[PATCH] slab: Fix too strict alignment check in create_cache()

[PATCH] slab: Fix too strict alignment check in create_cache()

[Geert Uytterhoeven]

On m68k, where the minimum alignment of unsigned long is 2 bytes:

    Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
    CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
    Stack from 0102fe5c:
	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
    Call Trace: [<00425e78>] dump_stack+0xc/0x10
     [<0041eb74>] panic+0xd8/0x26c
     [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
     [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
     [<0041e5f0>] memset+0x0/0x8c
     [<005f67c0>] io_uring_init+0x54/0xd2

The minimal alignment of an integral type may differ from its size,
hence is not safe to assume that an arbitrary freeptr_t (which is
basically an unsigned long) is always aligned to 4 or 8 bytes.

As nothing seems to require the additional alignment, it is safe to fix
this by relaxing the check to the actual minimum alignment of freeptr_t.

Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 893d320599151845..f2f201d865c108bd 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
 	if (args->use_freeptr_offset &&
 	    (args->freeptr_offset >= object_size ||
 	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
-	     !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
+	     !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))
 		goto out;
 
 	err = -ENOMEM;
-- 
2.34.1

[PATCH] slab: Fix too strict alignment check in create_cache()

[Geert Uytterhoeven]

On m68k, where the minimum alignment of unsigned long is 2 bytes:

    Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
    CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
    Stack from 0102fe5c:
	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
    Call Trace: [<00425e78>] dump_stack+0xc/0x10
     [<0041eb74>] panic+0xd8/0x26c
     [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
     [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
     [<0041e5f0>] memset+0x0/0x8c
     [<005f67c0>] io_uring_init+0x54/0xd2

The minimal alignment of an integral type may differ from its size,
hence is not safe to assume that an arbitrary freeptr_t (which is
basically an unsigned long) is always aligned to 4 or 8 bytes.

As nothing seems to require the additional alignment, it is safe to fix
this by relaxing the check to the actual minimum alignment of freeptr_t.

Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 893d320599151845..f2f201d865c108bd 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
 	if (args->use_freeptr_offset &&
 	    (args->freeptr_offset >= object_size ||
 	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
-	     !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
+	     !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))
 		goto out;
 
 	err = -ENOMEM;
-- 
2.34.1

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Guenter Roeck]

On Wed, Nov 20, 2024 at 01:46:21PM +0100, Geert Uytterhoeven wrote:
> On m68k, where the minimum alignment of unsigned long is 2 bytes:
> 
>     Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
>     CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
>     Stack from 0102fe5c:
> 	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
> 	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
> 	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
> 	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
> 	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
> 	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
>     Call Trace: [<00425e78>] dump_stack+0xc/0x10
>      [<0041eb74>] panic+0xd8/0x26c
>      [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
>      [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
>      [<0041e5f0>] memset+0x0/0x8c
>      [<005f67c0>] io_uring_init+0x54/0xd2
> 
> The minimal alignment of an integral type may differ from its size,
> hence is not safe to assume that an arbitrary freeptr_t (which is
> basically an unsigned long) is always aligned to 4 or 8 bytes.
> 
> As nothing seems to require the additional alignment, it is safe to fix
> this by relaxing the check to the actual minimum alignment of freeptr_t.
> 
> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

On m68k:

Tested-by: Guenter Roeck <linux@roeck-us.net>

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Jens Axboe]

On 11/20/24 5:49 AM, Geert Uytterhoeven wrote:
> On m68k, where the minimum alignment of unsigned long is 2 bytes:
> 
>     Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
>     CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
>     Stack from 0102fe5c:
> 	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
> 	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
> 	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
> 	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
> 	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
> 	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
>     Call Trace: [<00425e78>] dump_stack+0xc/0x10
>      [<0041eb74>] panic+0xd8/0x26c
>      [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
>      [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
>      [<0041e5f0>] memset+0x0/0x8c
>      [<005f67c0>] io_uring_init+0x54/0xd2
> 
> The minimal alignment of an integral type may differ from its size,
> hence is not safe to assume that an arbitrary freeptr_t (which is
> basically an unsigned long) is always aligned to 4 or 8 bytes.
> 
> As nothing seems to require the additional alignment, it is safe to fix
> this by relaxing the check to the actual minimum alignment of freeptr_t.
> 
> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 893d320599151845..f2f201d865c108bd 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
>  	if (args->use_freeptr_offset &&
>  	    (args->freeptr_offset >= object_size ||
>  	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
> -	     !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
> +	     !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))
>  		goto out;
>  
>  	err = -ENOMEM;

This looks much better, thanks.

