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    Subject[for-next-3.11][PATCH 1/8] tracing: Turn event/id->i_private into call->event.type
    From: Oleg Nesterov <oleg@redhat.com>

    event_id_read() is racy, ftrace_event_call can be already freed
    by trace_remove_event_call() callers.

    Change event_create_dir() to pass "data = call->event.type", this
    is all event_id_read() needs. ftrace_event_id_fops no longer needs
    tracing_open_generic().

    We add the new helper, event_file_data(), to read ->i_private, it
    will have more users.

    Note: currently ACCESS_ONCE() and "id != 0" check are not needed,
    but we are going to change event_remove/rmdir to clear ->i_private.

    Link: http://lkml.kernel.org/r/20130726172532.GA3605@redhat.com

    Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    kernel/trace/trace_events.c | 18 +++++++++++++-----
    1 file changed, 13 insertions(+), 5 deletions(-)

    diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
    index 898f868..c2d13c5 100644
    --- a/kernel/trace/trace_events.c
    +++ b/kernel/trace/trace_events.c
    @@ -409,6 +409,11 @@ static void put_system(struct ftrace_subsystem_dir *dir)
    mutex_unlock(&event_mutex);
    }

    +static void *event_file_data(struct file *filp)
    +{
    + return ACCESS_ONCE(file_inode(filp)->i_private);
    +}
    +
    /*
    * Open and update trace_array ref count.
    * Must have the current trace_array passed to it.
    @@ -946,14 +951,18 @@ static int trace_format_open(struct inode *inode, struct file *file)
    static ssize_t
    event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
    {
    - struct ftrace_event_call *call = filp->private_data;
    + int id = (long)event_file_data(filp);
    char buf[32];
    int len;

    if (*ppos)
    return 0;

    - len = sprintf(buf, "%d\n", call->event.type);
    + if (unlikely(!id))
    + return -ENODEV;
    +
    + len = sprintf(buf, "%d\n", id);
    +
    return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
    }

    @@ -1240,7 +1249,6 @@ static const struct file_operations ftrace_event_format_fops = {
    };

    static const struct file_operations ftrace_event_id_fops = {
    - .open = tracing_open_generic,
    .read = event_id_read,
    .llseek = default_llseek,
    };
    @@ -1488,8 +1496,8 @@ event_create_dir(struct dentry *parent,

    #ifdef CONFIG_PERF_EVENTS
    if (call->event.type && call->class->reg)
    - trace_create_file("id", 0444, file->dir, call,
    - id);
    + trace_create_file("id", 0444, file->dir,
    + (void *)(long)call->event.type, id);
    #endif

    /*
    --
    1.7.10.4



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