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[PATCH v4] sched/psi: fix memory barrier without comment warnings

Pintu Kumar posted 1 patch 1 month, 3 weeks ago
There is a newer version of this series
kernel/sched/psi.c | 2 ++
1 file changed, 2 insertions(+)
[PATCH v4] sched/psi: fix memory barrier without comment warnings
Posted by Pintu Kumar 1 month, 3 weeks ago 
These warnings were reported by checkpatch.
Fix them with minor changes.
No functional changes.

WARNING: memory barrier without comment
+       t = smp_load_acquire(trigger_ptr);

WARNING: memory barrier without comment
+       smp_store_release(&seq->private, new);

Signed-off-by: Pintu Kumar <quic_pintu@quicinc.com>

---
Changes in V4:
Added () in comment as well suggested by Christophe JAILLET.
V3: https://lore.kernel.org/all/00aeb243-3d47-42be-b52c-08b39c5fef07@wanadoo.fr/
Changes in V3:
Removed signature of Joe as requested. No other change.
V2: https://lore.kernel.org/all/CAOuPNLi1mUKW_vv0E6Ynzvdw_rHvCye+nAf2bWv6Qj9A8ofX1g@mail.gmail.com/
Changes in V2:
Retain printk_deferred warnings as suggested by Joe Perches.
V1: https://lore.kernel.org/all/a848671f803ba2b4ab14b0f7b09f0f53a8dd1c4b.camel@perches.com/
---
 kernel/sched/psi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 020d58967d4e..175423716e4c 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1474,6 +1474,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr,
 	if (static_branch_likely(&psi_disabled))
 		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
 
+	/* Pairs with the smp_store_release() in psi_write */
 	t = smp_load_acquire(trigger_ptr);
 	if (!t)
 		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
@@ -1557,6 +1558,7 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
 		return PTR_ERR(new);
 	}
 
+	/* Pairs with the smp_store_acquire() in psi_trigger_poll */
 	smp_store_release(&seq->private, new);
 	mutex_unlock(&seq->lock);
 
-- 
2.17.1
Re: [PATCH v4] sched/psi: fix memory barrier without comment warnings
Posted by Christophe JAILLET 1 month, 3 weeks ago 
Le 06/10/2024 à 08:00, Pintu Kumar a écrit :
> These warnings were reported by checkpatch.
> Fix them with minor changes.
> No functional changes.
> 
> WARNING: memory barrier without comment
> +       t = smp_load_acquire(trigger_ptr);
> 
> WARNING: memory barrier without comment
> +       smp_store_release(&seq->private, new);
> 
> Signed-off-by: Pintu Kumar <quic_pintu@quicinc.com>
> 
> ---
> Changes in V4:
> Added () in comment as well suggested by Christophe JAILLET.
> V3: https://lore.kernel.org/all/00aeb243-3d47-42be-b52c-08b39c5fef07@wanadoo.fr/
> Changes in V3:
> Removed signature of Joe as requested. No other change.
> V2: https://lore.kernel.org/all/CAOuPNLi1mUKW_vv0E6Ynzvdw_rHvCye+nAf2bWv6Qj9A8ofX1g@mail.gmail.com/
> Changes in V2:
> Retain printk_deferred warnings as suggested by Joe Perches.
> V1: https://lore.kernel.org/all/a848671f803ba2b4ab14b0f7b09f0f53a8dd1c4b.camel@perches.com/
> ---
>   kernel/sched/psi.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 020d58967d4e..175423716e4c 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1474,6 +1474,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr,
>   	if (static_branch_likely(&psi_disabled))
>   		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
>   
> +	/* Pairs with the smp_store_release() in psi_write */
>   	t = smp_load_acquire(trigger_ptr);
>   	if (!t)
>   		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
> @@ -1557,6 +1558,7 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
>   		return PTR_ERR(new);
>   	}
>   
> +	/* Pairs with the smp_store_acquire() in psi_trigger_poll */

Sorry if I was unclear in my previous comment, but my main point is that 
I think that it should be smp_load_acquire() and not smp_store_acquire().

(Also, if you add some (), you could also add them for psi_trigger_poll 
and psi_write)

CJ

>   	smp_store_release(&seq->private, new);
>   	mutex_unlock(&seq->lock);
>
Re: [PATCH v4] sched/psi: fix memory barrier without comment warnings
Posted by Pintu Agarwal 1 month, 3 weeks ago 
On Sun, 6 Oct 2024 at 12:33, Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> Le 06/10/2024 à 08:00, Pintu Kumar a écrit :
> > These warnings were reported by checkpatch.
> > Fix them with minor changes.
> > No functional changes.
> >
> > WARNING: memory barrier without comment
> > +       t = smp_load_acquire(trigger_ptr);
> >
> > WARNING: memory barrier without comment
> > +       smp_store_release(&seq->private, new);
> >
> > Signed-off-by: Pintu Kumar <quic_pintu@quicinc.com>
> >
> > ---
> > Changes in V4:
> > Added () in comment as well suggested by Christophe JAILLET.
> > V3: https://lore.kernel.org/all/00aeb243-3d47-42be-b52c-08b39c5fef07@wanadoo.fr/
> > Changes in V3:
> > Removed signature of Joe as requested. No other change.
> > V2: https://lore.kernel.org/all/CAOuPNLi1mUKW_vv0E6Ynzvdw_rHvCye+nAf2bWv6Qj9A8ofX1g@mail.gmail.com/
> > Changes in V2:
> > Retain printk_deferred warnings as suggested by Joe Perches.
> > V1: https://lore.kernel.org/all/a848671f803ba2b4ab14b0f7b09f0f53a8dd1c4b.camel@perches.com/
> > ---
> >   kernel/sched/psi.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> > index 020d58967d4e..175423716e4c 100644
> > --- a/kernel/sched/psi.c
> > +++ b/kernel/sched/psi.c
> > @@ -1474,6 +1474,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr,
> >       if (static_branch_likely(&psi_disabled))
> >               return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
> >
> > +     /* Pairs with the smp_store_release() in psi_write */
> >       t = smp_load_acquire(trigger_ptr);
> >       if (!t)
> >               return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
> > @@ -1557,6 +1558,7 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
> >               return PTR_ERR(new);
> >       }
> >
> > +     /* Pairs with the smp_store_acquire() in psi_trigger_poll */
>
> Sorry if I was unclear in my previous comment, but my main point is that
> I think that it should be smp_load_acquire() and not smp_store_acquire().
>
> (Also, if you add some (), you could also add them for psi_trigger_poll
> and psi_write)
>
Oh sorry, my bad, I overlooked it again. You are right.
Thank you so much for pointing this out.
I corrected it now. Will push the new patchset again.
{{{
-       /* Pairs with the smp_store_release() in psi_write */
+       /* Pairs with the smp_store_release() in psi_write() */
        t = smp_load_acquire(trigger_ptr);
....
-       /* Pairs with the smp_store_acquire() in psi_trigger_poll */
+       /* Pairs with the smp_load_acquire() in psi_trigger_poll() */
        smp_store_release(&seq->private, new);
}}}

Thanks,
Pintu

Patchew 2.1-devel-b67e4c2

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