lkml.org 
[lkml]   [2020]   [Apr]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.19 22/40] tracing: Fix the race between registering snapshot event trigger and triggering snapshot operation
    Date
    From: Xiao Yang <yangx.jy@cn.fujitsu.com>

    commit 0bbe7f719985efd9adb3454679ecef0984cb6800 upstream.

    Traced event can trigger 'snapshot' operation(i.e. calls snapshot_trigger()
    or snapshot_count_trigger()) when register_snapshot_trigger() has completed
    registration but doesn't allocate buffer for 'snapshot' event trigger. In
    the rare case, 'snapshot' operation always detects the lack of allocated
    buffer so make register_snapshot_trigger() allocate buffer first.

    trigger-snapshot.tc in kselftest reproduces the issue on slow vm:
    -----------------------------------------------------------
    cat trace
    ...
    ftracetest-3028 [002] .... 236.784290: sched_process_fork: comm=ftracetest pid=3028 child_comm=ftracetest child_pid=3036
    <...>-2875 [003] .... 240.460335: tracing_snapshot_instance_cond: *** SNAPSHOT NOT ALLOCATED ***
    <...>-2875 [003] .... 240.460338: tracing_snapshot_instance_cond: *** stopping trace here! ***
    -----------------------------------------------------------

    Link: http://lkml.kernel.org/r/20200414015145.66236-1-yangx.jy@cn.fujitsu.com

    Cc: stable@vger.kernel.org
    Fixes: 93e31ffbf417a ("tracing: Add 'snapshot' event trigger command")
    Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/trace/trace_events_trigger.c | 10 +++-------
    1 file changed, 3 insertions(+), 7 deletions(-)

    --- a/kernel/trace/trace_events_trigger.c
    +++ b/kernel/trace/trace_events_trigger.c
    @@ -1081,14 +1081,10 @@ register_snapshot_trigger(char *glob, st
    struct event_trigger_data *data,
    struct trace_event_file *file)
    {
    - int ret = register_trigger(glob, ops, data, file);
    + if (tracing_alloc_snapshot_instance(file->tr) != 0)
    + return 0;

    - if (ret > 0 && tracing_alloc_snapshot_instance(file->tr) != 0) {
    - unregister_trigger(glob, ops, data, file);
    - ret = 0;
    - }
    -
    - return ret;
    + return register_trigger(glob, ops, data, file);
    }

    static int

    \
     
     \ /
      Last update: 2020-04-20 14:51    [W:4.109 / U:0.364 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site