* [PATCH] hrtimer: annotate lockless access to timer->base
@ 2019-10-08 17:32 Eric Dumazet
2019-10-14 4:10 ` Eric Dumazet
2019-10-14 13:58 ` [tip: timers/urgent] hrtimer: Annotate " tip-bot2 for Eric Dumazet
0 siblings, 2 replies; 3+ messages in thread
From: Eric Dumazet @ 2019-10-08 17:32 UTC (permalink / raw)
To: Thomas Gleixner; +Cc: linux-kernel, Eric Dumazet, Eric Dumazet, Julien Grall
Followup to commit dd2261ed45aa ("hrtimer: Protect lockless access
to timer->base")
lock_hrtimer_base() fetches timer->base without lock exclusion.
Compiler is allowed to read timer->base twice (even if considered dumb)
and we could end up trying to lock migration_base and
return &migration_base.
base = timer->base;
if (likely(base != &migration_base)) {
/* compiler reads timer->base again, and now (base == &migration_base)
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
return base; /* == &migration_base ! */
Similarly the write sides should use WRITE_ONCE() to avoid
store tearing.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Julien Grall <julien.grall@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/hrtimer.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0d4dc241c0fb498036c91a571e65cb00f5d19ba6..65605530ee349c9682690c4fccb43aa9284d4287 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -164,7 +164,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
struct hrtimer_clock_base *base;
for (;;) {
- base = timer->base;
+ base = READ_ONCE(timer->base);
if (likely(base != &migration_base)) {
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
@@ -244,7 +244,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
return base;
/* See the comment in lock_hrtimer_base() */
- timer->base = &migration_base;
+ WRITE_ONCE(timer->base, &migration_base);
raw_spin_unlock(&base->cpu_base->lock);
raw_spin_lock(&new_base->cpu_base->lock);
@@ -253,10 +253,10 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
raw_spin_unlock(&new_base->cpu_base->lock);
raw_spin_lock(&base->cpu_base->lock);
new_cpu_base = this_cpu_base;
- timer->base = base;
+ WRITE_ONCE(timer->base, base);
goto again;
}
- timer->base = new_base;
+ WRITE_ONCE(timer->base, new_base);
} else {
if (new_cpu_base != this_cpu_base &&
hrtimer_check_target(timer, new_base)) {
--
2.23.0.581.g78d2f28ef7-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] hrtimer: annotate lockless access to timer->base
2019-10-08 17:32 [PATCH] hrtimer: annotate lockless access to timer->base Eric Dumazet
@ 2019-10-14 4:10 ` Eric Dumazet
2019-10-14 13:58 ` [tip: timers/urgent] hrtimer: Annotate " tip-bot2 for Eric Dumazet
1 sibling, 0 replies; 3+ messages in thread
From: Eric Dumazet @ 2019-10-14 4:10 UTC (permalink / raw)
To: Thomas Gleixner; +Cc: linux-kernel, Eric Dumazet, Julien Grall
On Tue, Oct 8, 2019 at 10:32 AM Eric Dumazet <edumazet@google.com> wrote:
>
> Followup to commit dd2261ed45aa ("hrtimer: Protect lockless access
> to timer->base")
>
> lock_hrtimer_base() fetches timer->base without lock exclusion.
>
> Compiler is allowed to read timer->base twice (even if considered dumb)
> and we could end up trying to lock migration_base and
> return &migration_base.
