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rcu: Avoid ->dynticks_nesting store tearing 

Although ->dynticks_nesting is updated only by process level, it is
accessed from hardirq to check for interrupt-from-idle quiescent states.
Store tearing is thus possible, so this commit applies WRITE_ONCE()
to ->dynticks_nesting stores.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-10-05 15:03:10 -07:00
parent 914955e18c
commit 2342172fd6
1 changed files with 3 additions and 3 deletions
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6
kernel/rcu/tree.c
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@ -778,7 +778,7 @@ static void rcu_eqs_enter_common(bool user)
do_nocb_deferred_wakeup(rdp); do_nocb_deferred_wakeup(rdp);
} }
rcu_prepare_for_idle(); rcu_prepare_for_idle();
rdtp->dynticks_nesting = 0; WRITE_ONCE(rdtp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
rcu_dynticks_eqs_enter(); rcu_dynticks_eqs_enter();
rcu_dynticks_task_enter(); rcu_dynticks_task_enter();
} }
@ -976,7 +976,7 @@ static void rcu_eqs_exit(bool user)
rdtp->dynticks_nesting++; rdtp->dynticks_nesting++;
} else { } else {
rcu_eqs_exit_common(1, user); rcu_eqs_exit_common(1, user);
rdtp->dynticks_nesting = 1; WRITE_ONCE(rdtp->dynticks_nesting, 1);
WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE); WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
} }
} }
@ -3713,7 +3713,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */ if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
!init_nocb_callback_list(rdp)) !init_nocb_callback_list(rdp))
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */ rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
rdp->dynticks->dynticks_nesting = 1; rdp->dynticks->dynticks_nesting = 1; /* CPU not up, no tearing. */
rcu_dynticks_eqs_online(); rcu_dynticks_eqs_online();
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */