From 467b9b729d746c37c8597a37603b6de3c3ec53b0 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 14 Oct 2011 10:44:25 -0400 Subject: [PATCH] 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 Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 8a58f5196f27..a3f3d0cf2daf 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3624,8 +3624,6 @@ 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, @@ -3640,6 +3638,8 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, if (pos < PAGE_SIZE) memset(info->spare + pos, 0, PAGE_SIZE - pos); + info->read = 0; + read: size = PAGE_SIZE - info->read; if (size > count) -- 2.39.2