diff options
| author | Steven Rostedt <srostedt@redhat.com> | 2008-12-23 11:32:25 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2009-01-18 10:43:44 -0800 |
| commit | 6870fdf3a70ea33f544cb1474916bee1c366ce9d (patch) | |
| tree | 71d66fdc242a0c40525d14887f63f5a7718a848d /kernel/trace/ring_buffer.c | |
| parent | a94b68d6dcb74563d07c6eaf3f4b1191d0171e19 (diff) | |
ring-buffer: prevent false positive warning
commit 98db8df777438e16ad0f44a0fba05ebbdb73db8d upstream.
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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'kernel/trace/ring_buffer.c')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 668bbb5ef2b..2b75a581ea3 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -880,12 +880,15 @@ 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; @@ -909,7 +912,7 @@ __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; } |