A hrtimer can be released in its callback, but lockdep_hrtimer_exit()
dereferences the pointer after the callback returns, i.e. a potential use
after free.
Retrieve the context in which the hrtimer expires before the callback is
invoked and use it in lockdep_hrtimer_exit().
Fixes: 40db173965 ("lockdep: Add hrtimer context tracing bits")
Reported-by: syzbot+62c155c276e580cfb606@syzkaller.appspotmail.com
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200331201849.fkp2siy3vcdqvqlz@linutronix.de
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