Commit 6fe208f6 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

Merge branch 'csd.2020.09.04a' into HEAD 

csd.2020.09.04a: CPU smp_call_function() torture tests.
parents 7fbe67e4 2b722160

Documentation/admin-guide/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -3073,6 +3073,10 @@ 
			and gids from such clients.  This is intended to ease

			migration from NFSv2/v3.



	nmi_backtrace.backtrace_idle [KNL]

			Dump stacks even of idle CPUs in response to an

			NMI stack-backtrace request.



	nmi_debug=	[KNL,SH] Specify one or more actions to take

			when a NMI is triggered.

			Format: [state][,regs][,debounce][,die]

include/linux/smp.h

+3 −0
Original line number Diff line number Diff line
@@ -26,6 +26,9 @@ struct __call_single_data { 
		struct {

			struct llist_node llist;

			unsigned int flags;

#ifdef CONFIG_64BIT

			u16 src, dst;

#endif

		};

	};

	smp_call_func_t func;

include/linux/smp_types.h

+3 −0
Original line number Diff line number Diff line
@@ -61,6 +61,9 @@ struct __call_single_node { 
		unsigned int	u_flags;

		atomic_t	a_flags;

	};

#ifdef CONFIG_64BIT

	u16 src, dst;

#endif

};



#endif /* __LINUX_SMP_TYPES_H */

kernel/smp.c

+134 −0
Original line number Diff line number Diff line
@@ -20,6 +20,9 @@ 
#include <linux/sched.h>

#include <linux/sched/idle.h>

#include <linux/hypervisor.h>

#include <linux/sched/clock.h>

#include <linux/nmi.h>

#include <linux/sched/debug.h>



#include "smpboot.h"

#include "sched/smp.h"
@@ -96,6 +99,103 @@ void __init call_function_init(void) 
	smpcfd_prepare_cpu(smp_processor_id());

}



#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG



static DEFINE_PER_CPU(call_single_data_t *, cur_csd);

static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);

static DEFINE_PER_CPU(void *, cur_csd_info);



#define CSD_LOCK_TIMEOUT (5ULL * NSEC_PER_SEC)

static atomic_t csd_bug_count = ATOMIC_INIT(0);



/* Record current CSD work for current CPU, NULL to erase. */

static void csd_lock_record(call_single_data_t *csd)

{

	if (!csd) {

		smp_mb(); /* NULL cur_csd after unlock. */

		__this_cpu_write(cur_csd, NULL);

		return;

	}

	__this_cpu_write(cur_csd_func, csd->func);

	__this_cpu_write(cur_csd_info, csd->info);

	smp_wmb(); /* func and info before csd. */

	__this_cpu_write(cur_csd, csd);

	smp_mb(); /* Update cur_csd before function call. */

		  /* Or before unlock, as the case may be. */

}



static __always_inline int csd_lock_wait_getcpu(call_single_data_t *csd)

{

	unsigned int csd_type;



	csd_type = CSD_TYPE(csd);

	if (csd_type == CSD_TYPE_ASYNC || csd_type == CSD_TYPE_SYNC)

		return csd->dst; /* Other CSD_TYPE_ values might not have ->dst. */

	return -1;

}



/*

 * Complain if too much time spent waiting.  Note that only

 * the CSD_TYPE_SYNC/ASYNC types provide the destination CPU,

 * so waiting on other types gets much less information.

 */

static __always_inline bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, int *bug_id)

{

	int cpu = -1;

	int cpux;

	bool firsttime;

	u64 ts2, ts_delta;

	call_single_data_t *cpu_cur_csd;

	unsigned int flags = READ_ONCE(csd->flags);



	if (!(flags & CSD_FLAG_LOCK)) {

		if (!unlikely(*bug_id))

			return true;

		cpu = csd_lock_wait_getcpu(csd);

		pr_alert("csd: CSD lock (#%d) got unstuck on CPU#%02d, CPU#%02d released the lock.\n",

			 *bug_id, raw_smp_processor_id(), cpu);

		return true;

	}



	ts2 = sched_clock();

	ts_delta = ts2 - *ts1;

	if (likely(ts_delta <= CSD_LOCK_TIMEOUT))

		return false;



	firsttime = !*bug_id;

	if (firsttime)

