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rcu: Fix CONFIG_RCU_FAST_NO_HZ stall warning message

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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: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-09-21 10:41:50 -07:00 committed by Paul E. McKenney
parent 22a767269a
commit 86f343b50b
2 changed files with 16 additions and 12 deletions
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16
Documentation/RCU/stallwarn.txt
View file

@ -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

10
kernel/rcutree_plugin.h
View file

@ -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 */