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| author | Paul E. McKenney <paul.mckenney@linaro.org> | 2012-03-15 20:16:26 +0100 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-05-01 17:22:50 +0200 |
| commit | f511fc624642f0bb8cf65aaa28979737514d4746 (patch) | |
| tree | db1395c5d33da33c8ea6c82f6e5b7346cc5beb91 | |
| parent | rcu: Add warning for RCU_FAST_NO_HZ timer firing (diff) | |
| download | linux-f511fc624642f0bb8cf65aaa28979737514d4746.tar.xz linux-f511fc624642f0bb8cf65aaa28979737514d4746.zip | |
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>
| -rw-r--r-- | kernel/rcutree_plugin.h | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index ad61da79b311..d01e26df55a1 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2110,6 +2110,8 @@ static void rcu_cleanup_after_idle(int cpu) */ static void rcu_prepare_for_idle(int cpu) { + struct timer_list *tp; + /* * If this is an idle re-entry, for example, due to use of * RCU_NONIDLE() or the new idle-loop tracing API within the idle @@ -2121,9 +2123,10 @@ static void rcu_prepare_for_idle(int cpu) if (!per_cpu(rcu_idle_first_pass, cpu) && (per_cpu(rcu_nonlazy_posted, cpu) == per_cpu(rcu_nonlazy_posted_snap, cpu))) { - if (rcu_cpu_has_callbacks(cpu)) - mod_timer(&per_cpu(rcu_idle_gp_timer, cpu), - per_cpu(rcu_idle_gp_timer_expires, cpu)); + if (rcu_cpu_has_callbacks(cpu)) { + tp = &per_cpu(rcu_idle_gp_timer, cpu); + mod_timer_pinned(tp, per_cpu(rcu_idle_gp_timer_expires, cpu)); + } return; } per_cpu(rcu_idle_first_pass, cpu) = 0; @@ -2167,8 +2170,8 @@ static void rcu_prepare_for_idle(int cpu) else per_cpu(rcu_idle_gp_timer_expires, cpu) = jiffies + RCU_IDLE_LAZY_GP_DELAY; - mod_timer(&per_cpu(rcu_idle_gp_timer, cpu), - per_cpu(rcu_idle_gp_timer_expires, cpu)); + tp = &per_cpu(rcu_idle_gp_timer, cpu); + mod_timer_pinned(tp, per_cpu(rcu_idle_gp_timer_expires, cpu)); per_cpu(rcu_nonlazy_posted_snap, cpu) = per_cpu(rcu_nonlazy_posted, cpu); return; /* Nothing more to do immediately. */ |