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rcu/nocb: Perform deferred wake up before last idle's need_resched() check

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commit 43789ef3f7d61aa7bed0cb2764e588fc990c30ef upstream.

Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
kthread (rcuog) to be serviced.

Usually a local wake up happening while running the idle task is handled
in one of the need_resched() checks carefully placed within the idle
loop that can break to the scheduler.

Unfortunately the call to rcu_idle_enter() is already beyond the last
generic need_resched() check and we may halt the CPU with a resched
request unhandled, leaving the task hanging.

Fix this with splitting the rcuog wakeup handling from rcu_idle_enter()
and place it before the last generic need_resched() check in the idle
loop. It is then assumed that no call to call_rcu() will be performed
after that in the idle loop until the CPU is put in low power mode.

Fixes: 96d3fd0d31 (rcu: Break call_rcu() deadlock involving scheduler and perf)
Reported-by: Paul E. McKenney <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Frederic Weisbecker 2021-02-01 00:05:45 +01:00 • committed by Greg Kroah-Hartman
commit 337bba09d8
4 changed files with 8 additions and 3 deletions
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3
kernel/rcu/tree.c
View file

@ -599,10 +599,7 @@ static void rcu_eqs_enter(bool user)
*/
void rcu_idle_enter(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
lockdep_assert_irqs_disabled();
do_nocb_deferred_wakeup(rdp);
rcu_eqs_enter(false);
}

5
kernel/rcu/tree_plugin.h
View file

@ -2190,6 +2190,11 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
do_nocb_deferred_wakeup_common(rdp);
}
void rcu_nocb_flush_deferred_wakeup(void)
{
do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
}
void __init rcu_init_nohz(void)
{
int cpu;