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kernel/smp: Provide CSD lock timeout diagnostics

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This commit causes csd_lock_wait() to emit diagnostics when a CPU
fails to respond quickly enough to one of the smp_call_function()
family of function calls.  These diagnostics are enabled by a new
CSD_LOCK_WAIT_DEBUG Kconfig option that depends on DEBUG_KERNEL.

This commit was inspired by an earlier patch by Josef Bacik.

[ paulmck: Fix for syzbot+0f719294463916a3fc0e@syzkaller.appspotmail.com ]
[ paulmck: Fix KASAN use-after-free issue reported by Qian Cai. ]
[ paulmck: Fix botched nr_cpu_ids comparison per Dan Carpenter. ]
[ paulmck: Apply Peter Zijlstra feedback. ]
Link: https://lore.kernel.org/lkml/00000000000042f21905a991ecea@google.com
Link: https://lore.kernel.org/lkml/0000000000002ef21705a9933cf3@google.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-06-30 13:22:54 -07:00
parent e48c15b796
commit 35feb60474
2 changed files with 141 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

132
kernel/smp.c
View file

@ -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)
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);
}
@ -375,7 +501,8 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
csd->func = func;
csd->info = info;
#ifdef CONFIG_64BIT
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
csd->src = smp_processor_id();
csd->dst = cpu;
#endif
@ -543,7 +670,8 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
csd->flags |= CSD_TYPE_SYNC;
csd->func = func;
csd->info = info;
#ifdef CONFIG_64BIT
#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)))

11
lib/Kconfig.debug
View file

@ -1367,6 +1367,17 @@ config WW_MUTEX_SELFTEST
Say M if you want these self tests to build as a module.
Say N if you are unsure.
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