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    SubjectRe: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i_private
    On 07/18, Masami Hiramatsu wrote:
    >
    > (2013/07/17 23:51), Oleg Nesterov wrote:
    > > Well, perhaps you are right... But this TRACE_EVENT_FL_REF_MASK code
    > > is new too, it is not that we only need a small fixlets to finish it.
    >
    > Would you mean that TRACE_EVENT_FL_REF_MASK may also have some problems?

    It was you who initially pointed that it does have problems ;)

    And, _afaics_ your patch which tries to fix this problem is not
    exactly correct.

    It removes trace_array_get/put from tracing_open_generic_file() and
    tracing_release_generic_file(). This assumes that "call->flags++" is
    enough, but it is not.

    Yes, the next patch adds the "flags & TRACE_EVENT_FL_REF_MASK" check
    into trace_remove_event_call() path. But this is still racy wrt
    instance_delete() unless I missed something.

    IOW, I believe that either .open() should do trace_array_get(), or
    __trace_remove_event_dirs() needs another for-each-file loop which
    checks file->call->flags & TRACE_EVENT_FL_REF_MASK.


    > > So I think that it makes sense to discuss the alternatives before we
    > > decide what exactly we should do.
    >
    > Your approach is also interesting for me, indeed. However, it is so
    > different from current one. I think you should clarify what bug you
    > would like to solve and how.

    The same bugs which Steven's 1/4 tries to solve ;)

    Oleg.



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