2022-12-04 05:27:05

by mawupeng

Subject: [PATCH -next 1/1] percpu: cleanup invalid assignment to err in pcpu_alloc

From: Ma Wupeng <[email protected]>

Assignment to err if is_atomic is true will never be used since warn
message can only be shown if is_atomic is false after label fail. So drop
it.

Signed-off-by: Ma Wupeng <[email protected]>
---
mm/percpu.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index acd78da0493b..df86d79325b2 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1817,10 +1817,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,

spin_unlock_irqrestore(&pcpu_lock, flags);

- if (is_atomic) {
- err = "atomic alloc failed, no space left";
+ if (is_atomic)
goto fail;
- }

/* No space left. Create a new chunk. */
if (list_empty(&pcpu_chunk_lists[pcpu_free_slot])) {
--
2.25.1

2022-12-04 12:32:11

by Baoquan He

Subject: Re: [PATCH -next 1/1] percpu: cleanup invalid assignment to err in pcpu_alloc

On 12/04/22 at 11:14am, Wupeng Ma wrote:
> From: Ma Wupeng <[email protected]>
>
> Assignment to err if is_atomic is true will never be used since warn
> message can only be shown if is_atomic is false after label fail. So drop
> it.
>
> Signed-off-by: Ma Wupeng <[email protected]>
> ---
> mm/percpu.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index acd78da0493b..df86d79325b2 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1817,10 +1817,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>
> spin_unlock_irqrestore(&pcpu_lock, flags);
>
> - if (is_atomic) {
> - err = "atomic alloc failed, no space left";
> + if (is_atomic)
> goto fail;
> - }

This is good catch. But I think Dennis may not like this way because he
added the message intentionally in commit 11df02bf9bc1 ("percpu: resolve
err may not be initialized in pcpu_alloc").

Can we change the conditional checking in fail part as below?

diff --git a/mm/percpu.c b/mm/percpu.c
index 27697b2429c2..0ac55500fad9 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1897,7 +1897,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
fail:
trace_percpu_alloc_percpu_fail(reserved, is_atomic, size, align);

- if (!is_atomic && do_warn && warn_limit) {
+ if (do_warn && warn_limit) {
pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s\n",
size, align, is_atomic, err);
dump_stack();

2022-12-04 17:37:46

by Christoph Lameter

Subject: Re: [PATCH -next 1/1] percpu: cleanup invalid assignment to err in pcpu_alloc

On Sun, 4 Dec 2022, Baoquan He wrote:

> Can we change the conditional checking in fail part as below?

Yes please. This is potentially a rare condition that should get some
visibility.

2022-12-05 00:47:29

by Dennis Zhou

Subject: Re: [PATCH -next 1/1] percpu: cleanup invalid assignment to err in pcpu_alloc

Hi Baoquan and Wupeng,

On Sun, Dec 04, 2022 at 08:11:23PM +0800, Baoquan He wrote:
> On 12/04/22 at 11:14am, Wupeng Ma wrote:
> > From: Ma Wupeng <[email protected]>
> >
> > Assignment to err if is_atomic is true will never be used since warn
> > message can only be shown if is_atomic is false after label fail. So drop
> > it.
> >
> > Signed-off-by: Ma Wupeng <[email protected]>
> > ---
> > mm/percpu.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index acd78da0493b..df86d79325b2 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -1817,10 +1817,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
> >
> > spin_unlock_irqrestore(&pcpu_lock, flags);
> >
> > - if (is_atomic) {
> > - err = "atomic alloc failed, no space left";
> > + if (is_atomic)
> > goto fail;
> > - }
>
> This is good catch. But I think Dennis may not like this way because he
> added the message intentionally in commit 11df02bf9bc1 ("percpu: resolve
> err may not be initialized in pcpu_alloc").
>

You're right Baoquan haha. I agree with Christoph as well we should
surface atomic.

Though I don't think below is quite right either. We should likely have
a separate warn_limit for atomic and I need to think about dump_stack()
if there are any requirements there.

Thanks,
Dennis

> Can we change the conditional checking in fail part as below?
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 27697b2429c2..0ac55500fad9 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1897,7 +1897,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
> fail:
> trace_percpu_alloc_percpu_fail(reserved, is_atomic, size, align);
>
> - if (!is_atomic && do_warn && warn_limit) {
> + if (do_warn && warn_limit) {
> pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s\n",
> size, align, is_atomic, err);
> dump_stack();
>

2022-12-05 02:40:19

by Baoquan He

Subject: Re: [PATCH -next 1/1] percpu: cleanup invalid assignment to err in pcpu_alloc

On 12/04/22 at 04:30pm, Dennis Zhou wrote:
> Hi Baoquan and Wupeng,
>
> On Sun, Dec 04, 2022 at 08:11:23PM +0800, Baoquan He wrote:
> > On 12/04/22 at 11:14am, Wupeng Ma wrote:
> > > From: Ma Wupeng <[email protected]>
> > >
> > > Assignment to err if is_atomic is true will never be used since warn
> > > message can only be shown if is_atomic is false after label fail. So drop
> > > it.
> > >
> > > Signed-off-by: Ma Wupeng <[email protected]>
> > > ---
> > > mm/percpu.c | 4 +---
> > > 1 file changed, 1 insertion(+), 3 deletions(-)
> > >
> > > diff --git a/mm/percpu.c b/mm/percpu.c
> > > index acd78da0493b..df86d79325b2 100644
> > > --- a/mm/percpu.c
> > > +++ b/mm/percpu.c
> > > @@ -1817,10 +1817,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
> > >
> > > spin_unlock_irqrestore(&pcpu_lock, flags);
> > >
> > > - if (is_atomic) {
> > > - err = "atomic alloc failed, no space left";
> > > + if (is_atomic)
> > > goto fail;
> > > - }
> >
> > This is good catch. But I think Dennis may not like this way because he
> > added the message intentionally in commit 11df02bf9bc1 ("percpu: resolve
> > err may not be initialized in pcpu_alloc").
> >
>
> You're right Baoquan haha. I agree with Christoph as well we should
> surface atomic.
>
> Though I don't think below is quite right either. We should likely have
> a separate warn_limit for atomic and I need to think about dump_stack()
> if there are any requirements there.

Yeah, sounds reasonable. I didn't think it over.

>
>
> > Can we change the conditional checking in fail part as below?
> >
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index 27697b2429c2..0ac55500fad9 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -1897,7 +1897,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
> > fail:
> > trace_percpu_alloc_percpu_fail(reserved, is_atomic, size, align);
> >
> > - if (!is_atomic && do_warn && warn_limit) {
> > + if (do_warn && warn_limit) {
> > pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s\n",
> > size, align, is_atomic, err);
> > dump_stack();
> >
>