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rcu: Summarize RCU CPU stall warnings during CSD-lock stalls

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During CSD-lock stalls, the additional information output by RCU CPU
stall warnings is usually redundant, flooding the console for not good
reason.  However, this has been the way things work for a few years.
This commit therefore adds an rcutree.csd_lock_suppress_rcu_stall kernel
boot parameter that causes RCU CPU stall warnings to be abbreviated to
a single line when there is at least one CPU that has been stuck waiting
for CSD lock for more than five seconds.

To make this abbreviated message happen with decent probability:

tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 8 \
	--configs "2*TREE01" --kconfig "CONFIG_CSD_LOCK_WAIT_DEBUG=y" \
	--bootargs "csdlock_debug=1 rcutorture.stall_cpu=200 \
	rcutorture.stall_cpu_holdoff=120 rcutorture.stall_cpu_irqsoff=1 \
	rcutree.csd_lock_suppress_rcu_stall=1 \
	rcupdate.rcu_exp_cpu_stall_timeout=5000" --trust-make

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
This commit is contained in:
Paul E. McKenney 2024-07-01 19:30:56 -07:00 committed by Neeraj Upadhyay
parent 9fbaa44114
commit 1dd01c0650
2 changed files with 11 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
Documentation/admin-guide/kernel-parameters.txt
View File

@ -4937,6 +4937,10 @@
Set maximum number of finished RCU callbacks to
process in one batch.
rcutree.csd_lock_suppress_rcu_stall= [KNL]
Do only a one-line RCU CPU stall warning when
there is an ongoing too-long CSD-lock wait.
rcutree.do_rcu_barrier= [KNL]
Request a call to rcu_barrier(). This is
throttled so that userspace tests can safely

8
kernel/rcu/tree_stall.h
View File

@ -9,6 +9,7 @@
#include <linux/kvm_para.h>
#include <linux/rcu_notifier.h>
#include <linux/smp.h>
//////////////////////////////////////////////////////////////////////////////
//
@ -719,6 +720,9 @@ static void print_cpu_stall(unsigned long gps)
set_preempt_need_resched();
}
static bool csd_lock_suppress_rcu_stall;
module_param(csd_lock_suppress_rcu_stall, bool, 0644);
static void check_cpu_stall(struct rcu_data *rdp)
{
bool self_detected;
@ -791,7 +795,9 @@ static void check_cpu_stall(struct rcu_data *rdp)
return;
rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_NORM, (void *)j - gps);
if (self_detected) {
if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) {
pr_err("INFO: %s detected stall, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name);
} else if (self_detected) {
/* We haven't checked in, so go dump stack. */
print_cpu_stall(gps);
} else {