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Date: Wed, 17 Feb 2010 16:30:39 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
dipankar@...ibm.com, akpm@...ux-foundation.org,
josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [PATCH tip/core/rcu 17/18] rcu: stop overflowing signed
integers
* Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> 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.
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
I had to do something similar for liburcu QSBR to follow the standard.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.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
>
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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