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ring-buffer: add reader lock

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Impact: serialize reader accesses to individual CPU ring buffers

The code in the ring buffer expects only one reader at a time, but currently
it puts that requirement on the caller. This is not strong enough, and this
patch adds a "reader_lock" that serializes the access to the reader API
of the ring buffer.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Steven Rostedt 2008-11-11 18:47:44 +01:00 committed by Ingo Molnar
parent f536aafc5a
commit f83c9d0fe4
1 changed files with 79 additions and 32 deletions
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111
kernel/trace/ring_buffer.c
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@ -154,6 +154,7 @@ static inline int test_time_stamp(u64 delta)
struct ring_buffer_per_cpu {
int cpu;
struct ring_buffer *buffer;
spinlock_t reader_lock; /* serialize readers */
raw_spinlock_t lock;
struct lock_class_key lock_key;
struct list_head pages;
@ -321,6 +322,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
cpu_buffer->cpu = cpu;
cpu_buffer->buffer = buffer;
spin_lock_init(&cpu_buffer->reader_lock);
cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
INIT_LIST_HEAD(&cpu_buffer->pages);
@ -1476,6 +1478,9 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
/* Iterator usage is expected to have record disabled */
if (list_empty(&cpu_buffer->reader_page->list)) {
@ -1489,6 +1494,8 @@ void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
iter->read_stamp = cpu_buffer->read_stamp;
else
iter->read_stamp = iter->head_page->time_stamp;
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
/**
@ -1707,17 +1714,8 @@ static void rb_advance_iter(struct ring_buffer_iter *iter)
rb_advance_iter(iter);
}
/**
* ring_buffer_peek - peek at the next event to be read
* @buffer: The ring buffer to read
* @cpu: The cpu to peak at
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not consume the data.
*/
struct ring_buffer_event *
ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
static struct ring_buffer_event *
rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
@ -1779,16 +1777,8 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
return NULL;
}
/**
* ring_buffer_iter_peek - peek at the next event to be read
* @iter: The ring buffer iterator
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not increment the iterator.
*/
struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
static struct ring_buffer_event *
rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer *buffer;
struct ring_buffer_per_cpu *cpu_buffer;
@ -1849,6 +1839,51 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
return NULL;
}
/**
* ring_buffer_peek - peek at the next event to be read
* @buffer: The ring buffer to read
* @cpu: The cpu to peak at
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not consume the data.
*/
struct ring_buffer_event *
ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_buffer_peek(buffer, cpu, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
/**
* ring_buffer_iter_peek - peek at the next event to be read
* @iter: The ring buffer iterator
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not increment the iterator.
*/
struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
struct ring_buffer_event *event;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
/**
* ring_buffer_consume - return an event and consume it
* @buffer: The ring buffer to get the next event from
@ -1860,19 +1895,24 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
struct ring_buffer_event *
ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
unsigned long flags;
if (!cpu_isset(cpu, buffer->cpumask))
return NULL;
event = ring_buffer_peek(buffer, cpu, ts);
if (!event)
return NULL;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_buffer_peek(buffer, cpu, ts);
if (!event)
goto out;
cpu_buffer = buffer->buffers[cpu];
rb_advance_reader(cpu_buffer);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
@ -1909,11 +1949,11 @@ ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
local_irq_save(flags);
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
__raw_spin_lock(&cpu_buffer->lock);
ring_buffer_iter_reset(iter);
__raw_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return iter;
}
@ -1945,12 +1985,17 @@ struct ring_buffer_event *
ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_event *event;
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
event = ring_buffer_iter_peek(iter, ts);
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
if (!event)
return NULL;
goto out;
rb_advance_iter(iter);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
@ -1999,13 +2044,15 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
if (!cpu_isset(cpu, buffer->cpumask))
return;
local_irq_save(flags);
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
__raw_spin_lock(&cpu_buffer->lock);
rb_reset_cpu(cpu_buffer);
__raw_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
/**