diff options
| -rw-r--r-- | include/linux/perf_counter.h | 5 | ||||
| -rw-r--r-- | kernel/perf_counter.c | 130 |
2 files changed, 105 insertions, 30 deletions
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index 41aed427005..f776851f8c4 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -358,10 +358,13 @@ struct perf_mmap_data { struct rcu_head rcu_head; int nr_pages; /* nr of data pages */ - atomic_t wakeup; /* POLL_ for wakeups */ + atomic_t poll; /* POLL_ for wakeups */ atomic_t head; /* write position */ atomic_t events; /* event limit */ + atomic_t wakeup_head; /* completed head */ + atomic_t lock; /* concurrent writes */ + struct perf_counter_mmap_page *user_page; void *data_pages[0]; }; diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 75f2b6c8239..8660ae57953 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -1279,14 +1279,12 @@ static unsigned int perf_poll(struct file *file, poll_table *wait) { struct perf_counter *counter = file->private_data; struct perf_mmap_data *data; - unsigned int events; + unsigned int events = POLL_HUP; rcu_read_lock(); data = rcu_dereference(counter->data); if (data) - events = atomic_xchg(&data->wakeup, 0); - else - events = POLL_HUP; + events = atomic_xchg(&data->poll, 0); rcu_read_unlock(); poll_wait(file, &counter->waitq, wait); @@ -1568,22 +1566,6 @@ static const struct file_operations perf_fops = { void perf_counter_wakeup(struct perf_counter *counter) { - struct perf_mmap_data *data; - - rcu_read_lock(); - data = rcu_dereference(counter->data); - if (data) { - atomic_set(&data->wakeup, POLL_IN); - /* - * Ensure all data writes are issued before updating the - * user-space data head information. The matching rmb() - * will be in userspace after reading this value. - */ - smp_wmb(); - data->user_page->data_head = atomic_read(&data->head); - } - rcu_read_unlock(); - wake_up_all(&counter->waitq); if (counter->pending_kill) { @@ -1721,10 +1703,14 @@ struct perf_output_handle { int wakeup; int nmi; int overflow; + int locked; + unsigned long flags; }; -static inline void __perf_output_wakeup(struct perf_output_handle *handle) +static void perf_output_wakeup(struct perf_output_handle *handle) { + atomic_set(&handle->data->poll, POLL_IN); + if (handle->nmi) { handle->counter->pending_wakeup = 1; perf_pending_queue(&handle->counter->pending, @@ -1733,6 +1719,86 @@ static inline void __perf_output_wakeup(struct perf_output_handle *handle) perf_counter_wakeup(handle->counter); } +/* + * Curious locking construct. + * + * We need to ensure a later event doesn't publish a head when a former + * event isn't done writing. However since we need to deal with NMIs we + * cannot fully serialize things. + * + * What we do is serialize between CPUs so we only have to deal with NMI + * nesting on a single CPU. + * + * We only publish the head (and generate a wakeup) when the outer-most + * event completes. + */ +static void perf_output_lock(struct perf_output_handle *handle) +{ + struct perf_mmap_data *data = handle->data; + int cpu; + + handle->locked = 0; + + local_irq_save(handle->flags); + cpu = smp_processor_id(); + + if (in_nmi() && atomic_read(&data->lock) == cpu) + return; + + while (atomic_cmpxchg(&data->lock, 0, cpu) != 0) + cpu_relax(); + + handle->locked = 1; +} + +static void perf_output_unlock(struct perf_output_handle *handle) +{ + struct perf_mmap_data *data = handle->data; + int head, cpu; + + if (handle->wakeup) + data->wakeup_head = data->head; + + if (!handle->locked) + goto out; + +again: + /* + * The xchg implies a full barrier that ensures all writes are done + * before we publish the new head, matched by a rmb() in userspace when + * reading this position. + */ + while ((head = atomic_xchg(&data->wakeup_head, 0))) { + data->user_page->data_head = head; + handle->wakeup = 1; + } + + /* + * NMI can happen here, which means we can miss a wakeup_head update. + */ + + cpu = atomic_xchg(&data->lock, 0); + WARN_ON_ONCE(cpu != smp_processor_id()); + + /* + * Therefore we have to validate we did not indeed do so. + */ + if (unlikely(atomic_read(&data->wakeup_head))) { + /* + * Since we had it locked, we can lock it again. + */ + while (atomic_cmpxchg(&data->lock, 0, cpu) != 0) + cpu_relax(); + + goto again; + } + + if (handle->wakeup) + perf_output_wakeup(handle); +out: + local_irq_restore(handle->flags); +} + static int perf_output_begin(struct perf_output_handle *handle, struct perf_counter *counter, unsigned int size, int nmi, int overflow) @@ -1745,6 +1811,7 @@ static int perf_output_begin(struct perf_output_handle *handle, if (!data) goto out; + handle->data = data; handle->counter = counter; handle->nmi = nmi; handle->overflow = overflow; @@ -1752,12 +1819,13 @@ static int perf_output_begin(struct perf_output_handle *handle, if (!data->nr_pages) goto fail; + perf_output_lock(handle); + do { offset = head = atomic_read(&data->head); head += size; } while (atomic_cmpxchg(&data->head, offset, head) != offset); - handle->data = data; handle->offset = offset; handle->head = head; handle->wakeup = (offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT); @@ -1765,7 +1833,7 @@ static int perf_output_begin(struct perf_output_handle *handle, return 0; fail: - __perf_output_wakeup(handle); + perf_output_wakeup(handle); out: rcu_read_unlock(); @@ -1809,16 +1877,20 @@ static void perf_output_copy(struct perf_output_handle *handle, static void perf_output_end(struct perf_output_handle *handle) { - int wakeup_events = handle->counter->hw_event.wakeup_events; + struct perf_counter *counter = handle->counter; + struct perf_mmap_data *data = handle->data; + + int wakeup_events = counter->hw_event.wakeup_events; if (handle->overflow && wakeup_events) { - int events = atomic_inc_return(&handle->data->events); + int events = atomic_inc_return(&data->events); if (events >= wakeup_events) { - atomic_sub(wakeup_events, &handle->data->events); - __perf_output_wakeup(handle); + atomic_sub(wakeup_events, &data->events); + handle->wakeup = 1; } - } else if (handle->wakeup) - __perf_output_wakeup(handle); + } + + perf_output_unlock(handle); rcu_read_unlock(); } |