* [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread_fun()
@ 2018-09-05 5:52 Neeraj Upadhyay
2018-09-05 8:12 ` Peter Zijlstra
2018-09-06 13:51 ` [tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() " tip-bot for Neeraj Upadhyay
0 siblings, 2 replies; 3+ messages in thread
From: Neeraj Upadhyay @ 2018-09-05 5:52 UTC (permalink / raw)
To: tglx, josh, peterz, mingo, jiangshanlai, dzickus,
brendan.jackman, malat, mojha
Cc: linux-kernel, sramana, linux-arm-msm, Neeraj Upadhyay
The smp_mb() in cpuhp_thread_fun() appears to be misplaced, and
need to be after the load of st->should_run, to prevent
reordering of the later load/stores w.r.t. the load of
st->should_run.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
---
kernel/cpu.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85..eb4041f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -607,15 +607,15 @@ static void cpuhp_thread_fun(unsigned int cpu)
bool bringup = st->bringup;
enum cpuhp_state state;
+ if (WARN_ON_ONCE(!st->should_run))
+ return;
+
/*
* ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
* that if we see ->should_run we also see the rest of the state.
*/
smp_mb();
- if (WARN_ON_ONCE(!st->should_run))
- return;
-
cpuhp_lock_acquire(bringup);
if (st->single) {
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread_fun()
2018-09-05 5:52 [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread_fun() Neeraj Upadhyay
@ 2018-09-05 8:12 ` Peter Zijlstra
2018-09-06 13:51 ` [tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() " tip-bot for Neeraj Upadhyay
1 sibling, 0 replies; 3+ messages in thread
From: Peter Zijlstra @ 2018-09-05 8:12 UTC (permalink / raw)
To: Neeraj Upadhyay
Cc: tglx, josh, mingo, jiangshanlai, dzickus, brendan.jackman, malat,
mojha, linux-kernel, sramana, linux-arm-msm
On Wed, Sep 05, 2018 at 11:22:07AM +0530, Neeraj Upadhyay wrote:
> The smp_mb() in cpuhp_thread_fun() appears to be misplaced, and
> need to be after the load of st->should_run, to prevent
> reordering of the later load/stores w.r.t. the load of
> st->should_run.
I'm tempted to say this changelog needs improvement, but given the
comment that goes with the smp_mb(), yes this is obviously right.
Acked-by: Peter Zijlstra (Intel) <peterz@infraded.org>
> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
> ---
> kernel/cpu.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index aa7fe85..eb4041f 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -607,15 +607,15 @@ static void cpuhp_thread_fun(unsigned int cpu)
> bool bringup = st->bringup;
> enum cpuhp_state state;
>
> + if (WARN_ON_ONCE(!st->should_run))
> + return;
> +
> /*
> * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
> * that if we see ->should_run we also see the rest of the state.
> */
> smp_mb();
>
> - if (WARN_ON_ONCE(!st->should_run))
> - return;
> -
> cpuhp_lock_acquire(bringup);
>
> if (st->single) {
^ permalink raw reply [flat|nested] 3+ messages in thread
* [tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() in cpuhp_thread_fun()
2018-09-05 5:52 [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread_fun() Neeraj Upadhyay
2018-09-05 8:12 ` Peter Zijlstra
@ 2018-09-06 13:51 ` tip-bot for Neeraj Upadhyay
1 sibling, 0 replies; 3+ messages in thread
From: tip-bot for Neeraj Upadhyay @ 2018-09-06 13:51 UTC (permalink / raw)
To: linux-tip-commits; +Cc: tglx, hpa, linux-kernel, peterz, mingo, neeraju
Commit-ID: f8b7530aa0a1def79c93101216b5b17cf408a70a
Gitweb: https://git.kernel.org/tip/f8b7530aa0a1def79c93101216b5b17cf408a70a
Author: Neeraj Upadhyay <neeraju@codeaurora.org>
AuthorDate: Wed, 5 Sep 2018 11:22:07 +0530
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 6 Sep 2018 15:21:37 +0200
cpu/hotplug: Adjust misplaced smb() in cpuhp_thread_fun()
The smp_mb() in cpuhp_thread_fun() is misplaced. It needs to be after the
load of st->should_run to prevent reordering of the later load/stores
w.r.t. the load of st->should_run.
Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infraded.org>
Cc: josh@joshtriplett.org
Cc: peterz@infradead.org
Cc: jiangshanlai@gmail.com
Cc: dzickus@redhat.com
Cc: brendan.jackman@arm.com
Cc: malat@debian.org
Cc: mojha@codeaurora.org
Cc: sramana@codeaurora.org
Cc: linux-arm-msm@vger.kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1536126727-11629-1-git-send-email-neeraju@codeaurora.org
---
kernel/cpu.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85ad62e..eb4041f78073 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -607,15 +607,15 @@ static void cpuhp_thread_fun(unsigned int cpu)
bool bringup = st->bringup;
enum cpuhp_state state;
+ if (WARN_ON_ONCE(!st->should_run))
+ return;
+
/*
* ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
* that if we see ->should_run we also see the rest of the state.
*/
smp_mb();
- if (WARN_ON_ONCE(!st->should_run))
- return;
-
cpuhp_lock_acquire(bringup);
if (st->single) {
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2018-09-05 5:52 [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread_fun() Neeraj Upadhyay
2018-09-05 8:12 ` Peter Zijlstra
2018-09-06 13:51 ` [tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() " tip-bot for Neeraj Upadhyay
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