Reviewed-by: Jens Axboe <axboe@kernel.dk>

-- 
Jens Axboe

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Vlastimil Babka]

On 11/20/24 13:49, Geert Uytterhoeven wrote:
> On m68k, where the minimum alignment of unsigned long is 2 bytes:
> 
>     Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
>     CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
>     Stack from 0102fe5c:
> 	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
> 	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
> 	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
> 	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
> 	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
> 	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
>     Call Trace: [<00425e78>] dump_stack+0xc/0x10
>      [<0041eb74>] panic+0xd8/0x26c
>      [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
>      [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
>      [<0041e5f0>] memset+0x0/0x8c
>      [<005f67c0>] io_uring_init+0x54/0xd2
> 
> The minimal alignment of an integral type may differ from its size,
> hence is not safe to assume that an arbitrary freeptr_t (which is
> basically an unsigned long) is always aligned to 4 or 8 bytes.
> 
> As nothing seems to require the additional alignment, it is safe to fix
> this by relaxing the check to the actual minimum alignment of freeptr_t.
> 
> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Thanks, will add it to slab pull for 6.13.

> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 893d320599151845..f2f201d865c108bd 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
>  	if (args->use_freeptr_offset &&
>  	    (args->freeptr_offset >= object_size ||
>  	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
> -	     !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
> +	     !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))

Seems only bunch of places uses __alignof but many use __alignoff__ and this
also is what seems to be documented?

>  		goto out;
>  
>  	err = -ENOMEM;

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Guenter Roeck]

On 11/20/24 07:03, Vlastimil Babka wrote:
> On 11/20/24 13:49, Geert Uytterhoeven wrote:
>> On m68k, where the minimum alignment of unsigned long is 2 bytes:
>>
>>      Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
>>      CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
>>      Stack from 0102fe5c:
>> 	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
>> 	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
>> 	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
>> 	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
>> 	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
>> 	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
>>      Call Trace: [<00425e78>] dump_stack+0xc/0x10
>>       [<0041eb74>] panic+0xd8/0x26c
>>       [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
>>       [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
>>       [<0041e5f0>] memset+0x0/0x8c
>>       [<005f67c0>] io_uring_init+0x54/0xd2
>>
>> The minimal alignment of an integral type may differ from its size,
>> hence is not safe to assume that an arbitrary freeptr_t (which is
>> basically an unsigned long) is always aligned to 4 or 8 bytes.
>>
>> As nothing seems to require the additional alignment, it is safe to fix
>> this by relaxing the check to the actual minimum alignment of freeptr_t.
>>
>> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
>> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> 
> Thanks, will add it to slab pull for 6.13.
> 
>> ---
>>   mm/slab_common.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>> index 893d320599151845..f2f201d865c108bd 100644
>> --- a/mm/slab_common.c
>> +++ b/mm/slab_common.c
>> @@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
>>   	if (args->use_freeptr_offset &&
>>   	    (args->freeptr_offset >= object_size ||
>>   	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
>> -	     !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
>> +	     !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))
> 
> Seems only bunch of places uses __alignof but many use __alignoff__ and this
> also is what seems to be documented?

__alignoff__ -> __alignof__

Guenter

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Vlastimil Babka]

