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    Subject[PATCH 3.2 138/152] tracing: Move mutex to protect against resetting of seq data
    3.2.84-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

    commit 1245800c0f96eb6ebb368593e251d66c01e61022 upstream.

    The iter->seq can be reset outside the protection of the mutex. So can
    reading of user data. Move the mutex up to the beginning of the function.

    Fixes: d7350c3f45694 ("tracing/core: make the read callbacks reentrants")
    Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    [bwh: Backported to 3.2: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    kernel/trace/trace.c | 15 ++++++++-------
    1 file changed, 8 insertions(+), 7 deletions(-)

    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -3331,13 +3331,6 @@ tracing_read_pipe(struct file *filp, cha
    static struct tracer *old_tracer;
    ssize_t sret;

    - /* return any leftover data */
    - sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
    - if (sret != -EBUSY)
    - return sret;
    -
    - trace_seq_init(&iter->seq);
    -
    /* copy the tracer to avoid using a global lock all around */
    mutex_lock(&trace_types_lock);
    if (unlikely(old_tracer != current_trace && current_trace)) {
    @@ -3352,6 +3345,14 @@ tracing_read_pipe(struct file *filp, cha
    * is protected.
    */
    mutex_lock(&iter->mutex);
    +
    + /* return any leftover data */
    + sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
    + if (sret != -EBUSY)
    + goto out;
    +
    + trace_seq_init(&iter->seq);
    +
    if (iter->trace->read) {
    sret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
    if (sret)
    \
     
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