From d5a9a8c3bc8068f2e5dfba30150ac09b596b461a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 10 Apr 2019 17:01:39 -0700 Subject: rcu: Set a maximum limit for back-to-back callback invocation Currently, if a CPU has more than 10,000 callbacks pending, it will increase rdp->blimit to LONG_MAX. If you are lucky, LONG_MAX is only about two billion, but this is still a bit too many callbacks to invoke back-to-back while otherwise ignoring the world. This commit therefore sets a maximum limit of DEFAULT_MAX_RCU_BLIMIT, which is set to 10,000, for rdp->blimit. Reported-by: Sebastian Andrzej Siewior Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 980ca3ca643f..f888a76673da 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -380,7 +380,8 @@ static int rcu_is_cpu_rrupt_from_idle(void) __this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 1; } -#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch. */ +#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch ... */ +#define DEFAULT_MAX_RCU_BLIMIT 10000 /* ... even during callback flood. */ static long blimit = DEFAULT_RCU_BLIMIT; #define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */ static long qhimark = DEFAULT_RCU_QHIMARK; @@ -2113,7 +2114,7 @@ static void rcu_do_batch(struct rcu_data *rdp) /* Reinstate batch limit if we have worked down the excess. */ count = rcu_segcblist_n_cbs(&rdp->cblist); - if (rdp->blimit == LONG_MAX && count <= qlowmark) + if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark) rdp->blimit = blimit; /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ @@ -2354,7 +2355,7 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head, rcu_accelerate_cbs_unlocked(rdp->mynode, rdp); } else { /* Give the grace period a kick. */ - rdp->blimit = LONG_MAX; + rdp->blimit = DEFAULT_MAX_RCU_BLIMIT; if (rcu_state.n_force_qs == rdp->n_force_qs_snap && rcu_segcblist_first_pend_cb(&rdp->cblist) != head) rcu_force_quiescent_state(); -- cgit