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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Conflicts:
	kernel/rcu/tree.c

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Cheng Jian <cj.chengjian@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>