From b169246feb1d82dbee5f3f6a4ce57368644dce95 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 21 May 2021 14:23:03 -0700 Subject: [PATCH] rcu: Start timing stall repetitions after warning complete Systems with low-bandwidth consoles can have very large printk() latencies, and on such systems it makes no sense to have the next RCU CPU stall warning message start output before the prior message completed. This commit therefore sets the time of the next stall only after the prints have completed. While printing, the time of the next stall message is set to ULONG_MAX/2 jiffies into the future. Reviewed-by: Sergey Senozhatsky Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_stall.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index e199022d..42847ca 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -647,6 +647,7 @@ static void print_cpu_stall(unsigned long gps) static void check_cpu_stall(struct rcu_data *rdp) { + bool didstall = false; unsigned long gs1; unsigned long gs2; unsigned long gps; @@ -692,7 +693,7 @@ static void check_cpu_stall(struct rcu_data *rdp) ULONG_CMP_GE(gps, js)) return; /* No stall or GP completed since entering function. */ rnp = rdp->mynode; - jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; + jn = jiffies + ULONG_MAX / 2; if (rcu_gp_in_progress() && (READ_ONCE(rnp->qsmask) & rdp->grpmask) && cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { @@ -709,6 +710,7 @@ static void check_cpu_stall(struct rcu_data *rdp) print_cpu_stall(gps); if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) rcu_ftrace_dump(DUMP_ALL); + didstall = true; } else if (rcu_gp_in_progress() && ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) && @@ -726,6 +728,11 @@ static void check_cpu_stall(struct rcu_data *rdp) print_other_cpu_stall(gs2, gps); if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) rcu_ftrace_dump(DUMP_ALL); + didstall = true; + } + if (didstall && READ_ONCE(rcu_state.jiffies_stall) == jn) { + jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; + WRITE_ONCE(rcu_state.jiffies_stall, jn); } } -- 2.7.4