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rcu: Mark accesses to rcu_state.n_force_qs 

This commit marks accesses to the rcu_state.n_force_qs.  These data
races are hard to make happen, but syzkaller was equal to the task.

Reported-by: syzbot+e08a83a1940ec3846cd5@syzkaller.appspotmail.com
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-07-20 06:16:27 -07:00
parent 6880fa6c56
commit 2431774f04
1 changed files with 5 additions and 5 deletions
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10
kernel/rcu/tree.c
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@ -1907,7 +1907,7 @@ static void rcu_gp_fqs(bool first_time)
struct rcu_node *rnp = rcu_get_root();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
rcu_state.n_force_qs++;
WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
if (first_time) {
/* Collect dyntick-idle snapshots. */
force_qs_rnp(dyntick_save_progress_counter);
@ -2550,7 +2550,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
if (count == 0 && rdp->qlen_last_fqs_check != 0) {
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rcu_state.n_force_qs;
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
} else if (count < rdp->qlen_last_fqs_check - qhimark)
rdp->qlen_last_fqs_check = count;
@ -2898,10 +2898,10 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
} else {
/* Give the grace period a kick. */
rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&
if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
rcu_force_quiescent_state();
rdp->n_force_qs_snap = rcu_state.n_force_qs;
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
}
}
@ -4128,7 +4128,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rcu_state.n_force_qs;
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
rdp->blimit = blimit;
rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
rcu_dynticks_eqs_online();