Hi Paul, On Fri, Jan 22, 2016 at 9:44 PM, Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > On Fri, Jan 22, 2016 at 09:55:44AM +0100, Geert Uytterhoeven wrote: >> On Thu, Jan 21, 2016 at 5:06 PM, Paul E. McKenney >> <paulmck@xxxxxxxxxxxxxxxxxx> wrote: >> > On Thu, Jan 21, 2016 at 02:22:56PM +0100, Geert Uytterhoeven wrote: >> >> On Thu, Dec 10, 2015 at 12:10 AM, Paul E. McKenney >> >> <paulmck@xxxxxxxxxxxxxxxxxx> wrote: >> >> > This commit replaces a local_irq_save()/local_irq_restore() pair with >> >> > a lockdep assertion that interrupts are already disabled. This should >> >> > remove the corresponding overhead from the interrupt entry/exit fastpaths. >> >> > >> >> > This change was inspired by the fact that Iftekhar Ahmed's mutation >> >> > testing showed that removing rcu_irq_enter()'s call to local_ird_restore() >> >> > had no effect, which might indicate that interrupts were always enabled >> >> > anyway. >> >> > >> >> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> >> >> > --- >> >> > include/linux/rcupdate.h | 4 ++-- >> >> > include/linux/rcutiny.h | 8 ++++++++ >> >> > include/linux/rcutree.h | 2 ++ >> >> > include/linux/tracepoint.h | 4 ++-- >> >> > kernel/rcu/tree.c | 32 ++++++++++++++++++++++++++------ >> >> > 5 files changed, 40 insertions(+), 10 deletions(-) >> >> >> >> This commit (7c9906ca5e582a773fff696975e312cef58a7386) is triggering lock ups >> >> during boot on r8a7791/koelsch (dual Cortex A15). Probably this commit does not >> >> contain the real bug, but a symptom. >> > >> > On the off-chance that it is related, here is Ding Tianhong's patch >> > that addressed some lockups: >> > >> > http://www.eenyhelp.com/patch-rfc-locking-mutexes-dont-spin-owner-when-wait-list-not-null-help-215929641.html >> > >> > Does that help in your case? >> >> Unfortunately not. > > We could revert the RCU patch without any real problems -- it is after > all just an optimization. I replaced the calls to rcu_irq_{enter,exit}() in irq_{enter,exit}() by their _irqson counterparts, which should be equivalent to the old code, but the issue persisted. Strange... Does it matter that arm has #define __ARCH_IRQ_EXIT_IRQS_DISABLED 1 ? I tried JTAG, but enabling JTAG on r8a7791/koelsch requires changing a switch on the board, which also disables the second CPU core, and thus makes the issue disappear... > Hmmm... One issue that we have seen before is that the irq-disabled > indication is a software flag that is not always in sync with > hardware conditions. Might it be that we are hitting a situation where > irqs_disabled() is giving the wrong answer, thus suppressing the lockdep > warning? Possible. I tried adding 'if(!irqs_disabled) printk("something")' just before the RCU_LOCKDEP_WARN(), but it never triggered. Worse, the issue went away by doing that :-( Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
