Commit-ID: 62f0b3eb5cb58931a02ee4e599e19c80a171e351
Gitweb: http://git.kernel.org/tip/62f0b3eb5cb58931a02ee4e599e19c80a171e351
Author: Steven Rostedt <srostedt@xxxxxxxxxx>
AuthorDate: Fri, 4 Sep 2009 14:11:34 -0400
Committer: Steven Rostedt <rostedt@xxxxxxxxxxx>
CommitDate: Fri, 4 Sep 2009 19:38:42 -0400
ring-buffer: check for swapped buffers in start of committing
Because the irqsoff tracer can swap an internal CPU buffer, it is possible
that a swap happens between the start of the write and before the committing
bit is set (the committing bit will disable swapping).
This patch adds a check for this and will fail the write if it detects it.
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
kernel/trace/ring_buffer.c | 20 +++++++++++++++++---
1 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f83a42a..1766c0e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2073,7 +2073,8 @@ static void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
}
static struct ring_buffer_event *
-rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
+rb_reserve_next_event(struct ring_buffer *buffer,
+ struct ring_buffer_per_cpu *cpu_buffer,
unsigned long length)
{
struct ring_buffer_event *event;
@@ -2083,6 +2084,19 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
rb_start_commit(cpu_buffer);
+ /*
+ * Due to the ability to swap a cpu buffer from a buffer
+ * it is possible it was swapped before we committed.
+ * (committing stops a swap). We check for it here and
+ * if it happened, we have to fail the write.
+ */
+ barrier();
+ if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
+ local_dec(&cpu_buffer->committing);
+ local_dec(&cpu_buffer->commits);
+ return NULL;
+ }
+
length = rb_calculate_event_length(length);
again:
/*
@@ -2243,7 +2257,7 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
if (length > BUF_MAX_DATA_SIZE)
goto out;
- event = rb_reserve_next_event(cpu_buffer, length);
+ event = rb_reserve_next_event(buffer, cpu_buffer, length);
if (!event)
goto out;
@@ -2476,7 +2490,7 @@ int ring_buffer_write(struct ring_buffer *buffer,
if (length > BUF_MAX_DATA_SIZE)
goto out;
- event = rb_reserve_next_event(cpu_buffer, length);
+ event = rb_reserve_next_event(buffer, cpu_buffer, length);
if (!event)
goto out;
--
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