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authorSteven Rostedt <srostedt@redhat.com>2011-10-14 10:44:25 -0400
committerSteven Rostedt <rostedt@goodmis.org>2011-10-14 10:44:25 -0400
commit436fc280261dcfce5af38f08b89287750dc91cd2 (patch)
tree5a57ba115f7f9d19c0185673fa1bfba9dfc292da /kernel
parent9b5f8b31af57a8ce9e9f77864d9143b5e3304815 (diff)
tracing: Fix returning of duplicate data after EOF in trace_pipe_raw
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. Cc: stable <stable@kernel.org> Reported-by: Jeremy Eder <jeder@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-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 cea16053f553..b24a72d35008 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3903,8 +3903,6 @@ 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,
@@ -3914,6 +3912,8 @@ 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)