* [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
@ 2010-09-28 8:32 Dongdong Deng
2010-09-28 23:28 ` Paul E. McKenney
0 siblings, 1 reply; 4+ messages in thread
From: Dongdong Deng @ 2010-09-28 8:32 UTC (permalink / raw)
To: paulmck, dipankar; +Cc: linux-kernel, dongdong.deng
Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
due to the caller didn't hold the root_rcu/rnp node's lock.
Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
CC: Dipankar Sarma <dipankar@in.ibm.com>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d5bc439..07a7063 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -532,9 +532,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
if (rcu_cpu_stall_panicking)
return;
- delta = jiffies - rsp->jiffies_stall;
+ delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
rnp = rdp->mynode;
- if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
+ if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
/* We haven't checked in, so go dump stack. */
print_cpu_stall(rsp);
--
1.6.0.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
2010-09-28 8:32 [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value Dongdong Deng
@ 2010-09-28 23:28 ` Paul E. McKenney
2010-09-29 6:46 ` DDD
0 siblings, 1 reply; 4+ messages in thread
From: Paul E. McKenney @ 2010-09-28 23:28 UTC (permalink / raw)
To: Dongdong Deng; +Cc: dipankar, linux-kernel
On Tue, Sep 28, 2010 at 04:32:43PM +0800, Dongdong Deng wrote:
> Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
> due to the caller didn't hold the root_rcu/rnp node's lock.
Given that the quantities are only used once, ACCESS_ONCE() is strictly
speaking not necessary. I am tempted to queue your patch regardless
for the documentation benefits.
Or is this patch necessary to fix a failure that you have been seeing?
In any case, thank you for taking a look at RCU!
Thanx, Paul
> Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
> CC: Dipankar Sarma <dipankar@in.ibm.com>
> CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> kernel/rcutree.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index d5bc439..07a7063 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -532,9 +532,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
>
> if (rcu_cpu_stall_panicking)
> return;
> - delta = jiffies - rsp->jiffies_stall;
> + delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
> rnp = rdp->mynode;
> - if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
> + if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
>
> /* We haven't checked in, so go dump stack. */
> print_cpu_stall(rsp);
> --
> 1.6.0.4
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
2010-09-28 23:28 ` Paul E. McKenney
@ 2010-09-29 6:46 ` DDD
2010-10-07 0:43 ` Paul E. McKenney
0 siblings, 1 reply; 4+ messages in thread
From: DDD @ 2010-09-29 6:46 UTC (permalink / raw)
To: paulmck; +Cc: dipankar, linux-kernel
Paul E. McKenney wrote:
> On Tue, Sep 28, 2010 at 04:32:43PM +0800, Dongdong Deng wrote:
>> Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
>> due to the caller didn't hold the root_rcu/rnp node's lock.
>
> Given that the quantities are only used once, ACCESS_ONCE() is strictly
> speaking not necessary. I am tempted to queue your patch regardless
> for the documentation benefits.
>
> Or is this patch necessary to fix a failure that you have been seeing?
Hello Pual,
No, I didn't see a failure about it.
I got this patch from code review. :-)
Thanks,
Dongdong
> In any case, thank you for taking a look at RCU!
>
> Thanx, Paul
>
>> Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
>> CC: Dipankar Sarma <dipankar@in.ibm.com>
>> CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>> ---
>> kernel/rcutree.c | 4 ++--
>> 1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
>> index d5bc439..07a7063 100644
>> --- a/kernel/rcutree.c
>> +++ b/kernel/rcutree.c
>> @@ -532,9 +532,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
>>
>> if (rcu_cpu_stall_panicking)
>> return;
>> - delta = jiffies - rsp->jiffies_stall;
>> + delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
>> rnp = rdp->mynode;
>> - if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
>> + if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
>>
>> /* We haven't checked in, so go dump stack. */
>> print_cpu_stall(rsp);
>> --
>> 1.6.0.4
>>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
2010-09-29 6:46 ` DDD
@ 2010-10-07 0:43 ` Paul E. McKenney
0 siblings, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2010-10-07 0:43 UTC (permalink / raw)
To: DDD; +Cc: dipankar, linux-kernel
On Wed, Sep 29, 2010 at 02:46:18PM +0800, DDD wrote:
> Paul E. McKenney wrote:
> >On Tue, Sep 28, 2010 at 04:32:43PM +0800, Dongdong Deng wrote:
> >>Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
> >>due to the caller didn't hold the root_rcu/rnp node's lock.
> >
> >Given that the quantities are only used once, ACCESS_ONCE() is strictly
> >speaking not necessary. I am tempted to queue your patch regardless
> >for the documentation benefits.
> >
> >Or is this patch necessary to fix a failure that you have been seeing?
>
> Hello Pual,
>
> No, I didn't see a failure about it.
> I got this patch from code review. :-)
Thank you for the info, patch queued.
Thanx, Paul
> Thanks,
> Dongdong
>
> >In any case, thank you for taking a look at RCU!
> >
> > Thanx, Paul
> >
> >>Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
> >>CC: Dipankar Sarma <dipankar@in.ibm.com>
> >>CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> >>---
> >> kernel/rcutree.c | 4 ++--
> >> 1 files changed, 2 insertions(+), 2 deletions(-)
> >>
> >>diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> >>index d5bc439..07a7063 100644
> >>--- a/kernel/rcutree.c
> >>+++ b/kernel/rcutree.c
> >>@@ -532,9 +532,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
> >>
> >> if (rcu_cpu_stall_panicking)
> >> return;
> >>- delta = jiffies - rsp->jiffies_stall;
> >>+ delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
> >> rnp = rdp->mynode;
> >>- if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
> >>+ if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
> >>
> >> /* We haven't checked in, so go dump stack. */
> >> print_cpu_stall(rsp);
> >>--
> >>1.6.0.4
> >>
> >
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2010-09-28 8:32 [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value Dongdong Deng
2010-09-28 23:28 ` Paul E. McKenney
2010-09-29 6:46 ` DDD
2010-10-07 0:43 ` Paul E. McKenney
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