diff options
Diffstat (limited to 'kernel/rcu/tree_stall.h')
| -rw-r--r-- | kernel/rcu/tree_stall.h | 40 |
1 files changed, 36 insertions, 4 deletions
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 119ed6afd20f..4dede00e2936 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -15,10 +15,12 @@ int sysctl_panic_on_rcu_stall __read_mostly; #ifdef CONFIG_PROVE_RCU -#define RCU_STALL_DELAY_DELTA (5 * HZ) +#define RCU_STALL_DELAY_DELTA (5 * HZ) #else -#define RCU_STALL_DELAY_DELTA 0 +#define RCU_STALL_DELAY_DELTA 0 #endif +#define RCU_STALL_MIGHT_DIV 8 +#define RCU_STALL_MIGHT_MIN (2 * HZ) /* Limit-check stall timeouts specified at boottime and runtime. */ int rcu_jiffies_till_stall_check(void) @@ -40,6 +42,36 @@ int rcu_jiffies_till_stall_check(void) } EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check); +/** + * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled? + * + * Returns @true if the current grace period is sufficiently old that + * it is reasonable to assume that it might be stalled. This can be + * useful when deciding whether to allocate memory to enable RCU-mediated + * freeing on the one hand or just invoking synchronize_rcu() on the other. + * The latter is preferable when the grace period is stalled. + * + * Note that sampling of the .gp_start and .gp_seq fields must be done + * carefully to avoid false positives at the beginnings and ends of + * grace periods. + */ +bool rcu_gp_might_be_stalled(void) +{ + unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV; + unsigned long j = jiffies; + + if (d < RCU_STALL_MIGHT_MIN) + d = RCU_STALL_MIGHT_MIN; + smp_mb(); // jiffies before .gp_seq to avoid false positives. + if (!rcu_gp_in_progress()) + return false; + // Long delays at this point avoids false positive, but a delay + // of ULONG_MAX/4 jiffies voids your no-false-positive warranty. + smp_mb(); // .gp_seq before second .gp_start + // And ditto here. + return !time_before(j, READ_ONCE(rcu_state.gp_start) + d); +} + /* Don't do RCU CPU stall warnings during long sysrq printouts. */ void rcu_sysrq_start(void) { @@ -104,8 +136,8 @@ static void record_gp_stall_check_time(void) WRITE_ONCE(rcu_state.gp_start, j); j1 = rcu_jiffies_till_stall_check(); - /* Record ->gp_start before ->jiffies_stall. */ - smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */ + smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq. + WRITE_ONCE(rcu_state.jiffies_stall, j + j1); rcu_state.jiffies_resched = j + j1 / 2; rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs); } |