Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull v5.10 RCU changes from Paul E. McKenney:

- Debugging for smp_call_function().

- Strict grace periods for KASAN.  The point of this series is to find
  RCU-usage bugs, so the corresponding new RCU_STRICT_GRACE_PERIOD
  Kconfig option depends on both DEBUG_KERNEL and RCU_EXPERT, and is
  further disabled by dfefault.  Finally, the help text includes
  a goodly list of scary caveats.

- New smp_call_function() torture test.

- Torture-test updates.

- Documentation updates.

- Miscellaneous fixes.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

lib/Kconfig.debug

@@ -1367,6 +1367,27 @@ config WW_MUTEX_SELFTEST
 	  Say M if you want these self tests to build as a module.
 	  Say N if you are unsure.
 
+config SCF_TORTURE_TEST
+	tristate "torture tests for smp_call_function*()"
+	depends on DEBUG_KERNEL
+	select TORTURE_TEST
+	help
+	  This option provides a kernel module that runs torture tests
+	  on the smp_call_function() family of primitives.  The kernel
+	  module may be built after the fact on the running kernel to
+	  be tested, if desired.
+
+config CSD_LOCK_WAIT_DEBUG
+	bool "Debugging for csd_lock_wait(), called from smp_call_function*()"
+	depends on DEBUG_KERNEL
+	depends on 64BIT
+	default n
+	help
+	  This option enables debug prints when CPUs are slow to respond
+	  to the smp_call_function*() IPI wrappers.  These debug prints
+	  include the IPI handler function currently executing (if any)
+	  and relevant stack traces.
+
 endmenu # lock debugging
 
 config TRACE_IRQFLAGS

lib/nmi_backtrace.c

@@ -85,12 +85,16 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
 	put_cpu();
 }
 
+// Dump stacks even for idle CPUs.
+static bool backtrace_idle;
+module_param(backtrace_idle, bool, 0644);
+
 bool nmi_cpu_backtrace(struct pt_regs *regs)
 {
 	int cpu = smp_processor_id();
 
 	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
-		if (regs && cpu_in_idle(instruction_pointer(regs))) {
+		if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
 			pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
 				cpu, (void *)instruction_pointer(regs));
 		} else {