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Subject[PATCH tip/core/rcu 17/21] rcu: stop overflowing signed integers
Date
The C standard does not specify the result of an operation that overflows
a signed integer, so such operations need to be avoided. This patch
changes the type of several fields from "long" to "unsigned long" and
adjusts operations as needed. ULONG_CMP_GE() and ULONG_CMP_LT() macros
are introduced to do the modular comparisons that are appropriate given
that overflow is an expected event.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 11 +++++------
kernel/rcutree.h | 33 ++++++++++++++++++---------------
kernel/rcutree_trace.c | 14 +++++++-------
3 files changed, 30 insertions(+), 28 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 29d88c0..dd0d31d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -500,7 +500,7 @@ static void print_cpu_stall(struct rcu_state *rsp)
trigger_all_cpu_backtrace();

spin_lock_irqsave(&rnp->lock, flags);
- if ((long)(jiffies - rsp->jiffies_stall) >= 0)
+ if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
rsp->jiffies_stall =
jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
spin_unlock_irqrestore(&rnp->lock, flags);
@@ -1216,8 +1216,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
return; /* Someone else is already on the job. */
}
- if (relaxed &&
- (long)(rsp->jiffies_force_qs - jiffies) >= 0)
+ if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
goto unlock_fqs_ret; /* no emergency and done recently. */
rsp->n_force_qs++;
spin_lock(&rnp->lock); /* irqs already disabled */
@@ -1295,7 +1294,7 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
* If an RCU GP has gone long enough, go check for dyntick
* idle CPUs and, if needed, send resched IPIs.
*/
- if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
+ if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
force_quiescent_state(rsp, 1);

/*
@@ -1392,7 +1391,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
force_quiescent_state(rsp, 0);
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->qlen_last_fqs_check = rdp->qlen;
- } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
+ } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
force_quiescent_state(rsp, 1);
local_irq_restore(flags);
}
@@ -1525,7 +1524,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)

/* Has an RCU GP gone long enough to send resched IPIs &c? */
if (rcu_gp_in_progress(rsp) &&
- ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
+ ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
rdp->n_rp_need_fqs++;
return 1;
}
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index d9d032a..7495fed 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -92,10 +92,10 @@ struct rcu_dynticks {
struct rcu_node {
spinlock_t lock; /* Root rcu_node's lock protects some */
/* rcu_state fields as well as following. */
- long gpnum; /* Current grace period for this node. */
+ unsigned long gpnum; /* Current grace period for this node. */
/* This will either be equal to or one */
/* behind the root rcu_node's gpnum. */
- long completed; /* Last grace period completed for this node. */
+ unsigned long completed; /* Last GP completed for this node. */
/* This will either be equal to or one */
/* behind the root rcu_node's gpnum. */
unsigned long qsmask; /* CPUs or groups that need to switch in */
@@ -161,11 +161,11 @@ struct rcu_node {
/* Per-CPU data for read-copy update. */
struct rcu_data {
/* 1) quiescent-state and grace-period handling : */
- long completed; /* Track rsp->completed gp number */
+ unsigned long completed; /* Track rsp->completed gp number */
/* in order to detect GP end. */
- long gpnum; /* Highest gp number that this CPU */
+ unsigned long gpnum; /* Highest gp number that this CPU */
/* is aware of having started. */
- long passed_quiesc_completed;
+ unsigned long passed_quiesc_completed;
/* Value of completed at time of qs. */
bool passed_quiesc; /* User-mode/idle loop etc. */
bool qs_pending; /* Core waits for quiesc state. */
@@ -221,14 +221,14 @@ struct rcu_data {
unsigned long resched_ipi; /* Sent a resched IPI. */

/* 5) __rcu_pending() statistics. */
- long n_rcu_pending; /* rcu_pending() calls since boot. */
- long n_rp_qs_pending;
- long n_rp_cb_ready;
- long n_rp_cpu_needs_gp;
- long n_rp_gp_completed;
- long n_rp_gp_started;
- long n_rp_need_fqs;
- long n_rp_need_nothing;
+ unsigned long n_rcu_pending; /* rcu_pending() calls since boot. */
+ unsigned long n_rp_qs_pending;
+ unsigned long n_rp_cb_ready;
+ unsigned long n_rp_cpu_needs_gp;
+ unsigned long n_rp_gp_completed;
+ unsigned long n_rp_gp_started;
+ unsigned long n_rp_need_fqs;
+ unsigned long n_rp_need_nothing;

int cpu;
};
@@ -255,6 +255,9 @@ struct rcu_data {

#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */

+#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
+#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
+
/*
* RCU global state, including node hierarchy. This hierarchy is
* represented in "heap" form in a dense array. The root (first level)
@@ -283,8 +286,8 @@ struct rcu_state {
/* period because */
/* force_quiescent_state() */
/* was running. */
- long gpnum; /* Current gp number. */
- long completed; /* # of last completed gp. */
+ unsigned long gpnum; /* Current gp number. */
+ unsigned long completed; /* # of last completed gp. */

/* End of fields guarded by root rcu_node's lock. */

diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 9d2c884..d45db2e 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -50,7 +50,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
return;
- seq_printf(m, "%3d%cc=%ld g=%ld pq=%d pqc=%ld qp=%d",
+ seq_printf(m, "%3d%cc=%lu g=%lu pq=%d pqc=%lu qp=%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? '!' : ' ',
rdp->completed, rdp->gpnum,
@@ -105,7 +105,7 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
return;
- seq_printf(m, "%d,%s,%ld,%ld,%d,%ld,%d",
+ seq_printf(m, "%d,%s,%lu,%lu,%d,%lu,%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? "\"N\"" : "\"Y\"",
rdp->completed, rdp->gpnum,
@@ -155,13 +155,13 @@ static const struct file_operations rcudata_csv_fops = {

static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
{
- long gpnum;
+ unsigned long gpnum;
int level = 0;
int phase;
struct rcu_node *rnp;

gpnum = rsp->gpnum;
- seq_printf(m, "c=%ld g=%ld s=%d jfq=%ld j=%x "
+ seq_printf(m, "c=%lu g=%lu s=%d jfq=%ld j=%x "
"nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld\n",
rsp->completed, gpnum, rsp->signaled,
(long)(rsp->jiffies_force_qs - jiffies),
@@ -215,12 +215,12 @@ static const struct file_operations rcuhier_fops = {
static int show_rcugp(struct seq_file *m, void *unused)
{
#ifdef CONFIG_TREE_PREEMPT_RCU
- seq_printf(m, "rcu_preempt: completed=%ld gpnum=%ld\n",
+ seq_printf(m, "rcu_preempt: completed=%ld gpnum=%lu\n",
rcu_preempt_state.completed, rcu_preempt_state.gpnum);
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
- seq_printf(m, "rcu_sched: completed=%ld gpnum=%ld\n",
+ seq_printf(m, "rcu_sched: completed=%ld gpnum=%lu\n",
rcu_sched_state.completed, rcu_sched_state.gpnum);
- seq_printf(m, "rcu_bh: completed=%ld gpnum=%ld\n",
+ seq_printf(m, "rcu_bh: completed=%ld gpnum=%lu\n",
rcu_bh_state.completed, rcu_bh_state.gpnum);
return 0;
}
--
1.6.6


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