linux/kernel/rcu/Kconfig.debug

# SPDX-License-Identifier: GPL-2.0-only
#
# RCU-related debugging configuration options
#

menu "RCU Debugging"

config PROVE_RCU
	def_bool PROVE_LOCKING

config PROVE_RCU_LIST
	bool "RCU list lockdep debugging"
	depends on PROVE_RCU && RCU_EXPERT
	default n
	help
	  Enable RCU lockdep checking for list usages. By default it is
	  turned off since there are several list RCU users that still
	  need to be converted to pass a lockdep expression. To prevent
	  false-positive splats, we keep it default disabled but once all
	  users are converted, we can remove this config option.

config TORTURE_TEST
	tristate
	default n

config RCU_SCALE_TEST
	tristate "performance tests for RCU"
	depends on DEBUG_KERNEL
	select TORTURE_TEST
	default n
	help
	  This option provides a kernel module that runs performance
	  tests on the RCU infrastructure.  The kernel module may be built
	  after the fact on the running kernel to be tested, if desired.

	  Say Y here if you want RCU performance tests to be built into
	  the kernel.
	  Say M if you want the RCU performance tests to build as a module.
	  Say N if you are unsure.

config RCU_TORTURE_TEST
	tristate "torture tests for RCU"
	depends on DEBUG_KERNEL
	select TORTURE_TEST
	default n
	help
	  This option provides a kernel module that runs torture tests
	  on the RCU infrastructure.  The kernel module may be built
	  after the fact on the running kernel to be tested, if desired.

	  Say Y here if you want RCU torture tests to be built into
	  the kernel.
	  Say M if you want the RCU torture tests to build as a module.
	  Say N if you are unsure.

config RCU_TORTURE_TEST_CHK_RDR_STATE
	bool "Check rcutorture reader state"
	depends on RCU_TORTURE_TEST
	default n
	help
	  This option causes rcutorture to check the desired rcutorture
	  reader state for each segment against the actual context.
	  Note that PREEMPT_COUNT must be enabled if the preempt-disabled
	  and bh-disabled checks are to take effect, and that PREEMPT_RCU
	  must be enabled for the RCU-nesting checks to take effect.
	  These checks add overhead, and this Kconfig options is therefore
	  disabled by default.

	  Say Y here if you want rcutorture reader contexts checked.
	  Say N if you are unsure.

config RCU_TORTURE_TEST_LOG_CPU
	bool "Log CPU for rcutorture failures"
	depends on RCU_TORTURE_TEST
	default n
	help
	  This option causes rcutorture to decorate each entry of its
	  log of failure/close-call rcutorture reader segments with the
	  number of the CPU that the reader was running on at the time.
	  This information can be useful, but it does incur additional
	  overhead, overhead that can make both failures and close calls
	  less probable.

	  Say Y here if you want CPU IDs logged.
	  Say N if you are unsure.

config RCU_TORTURE_TEST_LOG_GP
	bool "Log grace-period numbers for rcutorture failures"
	depends on RCU_TORTURE_TEST
	default n
	help
	  This option causes rcutorture to decorate each entry of its
	  log of failure/close-call rcutorture reader segments with the
	  corresponding grace-period sequence numbers.	This information
	  can be useful, but it does incur additional overhead, overhead
	  that can make both failures and close calls less probable.

	  Say Y here if you want grace-period sequence numbers logged.
	  Say N if you are unsure.

config RCU_REF_SCALE_TEST
	tristate "Scalability tests for read-side synchronization (RCU and others)"
	depends on DEBUG_KERNEL
	select TORTURE_TEST
	default n
	help
	  This option provides a kernel module that runs performance tests
	  useful comparing RCU with various read-side synchronization mechanisms.
	  The kernel module may be built after the fact on the running kernel to be
	  tested, if desired.

