2023-07-18 06:40:43

by Ran Sun

Subject: [PATCH] mm/percpu.c: change GFP_KERNEL to GFP_ATOMIC

ERROR: function pcpu_balance_populated called on line 2238 inside lock
on line 2234 but uses GFP_KERNEL

Generated by: scripts/coccinelle/locks/call_kern.cocci

Signed-off-by: Ran Sun <[email protected]>
---
mm/percpu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 28e07ede46f6..d8809c7511cd 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2033,7 +2033,7 @@ static void pcpu_balance_free(bool empty_only)
static void pcpu_balance_populated(void)
{
/* gfp flags passed to underlying allocators */
- const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
+ const gfp_t gfp = GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
struct pcpu_chunk *chunk;
int slot, nr_to_pop, ret;

2023-07-18 18:09:15

by Andrew Morton

Subject: Re: [PATCH] mm/percpu.c: change GFP_KERNEL to GFP_ATOMIC

On Tue, 18 Jul 2023 14:35:11 +0800 [email protected] wrote:

> ERROR: function pcpu_balance_populated called on line 2238 inside lock
> on line 2234 but uses GFP_KERNEL
>
> Generated by: scripts/coccinelle/locks/call_kern.cocci
>
> ...
>
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2033,7 +2033,7 @@ static void pcpu_balance_free(bool empty_only)
> static void pcpu_balance_populated(void)
> {
> /* gfp flags passed to underlying allocators */
> - const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
> + const gfp_t gfp = GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
> struct pcpu_chunk *chunk;
> int slot, nr_to_pop, ret;

I don't believe this warning is correct.

spin_unlock_irq(&pcpu_lock);
ret = pcpu_populate_chunk(chunk, rs, rs + nr, gfp);
cond_resched();
spin_lock_irq(&pcpu_lock);

2023-07-21 00:05:28

by Baoquan He

Subject: Re: [PATCH] mm/percpu.c: change GFP_KERNEL to GFP_ATOMIC

On 07/18/23 at 10:17am, Andrew Morton wrote:
> On Tue, 18 Jul 2023 14:35:11 +0800 [email protected] wrote:
>
> > ERROR: function pcpu_balance_populated called on line 2238 inside lock
> > on line 2234 but uses GFP_KERNEL
> >
> > Generated by: scripts/coccinelle/locks/call_kern.cocci
> >
> > ...
> >
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -2033,7 +2033,7 @@ static void pcpu_balance_free(bool empty_only)
> > static void pcpu_balance_populated(void)
> > {
> > /* gfp flags passed to underlying allocators */
> > - const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
> > + const gfp_t gfp = GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
> > struct pcpu_chunk *chunk;
> > int slot, nr_to_pop, ret;
>
> I don't believe this warning is correct.

Yeah, the warning is false positive. It releases the lock when
requesting memory allocation, then take the lock again.

>
> spin_unlock_irq(&pcpu_lock);
> ret = pcpu_populate_chunk(chunk, rs, rs + nr, gfp);
> cond_resched();
> spin_lock_irq(&pcpu_lock);
>