rcu: Set a maximum limit for back-to-back callback invocation

mainline inclusion
from mainline-v5.3-rc1
commit d5a9a8c3
category: bugfix
bugzilla: 187356, https://gitee.com/openeuler/kernel/issues/I5KOZ5
CVE: NA

---------------------------

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: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NPaul E. McKenney <paulmck@linux.ibm.com>
Conflicts:
	kernel/rcu/tree.c
Signed-off-by: NZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: NCheng Jian <cj.chengjian@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

kernel/rcu/tree.c

@@ -490,7 +490,8 @@ void rcu_all_qs(void)
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
 
-#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;
@@ -2604,7 +2605,7 @@ static void rcu_do_batch(struct rcu_state *rsp, 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. */
@@ -2940,7 +2941,7 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 			rcu_accelerate_cbs_unlocked(rsp, rdp->mynode, rdp);
 		} else {
 			/* Give the grace period a kick. */
-			rdp->blimit = LONG_MAX;
+			rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
 			if (rsp->n_force_qs == rdp->n_force_qs_snap &&
 			    rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
 				force_quiescent_state(rsp);