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Subject[PATCH 1/2] [PATCH 1/2] ring-buffer: Use sync sched protection on ring buffer resizing
From: Steven Rostedt <srostedt@redhat.com>

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>
---
kernel/trace/ring_buffer.c | 25 +++++++++----------------
1 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a1ca495..0d64c51 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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);
--
1.6.5



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