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authorSteven Rostedt <srostedt@redhat.com>2008-12-23 11:32:25 -0500
committerIngo Molnar <mingo@elte.hu>2008-12-23 18:45:26 +0100
commit98db8df777438e16ad0f44a0fba05ebbdb73db8d (patch)
treef2cde3dbe3000f4bafd0c42df43f736b7e5a648b /kernel/trace
parenta8ccf1d6f60e3e6ae63122e02378cd4d40dd4aac (diff)
ring-buffer: prevent false positive warning
Impact: eliminate false WARN_ON message If an interrupt goes off after the setting of the local variable tail_page and before incrementing the write index of that page, the interrupt could push the commit forward to the next page. Later a check is made to see if interrupts pushed the buffer around the entire ring buffer by comparing the next page to the last commited page. This can produce a false positive if the interrupt had pushed the commit page forward as stated above. Thanks to Jiaying Zhang for finding this race. Reported-by: Jiaying Zhang <jiayingz@google.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Cc: <stable@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/ring_buffer.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d03f4f44a823..76f34c0ef29c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -962,12 +962,15 @@ static struct ring_buffer_event *
__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
unsigned type, unsigned long length, u64 *ts)
{
- struct buffer_page *tail_page, *head_page, *reader_page;
+ struct buffer_page *tail_page, *head_page, *reader_page, *commit_page;
unsigned long tail, write;
struct ring_buffer *buffer = cpu_buffer->buffer;
struct ring_buffer_event *event;
unsigned long flags;
+ commit_page = cpu_buffer->commit_page;
+ /* we just need to protect against interrupts */
+ barrier();
tail_page = cpu_buffer->tail_page;
write = local_add_return(length, &tail_page->write);
tail = write - length;
@@ -993,7 +996,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
* it all the way around the buffer, bail, and warn
* about it.
*/
- if (unlikely(next_page == cpu_buffer->commit_page)) {
+ if (unlikely(next_page == commit_page)) {
WARN_ON_ONCE(1);
goto out_unlock;
}