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Commit 86f343b5 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
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rcu: Fix CONFIG_RCU_FAST_NO_HZ stall warning message 



The print_cpu_stall_fast_no_hz() function attempts to print -1 when
the ->idle_gp_timer is not pending, but unsigned arithmetic causes it
to instead print ULONG_MAX, which is 4294967295 on 32-bit systems and
18446744073709551615 on 64-bit systems.  Neither of these are the most
reader-friendly values, so this commit instead causes "timer not pending"
to be printed when ->idle_gp_timer is not pending.

Reported-by: default avatarPaul Walmsley <paul@pwsan.com>
Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 22a76726

Documentation/RCU/stallwarn.txt

+8 −8
Original line number Diff line number Diff line
@@ -99,7 +99,7 @@ In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is 
printed:



	INFO: rcu_preempt detected stall on CPU

	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer=-1

	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer not pending

	   (t=65000 jiffies)



The "(64628 ticks this GP)" indicates that this CPU has taken more
@@ -116,13 +116,13 @@ number between the two "/"s is the value of the nesting, which will 
be a small positive number if in the idle loop and a very large positive

number (as shown above) otherwise.



For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the

CPU is not in the process of trying to force itself into dyntick-idle

state, the "." indicates that the CPU has not given up forcing RCU

into dyntick-idle mode (it would be "H" otherwise), and the "timer=-1"

indicates that the CPU has not recented forced RCU into dyntick-idle

mode (it would otherwise indicate the number of microseconds remaining

in this forced state).

For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the CPU is

not in the process of trying to force itself into dyntick-idle state, the

"." indicates that the CPU has not given up forcing RCU into dyntick-idle

mode (it would be "H" otherwise), and the "timer not pending" indicates

that the CPU has not recently forced RCU into dyntick-idle mode (it

would otherwise indicate the number of microseconds remaining in this

forced state).





Multiple Warnings From One Stall

kernel/rcutree_plugin.h

+8 −4
Original line number Diff line number Diff line
@@ -2130,11 +2130,15 @@ static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 
{

	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

	struct timer_list *tltp = &rdtp->idle_gp_timer;

	char c;



	c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.';

	if (timer_pending(tltp))

		sprintf(cp, "drain=%d %c timer=%lu",

		rdtp->dyntick_drain,

		rdtp->dyntick_holdoff == jiffies ? 'H' : '.',

		timer_pending(tltp) ? tltp->expires - jiffies : -1);

			rdtp->dyntick_drain, c, tltp->expires - jiffies);

	else

		sprintf(cp, "drain=%d %c timer not pending",

			rdtp->dyntick_drain, c);

}



#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */