On Sat, Apr 26, 2014 at 11:26:50PM -0700, Paul E. McKenney wrote:
> On Fri, Apr 25, 2014 at 01:52:30PM -0700, Randy Dunlap wrote:
> > On 04/25/14 13:44, Randy Dunlap wrote:
> > > On 04/25/14 07:04, Rik van Riel wrote:
> > >> On Thu, 24 Apr 2014 15:40:29 -0700
> > >> Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
> > >>
> > >>
> > >>> uml on x86_64 defconfig:
> > >>>
> > >>> drivers/built-in.o: In function `__handle_sysrq':
> > >>> drivers/tty/sysrq.c:514: undefined reference to `rcu_sysrq_start'
> > >>> drivers/tty/sysrq.c:558: undefined reference to `rcu_sysrq_end'
> > >>
> > >> Randy, does the patch below fix it?
> >
> > CONFIG_TINY_RCU=y
> >
> > tiny.c does not provide these functions... Paul...
> >
> > > Hm, no, it does not. I'll look into it.
> > >
> > >> Mike, this patch should also address your concerns.
> > >>
> > >> Andrew, this can be a -fix patch for the sysctl-rcu patch,
> > >> assuming it fixes things :)
> > >>
> > >> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx
> > >> ---
> > >> drivers/tty/sysrq.c | 1 +
> > >> kernel/rcu/update.c | 3 ++-
> > >> 2 files changed, 3 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> > >> index dd53af9..0867433 100644
> > >> --- a/drivers/tty/sysrq.c
> > >> +++ b/drivers/tty/sysrq.c
> > >> @@ -46,6 +46,7 @@
> > >> #include <linux/jiffies.h>
> > >> #include <linux/syscalls.h>
> > >> #include <linux/of.h>
> > >> +#include <linux/rcupdate.h>
> > >>
> > >> #include <asm/ptrace.h>
> > >> #include <asm/irq_regs.h>
> > >> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> > >> index 2ac3289..d22309c 100644
> > >> --- a/kernel/rcu/update.c
> > >> +++ b/kernel/rcu/update.c
> > >> @@ -322,7 +322,8 @@ int rcu_jiffies_till_stall_check(void)
> > >>
> > >> void rcu_sysrq_start(void)
> > >> {
> > >> - rcu_cpu_stall_suppress = 2;
> > >> + if (!rcu_cpu_stall_suppress)
> > >> + rcu_cpu_stall_suppress = 2;
> > >> }
> > >>
> > >> void rcu_sysrq_end(void)
>
> You would think that I would have learned by now that RCU requires a bit
> more care... Anyway, patch containing only the APIs that -should- work
> is below. Currently testing it on the usual set of configs.
Right... Adding a "static inline" would help, wouldn't it? Updated
patch below.
Thanx, Paul
------------------------------------------------------------------------
rcu: Provide API to suppress stall warnings while sysrc runs
Some sysrq handlers can run for a long time, because they dump a lot
of data onto a serial console. Having RCU stall warnings pop up in
the middle of them only makes the problem worse.
This commit provides rcu_sysrq_start() and rcu_sysrq_end() APIs to
temporarily suppress RCU CPU stall warnings while a sysrq request is
handled.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
[ paulmck: Fix TINY_RCU build error. ]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a6f2664a1b77..ca6fe55913b7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -248,6 +248,18 @@ void rcu_idle_exit(void);
void rcu_irq_enter(void);
void rcu_irq_exit(void);
+#ifdef CONFIG_RCU_STALL_COMMON
+void rcu_sysrq_start(void);
+void rcu_sysrq_end(void);
+#else /* #ifdef CONFIG_RCU_STALL_COMMON */
+static inline void rcu_sysrq_start(void)
+{
+}
+static inline void rcu_sysrq_end(void)
+{
+}
+#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
+
#ifdef CONFIG_RCU_USER_QS
void rcu_user_enter(void);
void rcu_user_exit(void);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index ed7a0d72562c..a2aeb4df0f60 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -320,6 +320,18 @@ int rcu_jiffies_till_stall_check(void)
return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}
+void rcu_sysrq_start(void)
+{
+ if (!rcu_cpu_stall_suppress)
+ rcu_cpu_stall_suppress = 2;
+}
+
+void rcu_sysrq_end(void)
+{
+ if (rcu_cpu_stall_suppress == 2)
+ rcu_cpu_stall_suppress = 0;
+}
+
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
{
rcu_cpu_stall_suppress = 1;
--
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