	  Say Y here if you want these performance tests built into the kernel.
	  Say M if you want to build it as a module instead.
	  Say N if you are unsure.

config RCU_CPU_STALL_TIMEOUT
	int "RCU CPU stall timeout in seconds"
	depends on RCU_STALL_COMMON
	range 3 300
	default 21
	help
	  If a given RCU grace period extends more than the specified
	  number of seconds, a CPU stall warning is printed.  If the
	  RCU grace period persists, additional CPU stall warnings are
	  printed at more widely spaced intervals.

config RCU_EXP_CPU_STALL_TIMEOUT
	int "Expedited RCU CPU stall timeout in milliseconds"
	depends on RCU_STALL_COMMON
	range 0 300000
	default 0
	help
	  If a given expedited RCU grace period extends more than the
	  specified number of milliseconds, a CPU stall warning is printed.
	  If the RCU grace period persists, additional CPU stall warnings
	  are printed at more widely spaced intervals.  A value of zero
	  says to use the RCU_CPU_STALL_TIMEOUT value converted from
	  seconds to milliseconds.

config RCU_CPU_STALL_CPUTIME
	bool "Provide additional RCU stall debug information"
	depends on RCU_STALL_COMMON
	default n
	help
	  Collect statistics during the sampling period, such as the number of
	  (hard interrupts, soft interrupts, task switches) and the cputime of
	  (hard interrupts, soft interrupts, kernel tasks) are added to the
	  RCU stall report. For multiple continuous RCU stalls, all sampling
	  periods begin at half of the first RCU stall timeout.
	  The boot option rcupdate.rcu_cpu_stall_cputime has the same function
	  as this one, but will override this if it exists.

config RCU_CPU_STALL_NOTIFIER
	bool "Provide RCU CPU-stall notifiers"
	depends on RCU_STALL_COMMON
	depends on DEBUG_KERNEL
	depends on RCU_EXPERT
	default n
	help
	  WARNING:  You almost certainly do not want this!!!

	  Enable RCU CPU-stall notifiers, which are invoked just before
	  printing the RCU CPU stall warning.  As such, bugs in notifier
	  callbacks can prevent stall warnings from being printed.
	  And the whole reason that a stall warning is being printed is
	  that something is hung up somewhere.	Therefore, the notifier
	  callbacks must be written extremely carefully, preferably
	  containing only lockless code.  After all, it is quite possible
	  that the whole reason that the RCU CPU stall is happening in
	  the first place is that someone forgot to release whatever lock
	  that you are thinking of acquiring.  In which case, having your
	  notifier callback acquire that lock will hang, preventing the
	  RCU CPU stall warning from appearing.

	  Say Y here if you want RCU CPU stall notifiers (you don't want them)
	  Say N if you are unsure.

config RCU_TRACE
	bool "Enable tracing for RCU"
	depends on DEBUG_KERNEL
	default y if TREE_RCU
	select TRACE_CLOCK
	help
	  This option enables additional tracepoints for ftrace-style
	  event tracing.

	  Say Y here if you want to enable RCU tracing
	  Say N if you are unsure.

config RCU_EQS_DEBUG
	bool "Provide debugging asserts for adding NO_HZ support to an arch"
	depends on DEBUG_KERNEL
	help
	  This option provides consistency checks in RCU's handling of
	  NO_HZ.  These checks have proven quite helpful in detecting
	  bugs in arch-specific NO_HZ code.

	  Say N here if you need ultimate kernel/user switch latencies
	  Say Y if you are unsure

config RCU_STRICT_GRACE_PERIOD
	bool "Provide debug RCU implementation with short grace periods"
	depends on DEBUG_KERNEL && RCU_EXPERT && NR_CPUS <= 4 && !TINY_RCU
	default n
	select PREEMPT_COUNT if PREEMPT=n
	help
	  Select this option to build an RCU variant that is strict about
	  grace periods, making them as short as it can.  This limits
	  scalability, destroys real-time response, degrades battery
	  lifetime and kills performance.  Don't try this on large
	  machines, as in systems with more than about 10 or 20 CPUs.
	  But in conjunction with tools like KASAN, it can be helpful
	  when looking for certain types of RCU usage bugs, for example,
	  too-short RCU read-side critical sections.

endmenu # "RCU Debugging"