only with
HAVE_HARDLOCKUP_DETECTOR_ARCH. They depend on HARDLOCKUP_DETECTOR
and it is not longer enabled when HAVE_NMI_WATCHDOG is set.

Link: https://lkml.kernel.org/r/20230616150618.6073-5-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>

Author: pmladek

arch/Kconfig

@@ -400,33 +400,15 @@ config HAVE_HARDLOCKUP_DETECTOR_PERF
 	  The arch chooses to use the generic perf-NMI-based hardlockup
 	  detector. Must define HAVE_PERF_EVENTS_NMI.
 
-config HAVE_NMI_WATCHDOG
-	depends on HAVE_NMI
-	bool
-	help
-	  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 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
 	help

arch/sparc/Kconfig

@@ -33,7 +33,7 @@ config SPARC
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select GENERIC_PCI_IOMAP
 	select HAS_IOPORT
-	select HAVE_NMI_WATCHDOG if SPARC64
+	select HAVE_HARDLOCKUP_DETECTOR_SPARC64 if SPARC64
 	select HAVE_CBPF_JIT if SPARC32
 	select HAVE_EBPF_JIT if SPARC64
 	select HAVE_DEBUG_BUGVERBOSE

arch/sparc/Kconfig.debug

@@ -14,3 +14,12 @@ config FRAME_POINTER
 	bool
 	depends on MCOUNT
 	default y
+
+config HAVE_HARDLOCKUP_DETECTOR_SPARC64
+	depends on HAVE_NMI
+	bool
+	help
+	  Sparc64 hardlockup detector is the last one 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.

include/linux/nmi.h

@@ -9,7 +9,7 @@
 #include <asm/irq.h>
 
 /* Arch specific watchdogs might need to share extra watchdog-related APIs. */
-#if defined(CONFIG_HAVE_NMI_WATCHDOG)
+#if defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH) || defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_SPARC64)
 #include <asm/nmi.h>
 #endif
 
@@ -90,8 +90,7 @@ static inline void hardlockup_detector_disable(void) {}
 #endif
 
 /* Sparc64 has special implemetantion that is always enabled. */
-#if defined(CONFIG_HARDLOCKUP_DETECTOR) || \
-    (defined(CONFIG_HAVE_NMI_WATCHDOG) && !defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH))
+#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_SPARC64)
 void arch_touch_nmi_watchdog(void);
 #else
 static inline void arch_touch_nmi_watchdog(void) { }

kernel/watchdog.c

@@ -29,7 +29,7 @@
 
 static DEFINE_MUTEX(watchdog_mutex);
 
-#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
+#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_SPARC64)
 # define WATCHDOG_HARDLOCKUP_DEFAULT	1
 #else
 # define WATCHDOG_HARDLOCKUP_DEFAULT	0

lib/Kconfig.debug

@@ -1050,15 +1050,10 @@ config HAVE_HARDLOCKUP_DETECTOR_BUDDY
 #	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_PERF || HAVE_HARDLOCKUP_DETECTOR_BUDDY) && !HAVE_NMI_WATCHDOG) || HAVE_HARDLOCKUP_DETECTOR_ARCH
+	depends on DEBUG_KERNEL && !S390 && !HAVE_HARDLOCKUP_DETECTOR_SPARC64
+	depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_BUDDY || HAVE_HARDLOCKUP_DETECTOR_ARCH
 	imply HARDLOCKUP_DETECTOR_PERF
 	imply HARDLOCKUP_DETECTOR_BUDDY
 	select LOCKUP_DETECTOR
@@ -1079,7 +1074,7 @@ config HARDLOCKUP_DETECTOR_PREFER_BUDDY
 	bool "Prefer the buddy CPU hardlockup detector"
 	depends on HARDLOCKUP_DETECTOR
 	depends on HAVE_HARDLOCKUP_DETECTOR_PERF && HAVE_HARDLOCKUP_DETECTOR_BUDDY
-	depends on !HAVE_NMI_WATCHDOG
+	depends on !HAVE_HARLOCKUP_DETECTOR_ARCH
 	help
 	  Say Y here to prefer the buddy hardlockup detector over the perf one.
 
@@ -1095,15 +1090,15 @@ config HARDLOCKUP_DETECTOR_PERF
 	bool
 	depends on HARDLOCKUP_DETECTOR
 	depends on HAVE_HARDLOCKUP_DETECTOR_PERF && !HARDLOCKUP_DETECTOR_PREFER_BUDDY
-	depends on !HAVE_NMI_WATCHDOG
+	depends on !HAVE_HARDLOCKUP_DETECTOR_ARCH
 	select HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
 
 config HARDLOCKUP_DETECTOR_BUDDY
 	bool
 	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
+	depends on !HAVE_HARDLOCKUP_DETECTOR_ARCH
 	select HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
 
 #