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SubjectRe: task_ctx_sched_out WARN_ON triggered.
On Wed, Jan 29, 2014 at 03:07:44PM +0100, Peter Zijlstra wrote:
> Let me see if I can make a 'nice' function to dump state though, it
> might come in handy more often.

Compile tested only...

---
include/linux/perf_event.h | 4 ++
init/Kconfig | 7 ++
kernel/events/core.c | 163 ++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 173 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index e56b07f5c9b6..4921ecd019db 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -437,6 +437,10 @@ struct perf_event {
int cgrp_defer_enabled;
#endif

+#ifdef CONFIG_PERF_DEBUG
+ struct list_head debug_list;
+#endif
+
#endif /* CONFIG_PERF_EVENTS */
};

diff --git a/init/Kconfig b/init/Kconfig
index 5236dc562a36..29abe2aadb7d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1514,6 +1514,13 @@ config PERF_EVENTS

Say Y if unsure.

+config PERF_DEBUG
+ default n
+ bool "Debug: add various debug helpers and overhead"
+ depends on PERF_EVENTS && DEBUG_KERNEL
+ help
+ Say N if unsure.
+
config DEBUG_PERF_USE_VMALLOC
default n
bool "Debug: use vmalloc to back perf mmap() buffers"
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 56003c6edfd3..7d5deab0a6f0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -164,6 +164,161 @@ int sysctl_perf_event_paranoid __read_mostly = 1;
/* Minimum for 512 kiB + 1 user control page */
int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free' kiB per user */

+#ifdef CONFIG_PERF_DEBUG
+
+static char *print_event_cgroup(struct perf_event *event)
+{
+#ifdef CONFIG_CGROUP_PERF
+ static char path[PATH_MAX];
+
+ if (!event->cgrp)
+ return "(null)";
+
+ cgroup_path(event->cgrp.css.cgroup, path, PATH_MAX);
+ return path;
+#else
+ return "(null)";
+#endif
+}
+
+static char *print_task(struct task_struct *p)
+{
+ static char task[2*TASK_COMM_LEN];
+
+ if (!p)
+ return "(null)";
+
+ snprintf(task, sizeof(task), "%d/%s", p->pid, p->comm);
+ return task;
+}
+
+static char *print_event_task(struct perf_event *event)
+{
+ if (!event->ctx)
+ return "(null)";
+
+ return print_task(event->ctx->task);
+}
+
+static void print_event(struct perf_event *event)
+{
+ struct perf_event *sibling;
+
+ printk("Event (%p) created by task: %s\n", event, print_task(event->owner));
+ printk(" cpu: %d\n", event->cpu);
+ printk(" cgrp: %s\n", print_event_cgroup(event));
+ printk(" task: %s\n", print_event_task(event));
+ printk(" group: ");
+ if (event->group_leader != event) {
+ list_for_each_entry(sibling, &event->sibling_list, group_entry)
+ printk("(%p),", sibling);
+ }
+ printk("\n");
+ printk(" attr: {\n");
+
+#define Pd(_x) if (event->attr._x) printk("\t." #_x " = %lld,\n", (unsigned long long)event->attr._x)
+#define Px(_x) if (event->attr._x) printk("\t." #_x " = 0x%llx,\n", (unsigned long long)event->attr._x)
+ Pd(type);
+ Px(config);
+ if (event->attr.freq) {
+ Pd(sample_freq);
+ } else {
+ Pd(sample_period);
+ }
+ Px(sample_type);
+ Px(read_format);
+
+ Pd(disabled);
+ Pd(inherit);
+ Pd(pinned);
+ Pd(exclusive);
+ Pd(exclude_user);
+ Pd(exclude_kernel);
+ Pd(exclude_hv);
+ Pd(exclude_idle);
+ Pd(mmap);
+ Pd(comm);
+ Pd(freq);
+ Pd(inherit_stat);
+ Pd(enable_on_exec);
+ Pd(task);
+ Pd(watermark);
+ Pd(precise_ip);
+ Pd(mmap_data);
+ Pd(sample_id_all);
+ Pd(exclude_host);
+ Pd(exclude_guest);
+ Pd(exclude_callchain_kernel);
+ Pd(exclude_callchain_user);
+ Pd(mmap2);
+
+ if (event->attr.watermark) {
+ Pd(wakeup_watermark);
+ } else {
+ Pd(wakeup_events);
+ }
+ if (event->attr.type == PERF_TYPE_BREAKPOINT) {
+ Pd(bp_type);
+ Px(bp_addr);
+ Pd(bp_len);
+ } else {
+ Px(config1);
+ Px(config2);
+ }
+ Px(branch_sample_type);
+ Px(sample_regs_user);
+ Pd(sample_stack_user);
+
+ printk(" };\n");
+}
+
+static DEFINE_RAW_SPINLOCK(perf_debug_lock);
+static LIST_HEAD(perf_debug_list);
+
+static void perf_debug_print_events(void)
+{
+ struct perf_event *event;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(event, &perf_debug_list, debug_list)
+ print_event(event);
+ rcu_read_unlock();
+}
+
+static void perf_debug_add_event(struct perf_event *event)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&perf_debug_lock, flags);
+ list_add_rcu(&event->debug_list, &perf_debug_list);
+ raw_spin_unlock_irqrestore(&perf_debug_lock, flags);
+}
+
+static void perf_debug_del_event(struct perf_event *event)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&perf_debug_lock, flags);
+ list_del_rcu(&event->debug_list);
+ raw_spin_unlock_irqrestore(&perf_debug_lock, flags);
+}
+
+#else /* CONFIG_PERF_DEBUG */
+
+static inline void perf_debug_add_event(struct perf_event *event)
+{
+}
+
+static inline void perf_debug_del_event(struct perf_event *event)
+{
+}
+
+static inline void perf_debug_print_events(void)
+{
+}
+
+#endif /* CONFIG_PERF_DEBUG */
+
/*
* max perf event sample rate
*/
@@ -2377,8 +2532,10 @@ static void task_ctx_sched_out(struct perf_event_context *ctx)
if (!cpuctx->task_ctx)
return;

- if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
+ if (WARN_ON_ONCE(ctx != cpuctx->task_ctx)) {
+ perf_debug_print_events();
return;
+ }

ctx_sched_out(ctx, cpuctx, EVENT_ALL);
cpuctx->task_ctx = NULL;
@@ -3227,6 +3384,7 @@ static void __free_event(struct perf_event *event)
if (event->ctx)
put_ctx(event->ctx);

+ perf_debug_del_event(event);
call_rcu(&event->rcu_head, free_event_rcu);
}
static void free_event(struct perf_event *event)
@@ -6764,6 +6922,8 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
}
}

+ perf_debug_add_event(event);
+
return event;

err_pmu:

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