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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: 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: printed:
INFO: rcu_preempt detected stall on CPU 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) (t=65000 jiffies)
The "(64628 ticks this GP)" indicates that this CPU has taken more 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 be a small positive number if in the idle loop and a very large positive
number (as shown above) otherwise. number (as shown above) otherwise.
For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the CPU is
CPU is not in the process of trying to force itself into dyntick-idle not in the process of trying to force itself into dyntick-idle state, the
state, the "." indicates that the CPU has not given up forcing RCU "." indicates that the CPU has not given up forcing RCU into dyntick-idle
into dyntick-idle mode (it would be "H" otherwise), and the "timer=-1" mode (it would be "H" otherwise), and the "timer not pending" indicates
indicates that the CPU has not recented forced RCU into dyntick-idle that the CPU has not recently forced RCU into dyntick-idle mode (it
mode (it would otherwise indicate the number of microseconds remaining would otherwise indicate the number of microseconds remaining in this
in this forced state). forced state).
Multiple Warnings From One Stall Multiple Warnings From One Stall

12
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 rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
struct timer_list *tltp = &rdtp->idle_gp_timer; struct timer_list *tltp = &rdtp->idle_gp_timer;
char c;
sprintf(cp, "drain=%d %c timer=%lu", c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.';
rdtp->dyntick_drain, if (timer_pending(tltp))
rdtp->dyntick_holdoff == jiffies ? 'H' : '.', sprintf(cp, "drain=%d %c timer=%lu",
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 */ #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */