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Commit f511fc624642f0bb8cf65aaa28979737514d4746

Authored by Paul E. McKenney
Committed by Paul E. McKenney
1 parent 79b9a75fb7
Exists in smarc-l5.0.0_1.0.0-ga and in 5 other branches imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga

rcu: Ensure that RCU_FAST_NO_HZ timers expire on correct CPU 

Timers are subject to migration, which can lead to the following
system-hang scenario when CONFIG_RCU_FAST_NO_HZ=y:

1.	CPU 0 executes synchronize_rcu(), which posts an RCU callback.

2.	CPU 0 then goes idle.  It cannot immediately invoke the callback,
	but there is nothing RCU needs from ti, so it enters dyntick-idle
	mode after posting a timer.

3.	The timer gets migrated to CPU 1.

4.	CPU 0 never wakes up, so the synchronize_rcu() never returns, so
	the system hangs.

This commit fixes this problem by using mod_timer_pinned(), as suggested
by Peter Zijlstra, to ensure that the timer is actually posted on the
running CPU.

Reported-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Showing 1 changed file with 8 additions and 5 deletions Side-by-side Diff

kernel/rcutree_plugin.h
Diff comments   View file @ f511fc6
... ... @@ -2110,6 +2110,8 @@
2110 2110 */
2111 2111 static void rcu_prepare_for_idle(int cpu)
2112 2112 {
  2113 + struct timer_list *tp;
  2114 +
2113 2115 /*
2114 2116 * If this is an idle re-entry, for example, due to use of
2115 2117 * RCU_NONIDLE() or the new idle-loop tracing API within the idle
... ... @@ -2121,9 +2123,10 @@
2121 2123 if (!per_cpu(rcu_idle_first_pass, cpu) &&
2122 2124 (per_cpu(rcu_nonlazy_posted, cpu) ==
2123 2125 per_cpu(rcu_nonlazy_posted_snap, cpu))) {
2124   - if (rcu_cpu_has_callbacks(cpu))
2125   - mod_timer(&per_cpu(rcu_idle_gp_timer, cpu),
2126   - per_cpu(rcu_idle_gp_timer_expires, cpu));
  2126 + if (rcu_cpu_has_callbacks(cpu)) {
  2127 + tp = &per_cpu(rcu_idle_gp_timer, cpu);
  2128 + mod_timer_pinned(tp, per_cpu(rcu_idle_gp_timer_expires, cpu));
  2129 + }
2127 2130 return;
2128 2131 }
2129 2132 per_cpu(rcu_idle_first_pass, cpu) = 0;
... ... @@ -2167,8 +2170,8 @@
2167 2170 else
2168 2171 per_cpu(rcu_idle_gp_timer_expires, cpu) =
2169 2172 jiffies + RCU_IDLE_LAZY_GP_DELAY;
2170   - mod_timer(&per_cpu(rcu_idle_gp_timer, cpu),
2171   - per_cpu(rcu_idle_gp_timer_expires, cpu));
  2173 + tp = &per_cpu(rcu_idle_gp_timer, cpu);
  2174 + mod_timer_pinned(tp, per_cpu(rcu_idle_gp_timer_expires, cpu));
2172 2175 per_cpu(rcu_nonlazy_posted_snap, cpu) =
2173 2176 per_cpu(rcu_nonlazy_posted, cpu);
2174 2177 return; /* Nothing more to do immediately. */