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ring-buffer: Use sync sched protection on ring buffer resizing

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There was a comment in the ring buffer code that says the calling
layers should prevent tracing or reading of the ring buffer while
resizing. I have discovered that the tracers do not honor this
arrangement.

This patch moves the disabling and synchronizing the ring buffer to
a higher layer during resizing. This guarantees that no writes
are occurring while the resize takes place.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2009-12-10 22:54:27 -05:00 committed by Steven Rostedt
parent d954fbf0ff
commit 184210154b
1 changed files with 9 additions and 16 deletions
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25
kernel/trace/ring_buffer.c
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@ -1193,9 +1193,6 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
struct list_head *p;
unsigned i;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
spin_lock_irq(&cpu_buffer->reader_lock);
rb_head_page_deactivate(cpu_buffer);
@ -1214,9 +1211,6 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
spin_unlock_irq(&cpu_buffer->reader_lock);
rb_check_pages(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
}
static void
@ -1227,9 +1221,6 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
struct list_head *p;
unsigned i;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
spin_lock_irq(&cpu_buffer->reader_lock);
rb_head_page_deactivate(cpu_buffer);
@ -1245,8 +1236,6 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
spin_unlock_irq(&cpu_buffer->reader_lock);
rb_check_pages(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
}
/**
@ -1254,11 +1243,6 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
* @buffer: the buffer to resize.
* @size: the new size.
*
* The tracer is responsible for making sure that the buffer is
* not being used while changing the size.
* Note: We may be able to change the above requirement by using
* RCU synchronizations.
*
* Minimum size is 2 * BUF_PAGE_SIZE.
*
* Returns -1 on failure.
@ -1290,6 +1274,11 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
if (size == buffer_size)
return size;
atomic_inc(&buffer->record_disabled);
/* Make sure all writers are done with this buffer. */
synchronize_sched();
mutex_lock(&buffer->mutex);
get_online_cpus();
@ -1352,6 +1341,8 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
put_online_cpus();
mutex_unlock(&buffer->mutex);
atomic_dec(&buffer->record_disabled);
return size;
free_pages:
@ -1361,6 +1352,7 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
}
put_online_cpus();
mutex_unlock(&buffer->mutex);
atomic_dec(&buffer->record_disabled);
return -ENOMEM;
/*
@ -1370,6 +1362,7 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
out_fail:
put_online_cpus();
mutex_unlock(&buffer->mutex);
atomic_dec(&buffer->record_disabled);
return -1;
}
EXPORT_SYMBOL_GPL(ring_buffer_resize);