		*bug_id = atomic_inc_return(&csd_bug_count);

	cpu = csd_lock_wait_getcpu(csd);

	if (WARN_ONCE(cpu < 0 || cpu >= nr_cpu_ids, "%s: cpu = %d\n", __func__, cpu))

		cpux = 0;

	else

		cpux = cpu;

	cpu_cur_csd = smp_load_acquire(&per_cpu(cur_csd, cpux)); /* Before func and info. */

	pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %llu ns for CPU#%02d %pS(%ps).\n",

		 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts2 - ts0,

		 cpu, csd->func, csd->info);

	if (cpu_cur_csd && csd != cpu_cur_csd) {

		pr_alert("\tcsd: CSD lock (#%d) handling prior %pS(%ps) request.\n",

			 *bug_id, READ_ONCE(per_cpu(cur_csd_func, cpux)),

			 READ_ONCE(per_cpu(cur_csd_info, cpux)));

	} else {

		pr_alert("\tcsd: CSD lock (#%d) %s.\n",

			 *bug_id, !cpu_cur_csd ? "unresponsive" : "handling this request");

	}

	if (cpu >= 0) {

		if (!trigger_single_cpu_backtrace(cpu))

			dump_cpu_task(cpu);

		if (!cpu_cur_csd) {

			pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n", *bug_id, raw_smp_processor_id(), cpu);

			arch_send_call_function_single_ipi(cpu);

		}

	}

	dump_stack();

	*ts1 = ts2;



	return false;

}



/*

 * csd_lock/csd_unlock used to serialize access to per-cpu csd resources

 *
@@ -103,10 +203,30 @@ void __init call_function_init(void) 
 * previous function call. For multi-cpu calls its even more interesting

 * as we'll have to ensure no other cpu is observing our csd.

 */

static __always_inline void csd_lock_wait(call_single_data_t *csd)

{

	int bug_id = 0;

	u64 ts0, ts1;



	ts1 = ts0 = sched_clock();

	for (;;) {

		if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id))

			break;

		cpu_relax();

	}

	smp_acquire__after_ctrl_dep();

}



#else

static void csd_lock_record(call_single_data_t *csd)

{

}



static __always_inline void csd_lock_wait(call_single_data_t *csd)

{

	smp_cond_load_acquire(&csd->flags, !(VAL & CSD_FLAG_LOCK));

}

#endif



static __always_inline void csd_lock(call_single_data_t *csd)

{
@@ -166,9 +286,11 @@ static int generic_exec_single(int cpu, call_single_data_t *csd) 
		 * We can unlock early even for the synchronous on-stack case,

		 * since we're doing this from the same CPU..

		 */

		csd_lock_record(csd);

		csd_unlock(csd);

		local_irq_save(flags);

		func(info);

		csd_lock_record(NULL);

		local_irq_restore(flags);

		return 0;

	}
@@ -268,8 +390,10 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline) 
				entry = &csd_next->llist;

			}



			csd_lock_record(csd);

			func(info);

			csd_unlock(csd);

			csd_lock_record(NULL);

		} else {

			prev = &csd->llist;

		}
@@ -296,8 +420,10 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline) 
				smp_call_func_t func = csd->func;

				void *info = csd->info;



				csd_lock_record(csd);

				csd_unlock(csd);

				func(info);

				csd_lock_record(NULL);

			} else if (type == CSD_TYPE_IRQ_WORK) {

				irq_work_single(csd);

			}
@@ -375,6 +501,10 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info, 


	csd->func = func;

	csd->info = info;

#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG

	csd->src = smp_processor_id();

	csd->dst = cpu;

#endif



	err = generic_exec_single(cpu, csd);
@@ -540,6 +670,10 @@ static void smp_call_function_many_cond(const struct cpumask *mask, 
			csd->flags |= CSD_TYPE_SYNC;

		csd->func = func;

		csd->info = info;

#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG

		csd->src = smp_processor_id();

		csd->dst = cpu;

#endif

		if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))

			__cpumask_set_cpu(cpu, cfd->cpumask_ipi);

	}

lib/Kconfig.debug

+11 −0
Original line number Diff line number Diff line
@@ -1377,6 +1377,17 @@ config SCF_TORTURE_TEST 
	  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