From 5f3e9d9d3b7d558a59936f1826ff256d417ceac9 Mon Sep 17 00:00:00 2001 From: bill-auger Date: Sat, 16 Apr 2022 15:54:33 -0400 Subject: [linux-libre]: upgrade to v5.17.3 (x86_64 only) --- ...ick-rcu-Stop-allowing-RCU_SOFTIRQ-in-idle.patch | 119 +++++++++++++++++++++ 1 file changed, 119 insertions(+) create mode 100644 libre/linux-libre/0005-tick-rcu-Stop-allowing-RCU_SOFTIRQ-in-idle.patch (limited to 'libre/linux-libre/0005-tick-rcu-Stop-allowing-RCU_SOFTIRQ-in-idle.patch') diff --git a/libre/linux-libre/0005-tick-rcu-Stop-allowing-RCU_SOFTIRQ-in-idle.patch b/libre/linux-libre/0005-tick-rcu-Stop-allowing-RCU_SOFTIRQ-in-idle.patch new file mode 100644 index 000000000..0c3f3a6a4 --- /dev/null +++ b/libre/linux-libre/0005-tick-rcu-Stop-allowing-RCU_SOFTIRQ-in-idle.patch @@ -0,0 +1,119 @@ +From 894c674f70127b8fe02878ada383f534a1c63beb Mon Sep 17 00:00:00 2001 +From: Frederic Weisbecker +Date: Tue, 8 Feb 2022 17:16:34 +0100 +Subject: [PATCH 5/9] tick/rcu: Stop allowing RCU_SOFTIRQ in idle + +RCU_SOFTIRQ used to be special in that it could be raised on purpose +within the idle path to prevent from stopping the tick. Some code still +prevents from unnecessary warnings related to this specific behaviour +while entering in dynticks-idle mode. + +However the nohz layout has changed quite a bit in ten years, and the +removal of CONFIG_RCU_FAST_NO_HZ has been the final straw to this +safe-conduct. Now the RCU_SOFTIRQ vector is expected to be raised from +sane places. + +A remaining corner case is admitted though when the vector is invoked +in fragile hotplug path. + +Signed-off-by: Frederic Weisbecker +Cc: Thomas Gleixner +Cc: Peter Zijlstra +Cc: Paul E. McKenney +Cc: Paul Menzel +--- + include/linux/interrupt.h | 8 ++++++- + kernel/time/tick-sched.c | 50 +++++++++++++++++++++++++++++++-------- + 2 files changed, 47 insertions(+), 11 deletions(-) + +diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h +index 9367f1cb2e3c..9613326d2f8a 100644 +--- a/include/linux/interrupt.h ++++ b/include/linux/interrupt.h +@@ -579,7 +579,13 @@ enum + NR_SOFTIRQS + }; + +-#define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) ++/* ++ * Ignoring the RCU vector after ksoftirqd is parked is fine ++ * because: ++ * 1) rcutree_migrate_callbacks() takes care of the queue. ++ * 2) rcu_report_dead() reports the final quiescent states. ++ */ ++#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ)) + + /* map softirq index to softirq name. update 'softirq_to_name' in + * kernel/softirq.c when adding a new softirq. +diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c +index 566ad5bd83e9..2d76c91b85de 100644 +--- a/kernel/time/tick-sched.c ++++ b/kernel/time/tick-sched.c +@@ -999,6 +999,45 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts) + __tick_nohz_full_update_tick(ts, ktime_get()); + } + ++/* ++ * A pending softirq outside an IRQ (or softirq disabled section) context ++ * should be waiting for ksoftirqd to handle it. Therefore we shouldn't ++ * reach here due to the need_resched() early check in can_stop_idle_tick(). ++ * ++ * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the ++ * cpu_down() process, softirqs can still be raised while ksoftirqd is parked, ++ * triggering the below since wakep_softirqd() is ignored. ++ * ++ */ ++static bool report_idle_softirq(void) ++{ ++ static int ratelimit; ++ unsigned int pending = local_softirq_pending(); ++ ++ if (likely(!pending)) ++ return false; ++ ++ /* Some softirqs claim to be safe against hotplug and ksoftirqd parking */ ++ if (!cpu_active(smp_processor_id())) { ++ pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK; ++ if (!pending) ++ return false; ++ } ++ ++ if (ratelimit < 10) ++ return false; ++ ++ /* On RT, softirqs handling may be waiting on some lock */ ++ if (!local_bh_blocked()) ++ return false; ++ ++ pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n", ++ pending); ++ ratelimit++; ++ ++ return true; ++} ++ + static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) + { + /* +@@ -1025,17 +1064,8 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) + if (need_resched()) + return false; + +- if (unlikely(local_softirq_pending())) { +- static int ratelimit; +- +- if (ratelimit < 10 && !local_bh_blocked() && +- (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { +- pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n", +- (unsigned int) local_softirq_pending()); +- ratelimit++; +- } ++ if (unlikely(report_idle_softirq())) + return false; +- } + + if (tick_nohz_full_enabled()) { + /* +-- +2.35.1 + -- cgit v1.2.3