Messages in this thread |  | | | Date | Sat, 14 Oct 2006 02:54:50 +0530 | | From | Dipankar Sarma <> | | Subject | Re: 2.6.18-rt1 |
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On Fri, Oct 13, 2006 at 11:18:01PM +0200, Karsten Wiese wrote: > Am Samstag, 30. September 2006 20:18 schrieb Dipankar Sarma: > > On Sat, Sep 30, 2006 at 02:06:04PM -0400, Lee Revell wrote: > > > On Wed, 2006-09-20 at 16:19 +0200, Ingo Molnar wrote: > > > > I'm pleased to announce the 2.6.18-rt1 tree, which can be downloaded > > > > from the usual place: > > > > > > > > http://redhat.com/~mingo/realtime-preempt/ > > > > > > I got this Oops with -rt3, looks RCU related. Apologies in advance if > > > it's already known. > > > > > > Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP: > > > [<ffffffff802aafa7>] __rcu_read_unlock+0x2e/0x82 > > > PGD 46a3067 PUD 4e27067 PMD 0 > > > Oops: 0002 [1] PREEMPT SMP > > > CPU 1 > > > > I see a very similar crash while running rcutorture on 2.6.18-mm1 and > > my rcu patchset that has rcupreempt stuff rom -rt. I don't see this > > > > Bug just happened here on a tainted UP x86_64 running rt4. > IIRC this is the second time in 2 weeks or so. > Machine seams to be fine still after the oops... > > <Oops> > Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP: > [<ffffffff802a1b21>] __rcu_read_unlock+0x2e/0x80 > PGD 3b616067 PUD 1718b067 PMD 0 > Oops: 0002 [1] PREEMPT > CPU 0 > Modules linked in: autofs4 sunrpc video button ac lp parport_pc parport nvram snd_via82xx gameport snd_ac97_codec snd_ac97_bus snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq nvidia snd_pcm_oss snd_mixer_oss snd_pcm ehci_hcd uhci_hcd snd_timer snd_page_alloc snd_mpu401_uart snd_rawmidi pcspkr snd_seq_device snd i2c_viapro i2c_core r8169 soundcore ext3 jbd > Pid: 7102, comm: sh Tainted: P 2.6.18-rt4 #4 > RIP: 0010:[<ffffffff802a1b21>] [<ffffffff802a1b21>] __rcu_read_unlock+0x2e/0x80
Sorry, I should have published my investigations long ago. I tracked this down (atleast the crash in my machine) to NMI interference with rcu_read_lock()/rcu_read_unlock(). We use those APIs from NMI context as well (default_do_nmi()->notify_die()->atomic_notifier_call_chain()).
Can you try with nmi_watchdog=0 in the kernel command line ?
Paul has an NMI-safe patch for rcupreempt which I am adopting and testing at the moment. If this works well, I will publish a new patchset.
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