Re: [PATCH] futex: Fix hrtimer oops in futex_lock_pi()

[Tony Lindgren]

* Tony Lindgren <tony@xxxxxxxxxxx> [170414 07:28]:
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> [170414 07:25]:
> > On Fri, Apr 14, 2017 at 07:08:19AM -0700, Tony Lindgren wrote:
> > > Commit cfafcd117da0 ("futex: Rework futex_lock_pi() to use
> > > rt_mutex_*_proxy_lock()") caused a regression where things would
> > > occasionally randomly oops when restarting X:
> > > 
> > > Unable to handle kernel NULL pointer dereference at virtual address 00000000
> > > ...
> > > Internal error: Oops: 80000005 [#1] SMP ARM
> > > ...
> > > PC is at 0x0
> > > LR is at __hrtimer_run_queues+0x138/0x58c
> > > pc : [<00000000>]    lr : [<c01c7884>]    psr: 20000193
> > > ...
> > > [<c01c7884>] (__hrtimer_run_queues) from [<c01c7f4c>]
> > > (hrtimer_interrupt+0xbc/0x210)
> > > [<c01c7f4c>] (hrtimer_interrupt) from [<c010fcfc>]
> > > ...
> > > 
> > > When this happens, the hrtimer is not properly initialized and it's
> > > function is NULL. This happens because we now call hrtimer_start_expires()
> > > in futex_lock_pi() for the timer initialized with hrtimer_init_on_stack().
> > > 
> > > To fix it, let's pair the hrtimer_start_expires() with hrtimer_cancel()
> > > in the same function.
> > 
> > Already fixed:
> > 
> >   https://lkml.kernel.org/r/tip-97181f9bd57405b879403763284537e27d46963d@xxxxxxxxxxxxxx
> > 
> > Thanks for the patch though.
> 
> Oh OK thanks. It seems to be missing in Linux next though.

Oh it was just committed, I see it now in tip after git fetch.
So should be heading into nex soon.

Tony