>
> base = timer->base;
> if (likely(base != &migration_base)) {
>
> /* compiler reads timer->base again, and now (base == &migration_base)
>
> raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
> if (likely(base == timer->base))
> return base; /* == &migration_base ! */
>
> Similarly the write sides should use WRITE_ONCE() to avoid
> store tearing.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Julien Grall <julien.grall@arm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---
> kernel/time/hrtimer.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 0d4dc241c0fb498036c91a571e65cb00f5d19ba6..65605530ee349c9682690c4fccb43aa9284d4287 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -164,7 +164,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
> struct hrtimer_clock_base *base;
>
> for (;;) {
> - base = timer->base;
> + base = READ_ONCE(timer->base);
> if (likely(base != &migration_base)) {
> raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
> if (likely(base == timer->base))
> @@ -244,7 +244,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
> return base;
>
> /* See the comment in lock_hrtimer_base() */
> - timer->base = &migration_base;
> + WRITE_ONCE(timer->base, &migration_base);
> raw_spin_unlock(&base->cpu_base->lock);
> raw_spin_lock(&new_base->cpu_base->lock);
>
> @@ -253,10 +253,10 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
> raw_spin_unlock(&new_base->cpu_base->lock);
> raw_spin_lock(&base->cpu_base->lock);
> new_cpu_base = this_cpu_base;
> - timer->base = base;
> + WRITE_ONCE(timer->base, base);
> goto again;
> }
> - timer->base = new_base;
> + WRITE_ONCE(timer->base, new_base);
> } else {
> if (new_cpu_base != this_cpu_base &&
> hrtimer_check_target(timer, new_base)) {
> --
> 2.23.0.581.g78d2f28ef7-goog
>
Any news on this patch ?
If more information is needed, let me know.
Maybe I need to point to :
commit b831275a3553c32091222ac619cfddd73a5553fb timers: Plug locking
race vs. timer migration
Thanks
^ permalink raw reply [flat|nested] 3+ messages in thread
* [tip: timers/urgent] hrtimer: Annotate lockless access to timer->base
2019-10-08 17:32 [PATCH] hrtimer: annotate lockless access to timer->base Eric Dumazet
2019-10-14 4:10 ` Eric Dumazet
@ 2019-10-14 13:58 ` tip-bot2 for Eric Dumazet
1 sibling, 0 replies; 3+ messages in thread
From: tip-bot2 for Eric Dumazet @ 2019-10-14 13:58 UTC (permalink / raw)
To: linux-tip-commits
Cc: Eric Dumazet, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
linux-kernel
The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: ff229eee3d897f52bd001c841f2d3cce8853ecdc
Gitweb: https://git.kernel.org/tip/ff229eee3d897f52bd001c841f2d3cce8853ecdc
Author: Eric Dumazet <edumazet@google.com>
AuthorDate: Tue, 08 Oct 2019 10:32:04 -07:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 14 Oct 2019 15:51:49 +02:00
hrtimer: Annotate lockless access to timer->base
Followup to commit dd2261ed45aa ("hrtimer: Protect lockless access
to timer->base")
lock_hrtimer_base() fetches timer->base without lock exclusion.
Compiler is allowed to read timer->base twice (even if considered dumb)
which could end up trying to lock migration_base and return
&migration_base.
base = timer->base;
if (likely(base != &migration_base)) {
/* compiler reads timer->base again, and now (base == &migration_base)
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
return base; /* == &migration_base ! */
Similarly the write sides must use WRITE_ONCE() to avoid store tearing.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191008173204.180879-1-edumazet@google.com
---
kernel/time/hrtimer.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0d4dc24..6560553 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -164,7 +164,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
struct hrtimer_clock_base *base;
for (;;) {
- base = timer->base;
+ base = READ_ONCE(timer->base);
if (likely(base != &migration_base)) {
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
@@ -244,7 +244,7 @@ again:
return base;
/* See the comment in lock_hrtimer_base() */
- timer->base = &migration_base;
+ WRITE_ONCE(timer->base, &migration_base);
raw_spin_unlock(&base->cpu_base->lock);
raw_spin_lock(&new_base->cpu_base->lock);
@@ -253,10 +253,10 @@ again:
raw_spin_unlock(&new_base->cpu_base->lock);
raw_spin_lock(&base->cpu_base->lock);
new_cpu_base = this_cpu_base;
- timer->base = base;
+ WRITE_ONCE(timer->base, base);
goto again;
}
- timer->base = new_base;
+ WRITE_ONCE(timer->base, new_base);
} else {
if (new_cpu_base != this_cpu_base &&
hrtimer_check_target(timer, new_base)) {
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2019-10-08 17:32 [PATCH] hrtimer: annotate lockless access to timer->base Eric Dumazet
2019-10-14 4:10 ` Eric Dumazet
2019-10-14 13:58 ` [tip: timers/urgent] hrtimer: Annotate " tip-bot2 for Eric Dumazet
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