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    SubjectRe: [PATCH 1/4] rtmutex: avoid null derefence in WARN_ON
    On 07/09/2010 05:29 PM, Steven Rostedt wrote:
    > On Fri, 2010-07-09 at 15:32 -0700, Darren Hart wrote:
    >> If the pi_blocked_on variable is NULL, the subsequent WARN_ON's
    >> will cause an OOPS. Only perform the susequent checks if
    >> pi_blocked_on is valid.
    >>
    >> Signed-off-by: Darren Hart<dvhltc@us.ibm.com>
    >> Cc: Thomas Gleixner<tglx@linutronix.de>
    >> Cc: Peter Zijlstra<peterz@infradead.org>
    >> Cc: Ingo Molnar<mingo@elte.hu>
    >> Cc: Eric Dumazet<eric.dumazet@gmail.com>
    >> Cc: John Kacur<jkacur@redhat.com>
    >> Cc: Steven Rostedt<rostedt@goodmis.org>
    >> Cc: Mike Galbraith<efault@gmx.de>
    >> ---
    >> kernel/rtmutex.c | 7 ++++---
    >> 1 files changed, 4 insertions(+), 3 deletions(-)
    >>
    >> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
    >> index 23dd443..baac7d9 100644
    >> --- a/kernel/rtmutex.c
    >> +++ b/kernel/rtmutex.c
    >> @@ -579,9 +579,10 @@ static void wakeup_next_waiter(struct rt_mutex *lock, int savestate)
    >>
    >> raw_spin_lock(&pendowner->pi_lock);
    >>
    >> - WARN_ON(!pendowner->pi_blocked_on);
    >> - WARN_ON(pendowner->pi_blocked_on != waiter);
    >> - WARN_ON(pendowner->pi_blocked_on->lock != lock);
    >> + if (!WARN_ON(!pendowner->pi_blocked_on)) {
    >> + WARN_ON(pendowner->pi_blocked_on != waiter);
    >
    > The above actually has no issue if the pi_blocked_on is NULL.

    It doesn't, but it's also redundant and makes the console noisier for no
    reason. Seemed worth while to drop it under the if in the same go.

    --
    Darren


    > The below, well yeah.
    >
    > -- Steve
    >
    >> + WARN_ON(pendowner->pi_blocked_on->lock != lock);
    >> + }
    >>
    >> pendowner->pi_blocked_on = NULL;
    >>
    >
    >


    --
    Darren Hart
    IBM Linux Technology Center
    Real-Time Linux Team


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