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    SubjectRe: [PATCH] ftrace: Avoid double-free of dyn_ftrace

    On Fri, 13 Mar 2009, Zhaolei wrote:

    > * From: "Ingo Molnar" <mingo@elte.hu>
    > >
    > > * Zhaolei <zhaolei@cn.fujitsu.com> wrote:
    > >
    > >> If dyn_ftrace is free before ftrace_release(),
    > >> ftrace_release() will free it again and make
    > >> ftrace_free_records wrong.
    > >>
    > >> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
    > >> ---
    > >> kernel/trace/ftrace.c | 3 ++-
    > >> 1 files changed, 2 insertions(+), 1 deletions(-)
    > >>
    > >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
    > >> index d33d306..26c45aa 100644
    > >> --- a/kernel/trace/ftrace.c
    > >> +++ b/kernel/trace/ftrace.c
    > >> @@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
    > >>
    > >> mutex_lock(&ftrace_lock);
    > >> do_for_each_ftrace_rec(pg, rec) {
    > >> - if ((rec->ip >= s) && (rec->ip < e))
    > >> + if ((rec->ip >= s) && (rec->ip < e) &&
    > >> + !(rec->flags & FTRACE_FL_FREE))
    > >> ftrace_free_rec(rec);
    > >
    > > Applied to tip:tracing/ftrace, thanks!
    > >
    > > I'm wondering, did you trigger this in practice (if yes, how?),
    > > or have you found it via code review?
    > Hello, Ingo
    >
    > It is found via code review.

    Hmm, could you explain this more. I'm thinking that this scenario should
    not happen, and if it does, it should probably be a bug.

    Because when we call ftrace_free_rec we change the rec->ip to point to the
    next record in the chain. Something is very wrong if rec->ip >= s &&
    rec->ip < e and the record is already free.

    We can add a:

    WARN_ON(rec->flags & FTRACE_FL_FREE);

    in ftrace_free_rec if you are worried about this happening.

    -- Steve



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