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rcu: Fix existing exp request check in sync_sched_exp_online_cleanup() 

[ Upstream commit f0b2b2df54 ]

The sync_sched_exp_online_cleanup() checks to see if RCU needs
an expedited quiescent state from the incoming CPU, sending it
an IPI if so. Before sending IPI, it checks whether expedited
qs need has been already requested for the incoming CPU, by
checking rcu_data.cpu_no_qs.b.exp for the current cpu, on which
sync_sched_exp_online_cleanup() is running. This works for the
case where incoming CPU is same as self. However, for the case
where incoming CPU is different from self, expedited request
won't get marked, which can potentially delay reporting of
expedited quiescent state for the incoming CPU.

Fixes: e015a34112 ("rcu: Avoid self-IPI in sync_sched_exp_online_cleanup()")
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Neeraj Upadhyay 2021-08-18 13:34:00 +05:30 committed by Greg Kroah-Hartman
parent 3998e06d95
commit 4a9334d04b
1 changed files with 1 additions and 1 deletions
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2
kernel/rcu/tree_exp.h
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@ -760,7 +760,7 @@ static void sync_sched_exp_online_cleanup(int cpu)
my_cpu = get_cpu();
/* Quiescent state either not needed or already requested, leave. */
if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) {
rdp->cpu_no_qs.b.exp) {
put_cpu();
return;
}