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Commit bc1dce51 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Don't use NMIs to dump other CPUs' stacks 



Although NMI-based stack dumps are in principle more accurate, they are
also more likely to trigger deadlocks.  This commit therefore replaces
all uses of trigger_all_cpu_backtrace() with rcu_dump_cpu_stacks(), so
that the CPU detecting an RCU CPU stall does the stack dumping.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
parent c0f489d2

kernel/rcu/tree.c

+3 −7
Original line number Diff line number Diff line
@@ -1013,10 +1013,7 @@ static void record_gp_stall_check_time(struct rcu_state *rsp) 
}



/*

 * Dump stacks of all tasks running on stalled CPUs.  This is a fallback

 * for architectures that do not implement trigger_all_cpu_backtrace().

 * The NMI-triggered stack traces are more accurate because they are

 * printed by the target CPU.

 * Dump stacks of all tasks running on stalled CPUs.

 */

static void rcu_dump_cpu_stacks(struct rcu_state *rsp)

{
@@ -1094,7 +1091,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp) 
	       (long)rsp->gpnum, (long)rsp->completed, totqlen);

	if (ndetected == 0)

		pr_err("INFO: Stall ended before state dump start\n");

	else if (!trigger_all_cpu_backtrace())

	else

		rcu_dump_cpu_stacks(rsp);



	/* Complain about tasks blocking the grace period. */
@@ -1125,8 +1122,7 @@ static void print_cpu_stall(struct rcu_state *rsp) 
	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",

		jiffies - rsp->gp_start,

		(long)rsp->gpnum, (long)rsp->completed, totqlen);

	if (!trigger_all_cpu_backtrace())

		dump_stack();

	rcu_dump_cpu_stacks(rsp);



	raw_spin_lock_irqsave(&rnp->lock, flags);

	if (ULONG_CMP_GE(jiffies, ACCESS_ONCE(rsp->jiffies_stall)))