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authorSteven Rostedt <srostedt@redhat.com>2008-12-23 11:32:25 -0500
committerIngo Molnar <mingo@elte.hu>2008-12-23 12:45:26 -0500
commit98db8df777438e16ad0f44a0fba05ebbdb73db8d (patch)
treef2cde3dbe3000f4bafd0c42df43f736b7e5a648b /kernel
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')
-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 *
962__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer, 962__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
963 unsigned type, unsigned long length, u64 *ts) 963 unsigned type, unsigned long length, u64 *ts)
964{ 964{
965 struct buffer_page *tail_page, *head_page, *reader_page; 965 struct buffer_page *tail_page, *head_page, *reader_page, *commit_page;
966 unsigned long tail, write; 966 unsigned long tail, write;
967 struct ring_buffer *buffer = cpu_buffer->buffer; 967 struct ring_buffer *buffer = cpu_buffer->buffer;
968 struct ring_buffer_event *event; 968 struct ring_buffer_event *event;
969 unsigned long flags; 969 unsigned long flags;
970 970
971 commit_page = cpu_buffer->commit_page;
972 /* we just need to protect against interrupts */
973 barrier();
971 tail_page = cpu_buffer->tail_page; 974 tail_page = cpu_buffer->tail_page;
972 write = local_add_return(length, &tail_page->write); 975 write = local_add_return(length, &tail_page->write);
973 tail = write - length; 976 tail = write - length;
@@ -993,7 +996,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
993 * it all the way around the buffer, bail, and warn 996 * it all the way around the buffer, bail, and warn
994 * about it. 997 * about it.
995 */ 998 */
996 if (unlikely(next_page == cpu_buffer->commit_page)) { 999 if (unlikely(next_page == commit_page)) {
997 WARN_ON_ONCE(1); 1000 WARN_ON_ONCE(1);
998 goto out_unlock; 1001 goto out_unlock;
999 } 1002 }