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authorSteven Rostedt <srostedt@redhat.com>2012-11-29 22:31:16 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-01-17 08:50:51 -0800
commit4d7981bfc21f7b6ef48f9a819d2c9969ad6eea71 (patch)
treebcfce7dceeba920d49de2f696b1f12380818bafc /kernel
parent0d38a8789caf511e5b997caf76eb32fddbff051c (diff)
ring-buffer: Fix race between integrity check and readers
commit 9366c1ba13fbc41bdb57702e75ca4382f209c82f upstream. The function rb_check_pages() was added to make sure the ring buffer's pages were sane. This check is done when the ring buffer size is modified as well as when the iterator is released (closing the "trace" file), as that was considered a non fast path and a good place to do a sanity check. The problem is that the check does not have any locks around it. If one process were to read the trace file, and another were to read the raw binary file, the check could happen while the reader is reading the file. The issues with this is that the check requires to clear the HEAD page before doing the full check and it restores it afterward. But readers require the HEAD page to exist before it can read the buffer, otherwise it gives a nasty warning and disables the buffer. By adding the reader lock around the check, this keeps the race from happening. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 cf8d11e91efd..28667834181e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2708,7 +2708,7 @@ unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
unsigned long flags;
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *bpage;
- unsigned long ret;
+ unsigned long ret = 0;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
@@ -2723,7 +2723,8 @@ unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
bpage = cpu_buffer->reader_page;
else
bpage = rb_set_head_page(cpu_buffer);
- ret = bpage->page->time_stamp;
+ if (bpage)
+ ret = bpage->page->time_stamp;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return ret;
@@ -3030,6 +3031,8 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
* Splice the empty reader page into the list around the head.
*/
reader = rb_set_head_page(cpu_buffer);
+ if (!reader)
+ goto out;
cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
cpu_buffer->reader_page->list.prev = reader->list.prev;