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rcu: Once again use NMI-based stack traces in stall warnings

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This commit is for all intents and purposes a revert of bc1dce514e
("rcu: Don't use NMIs to dump other CPUs' stacks").  The reason to suppose
that this can now safely be reverted is the presence of 42a0bb3f71
("printk/nmi: generic solution for safe printk in NMI"), which is said
to have made NMI-based stack dumps safe.

However, this reversion keeps one nice property of bc1dce514e
("rcu: Don't use NMIs to dump other CPUs' stacks"), namely that
only those CPUs blocking the grace period are dumped.  The new
trigger_single_cpu_backtrace() is used to make this happen, as
suggested by Josh Poimboeuf.

Reported-by: Vince Weaver <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Reviewed-by: Josh Poimboeuf <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Reviewed-by: Josh Triplett <[email protected]>
This commit is contained in:
Paul E. McKenney 2016-11-29 05:49:06 -08:00
commit 7aa92230c9
1 changed files with 7 additions and 5 deletions
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12
kernel/rcu/tree.c
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@ -1278,7 +1278,10 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
}
/*
* Dump stacks of all tasks running on stalled CPUs.
* Dump stacks of all tasks running on stalled CPUs. First try using
* NMIs, but fall back to manual remote stack tracing on architectures
* that don't support NMI-based stack dumps. The NMI-triggered stack
* traces are more accurate because they are printed by the target CPU.
*/
static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
{
@ -1288,11 +1291,10 @@ static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
rcu_for_each_leaf_node(rsp, rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->qsmask != 0) {
for_each_leaf_node_possible_cpu(rnp, cpu)
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
for_each_leaf_node_possible_cpu(rnp, cpu)
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
if (!trigger_single_cpu_backtrace(cpu))
dump_cpu_task(cpu);
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}