objpool: fix minimum alignment of 'struct objpool_slot'

[PATCH] objpool: fix minimum alignment of 'struct objpool_slot'

Posted by Arnd Bergmann 1 month, 3 weeks ago

From: Arnd Bergmann <arnd@arndb.de>

Members of objpool_slot get passed into try_cmpxchg_release(),
which does not work on most architectures unless they are
naturally aligned. Marking the structure as packed makes it
only byte-aligned, as shown by this (normally disabled) warning:

include/linux/objpool.h:156:56: warning: taking address of packed member of 'struct objpool_slot' may result in an unaligned pointer value [-Waddress-of-packed-member]
  156 |                 if (try_cmpxchg_release(&slot->head, &head, head + 1))
      |                                                       ~^~~~~~~~~~~~

As the struct members are all tightly packed on all architectures,
Just remove the '__packed annotation to give it the required
alignment of the native word size.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/linux/objpool.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/objpool.h b/include/linux/objpool.h
index b713a1fe7521..f678b35b20b1 100644
--- a/include/linux/objpool.h
+++ b/include/linux/objpool.h
@@ -56,7 +56,7 @@ struct objpool_slot {
 	uint32_t            last;
 	uint32_t            mask;
 	void               *entries[];
-} __packed;
+};
 
 struct objpool_head;
 
-- 
2.39.5

Re: [PATCH] objpool: fix minimum alignment of 'struct objpool_slot'

Posted by Yury Norov 1 month, 2 weeks ago

Hi Arnd,

Would you like me to route this with my branch? Please let me know if
anything needed on my side.

Thanks,
Yury

On Tue, Feb 10, 2026 at 11:35:24AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Members of objpool_slot get passed into try_cmpxchg_release(),
> which does not work on most architectures unless they are
> naturally aligned. Marking the structure as packed makes it
> only byte-aligned, as shown by this (normally disabled) warning:
> 
> include/linux/objpool.h:156:56: warning: taking address of packed member of 'struct objpool_slot' may result in an unaligned pointer value [-Waddress-of-packed-member]
>   156 |                 if (try_cmpxchg_release(&slot->head, &head, head + 1))
>       |                                                       ~^~~~~~~~~~~~
> 
> As the struct members are all tightly packed on all architectures,
> Just remove the '__packed annotation to give it the required
> alignment of the native word size.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/linux/objpool.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/objpool.h b/include/linux/objpool.h
> index b713a1fe7521..f678b35b20b1 100644
> --- a/include/linux/objpool.h
> +++ b/include/linux/objpool.h
> @@ -56,7 +56,7 @@ struct objpool_slot {
>  	uint32_t            last;
>  	uint32_t            mask;
>  	void               *entries[];
> -} __packed;
> +};
>  
>  struct objpool_head;
>  
> -- 
> 2.39.5

Re: [PATCH] objpool: fix minimum alignment of 'struct objpool_slot'

Posted by wuqiang.matt 1 month, 2 weeks ago

On 2026/2/10 18:35, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Members of objpool_slot get passed into try_cmpxchg_release(),
> which does not work on most architectures unless they are
> naturally aligned. Marking the structure as packed makes it
> only byte-aligned, as shown by this (normally disabled) warning:
> 
> include/linux/objpool.h:156:56: warning: taking address of packed member of 'struct objpool_slot' may result in an unaligned pointer value [-Waddress-of-packed-member]
>    156 |                 if (try_cmpxchg_release(&slot->head, &head, head + 1))
>        |                                                       ~^~~~~~~~~~~~
> 
> As the struct members are all tightly packed on all architectures,
> Just remove the '__packed annotation to give it the required
> alignment of the native word size.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   include/linux/objpool.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/objpool.h b/include/linux/objpool.h
> index b713a1fe7521..f678b35b20b1 100644
> --- a/include/linux/objpool.h
> +++ b/include/linux/objpool.h
> @@ -56,7 +56,7 @@ struct objpool_slot {
>   	uint32_t            last;
>   	uint32_t            mask;
>   	void               *entries[];
> -} __packed;
> +};
>   
>   struct objpool_head;
>   

Reviewed-by: wuqiang.matt <wuqiang.matt@bytedance.com>

Regards,
Matt Wu

Re: [PATCH] objpool: fix minimum alignment of 'struct objpool_slot'

Posted by Yury Norov 1 month, 2 weeks ago

On Tue, Feb 10, 2026 at 11:35:24AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Members of objpool_slot get passed into try_cmpxchg_release(),
> which does not work on most architectures unless they are
> naturally aligned. Marking the structure as packed makes it
> only byte-aligned, as shown by this (normally disabled) warning:
> 
> include/linux/objpool.h:156:56: warning: taking address of packed member of 'struct objpool_slot' may result in an unaligned pointer value [-Waddress-of-packed-member]
>   156 |                 if (try_cmpxchg_release(&slot->head, &head, head + 1))
>       |                                                       ~^~~~~~~~~~~~
> 
> As the struct members are all tightly packed on all architectures,
> Just remove the '__packed annotation to give it the required
> alignment of the native word size.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Yury Norov <ynorov@nvidia.com>

> ---
>  include/linux/objpool.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/objpool.h b/include/linux/objpool.h
> index b713a1fe7521..f678b35b20b1 100644
> --- a/include/linux/objpool.h
> +++ b/include/linux/objpool.h
> @@ -56,7 +56,7 @@ struct objpool_slot {
>  	uint32_t            last;
>  	uint32_t            mask;
>  	void               *entries[];
> -} __packed;
> +};
>  
>  struct objpool_head;
>  
> -- 
> 2.39.5