Hi Paul, 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. >> Unfortunately I cannot reproduce it with CONFIG_PROVE_RCU=y. >> >> I started seeing the issue when disabling an innocent option in >> shmobile_defconfig. I tracked it down to the removal of an unused C function, >> containing hardware support for another system. Replacing the C function by >> a dummy function with the right number of "asm("nop")"s (depending on kernel >> version and/or kernel config, sigh) made the issue go away. >> Adding or removing nops makes the issue reappear, and has some impact on >> how early the issue happens (sometimes as late as early userspace). >> Adding a multiple of 16 nops has no impact. >> So it looks like something that should be cacheline-aligned isn't... > > The other possibility is that it is timing related. Either way, fun > to find... > >> CONFIG_TREE_RCU=y >> >> Do you have a suggestion? > > Only trying Ding's patch... Thanks for the pointer anyway! 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
