• Steven Rostedt's avatar
    tracing: Fix returning of duplicate data after EOF in trace_pipe_raw · 436fc280
    Steven Rostedt authored
    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: default avatarJeremy Eder <jeder@redhat.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    436fc280
trace.c 110 KB