On Thu, Jan 21, 2016 at 02:22:56PM +0100, Geert Uytterhoeven wrote: > Hi Paul, > > 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 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... Thanx, Paul
