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authorSteven Rostedt <srostedt@redhat.com>2011-10-14 10:44:25 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2011-11-11 09:35:53 -0800
commit12cb3e734a5616ea0057aee938c553ff6ccbdfbd (patch)
tree828c560746757c997c97a76777444a036a5ef9ac /kernel/trace
parentd59892017c5f6de2fdee221f2a7788696e9f2cda (diff)
tracing: Fix returning of duplicate data after EOF in trace_pipe_raw
commit 436fc280261dcfce5af38f08b89287750dc91cd2 upstream. The trace_pipe_raw handler holds a cached page from the time the file is opened to the time it is closed. The cached page is used to handle the case of the user space buffer being smaller than what was read from the ring buffer. The left over buffer is held in the cache so that the next read will continue where the data left off. After EOF is returned (no more data in the buffer), the index of the cached page is set to zero. If a user app reads the page again after EOF, the check in the buffer will see that the cached page is less than page size and will return the cached page again. This will cause reading the trace_pipe_raw again after EOF to return duplicate data, making the output look like the time went backwards but instead data is just repeated. The fix is to not reset the index right after all data is read from the cache, but to reset it after all data is read and more data exists in the ring buffer. Reported-by: Jeremy Eder <jeder@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/trace.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ee9c921d7f21..0731e81a5bbd 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3704,8 +3704,6 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
if (info->read < PAGE_SIZE)
goto read;
- info->read = 0;
-
trace_access_lock(info->cpu);
ret = ring_buffer_read_page(info->tr->buffer,
&info->spare,
@@ -3715,6 +3713,8 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
if (ret < 0)
return 0;
+ info->read = 0;
+
read:
size = PAGE_SIZE - info->read;
if (size > count)