On 11/20/24 16:14, Guenter Roeck wrote:
> On 11/20/24 07:03, Vlastimil Babka wrote:
>> On 11/20/24 13:49, Geert Uytterhoeven wrote:
>>> On m68k, where the minimum alignment of unsigned long is 2 bytes:
>>>
>>>      Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
>>>      CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
>>>      Stack from 0102fe5c:
>>> 	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
>>> 	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
>>> 	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
>>> 	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
>>> 	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
>>> 	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
>>>      Call Trace: [<00425e78>] dump_stack+0xc/0x10
>>>       [<0041eb74>] panic+0xd8/0x26c
>>>       [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
>>>       [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
>>>       [<0041e5f0>] memset+0x0/0x8c
>>>       [<005f67c0>] io_uring_init+0x54/0xd2
>>>
>>> The minimal alignment of an integral type may differ from its size,
>>> hence is not safe to assume that an arbitrary freeptr_t (which is
>>> basically an unsigned long) is always aligned to 4 or 8 bytes.
>>>
>>> As nothing seems to require the additional alignment, it is safe to fix
>>> this by relaxing the check to the actual minimum alignment of freeptr_t.
>>>
>>> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
>>> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
>>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>>> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
>>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>> 
>> Thanks, will add it to slab pull for 6.13.
>> 
>>> ---
>>>   mm/slab_common.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>>> index 893d320599151845..f2f201d865c108bd 100644
>>> --- a/mm/slab_common.c
>>> +++ b/mm/slab_common.c
>>> @@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
>>>   	if (args->use_freeptr_offset &&
>>>   	    (args->freeptr_offset >= object_size ||
>>>   	     !(flags & SLAB_TYPESAFE_BY_RCU) ||
>>> -	     !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
>>> +	     !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))
>> 
>> Seems only bunch of places uses __alignof but many use __alignoff__ and this
>> also is what seems to be documented?
> 
> __alignoff__ -> __alignof__

Yeah I meant __alignof__
Will chage it locally then.

> Guenter
> 

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Geert Uytterhoeven]

Hi Vlastimil,

On Wed, Nov 20, 2024 at 4:44 PM Vlastimil Babka <vbabka@suse.cz> wrote:
> On 11/20/24 16:14, Guenter Roeck wrote:
> > On 11/20/24 07:03, Vlastimil Babka wrote:
> >> On 11/20/24 13:49, Geert Uytterhoeven wrote:
> >>> On m68k, where the minimum alignment of unsigned long is 2 bytes:
> >>>
> >>>      Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
> >>>      CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
> >>>      Stack from 0102fe5c:
> >>>         0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
> >>>         0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
> >>>         0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
> >>>         01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
> >>>         00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
> >>>         00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
> >>>      Call Trace: [<00425e78>] dump_stack+0xc/0x10
> >>>       [<0041eb74>] panic+0xd8/0x26c
> >>>       [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
> >>>       [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
> >>>       [<0041e5f0>] memset+0x0/0x8c
> >>>       [<005f67c0>] io_uring_init+0x54/0xd2
> >>>
> >>> The minimal alignment of an integral type may differ from its size,
> >>> hence is not safe to assume that an arbitrary freeptr_t (which is
> >>> basically an unsigned long) is always aligned to 4 or 8 bytes.
> >>>
> >>> As nothing seems to require the additional alignment, it is safe to fix
> >>> this by relaxing the check to the actual minimum alignment of freeptr_t.
> >>>
> >>> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> >>> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> >>> Reported-by: Guenter Roeck <linux@roeck-us.net>
> >>> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> >>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> >>
> >> Thanks, will add it to slab pull for 6.13.
> >>
> >>> ---
> >>>   mm/slab_common.c | 2 +-
> >>>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/mm/slab_common.c b/mm/slab_common.c
> >>> index 893d320599151845..f2f201d865c108bd 100644
> >>> --- a/mm/slab_common.c
> >>> +++ b/mm/slab_common.c
> >>> @@ -230,7 +230,7 @@ static struct kmem_cache *create_cache(const char *name,
> >>>     if (args->use_freeptr_offset &&
> >>>         (args->freeptr_offset >= object_size ||
> >>>          !(flags & SLAB_TYPESAFE_BY_RCU) ||
> >>> -        !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t))))
> >>> +        !IS_ALIGNED(args->freeptr_offset, __alignof(freeptr_t))))
> >>
> >> Seems only bunch of places uses __alignof but many use __alignoff__ and this
> >> also is what seems to be documented?
> >
> > __alignoff__ -> __alignof__
>
> Yeah I meant __alignof__
> Will chage it locally then.

Thank you!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Christoph Lameter (Ampere)]

On Wed, 20 Nov 2024, Vlastimil Babka wrote:

> >
> > Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> > Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> Thanks, will add it to slab pull for 6.13.

Note that there are widespread assumptions in kernel code that the
alignment of scalars is the "natural alignment". Other portions of the
kernel may break. The compiler actually goes along with this??

How do you deal with torn reads/writes in such a scenario? Is this UP
only?

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Matthew Wilcox]

On Wed, Nov 20, 2024 at 09:50:47AM -0800, Christoph Lameter (Ampere) wrote:
> On Wed, 20 Nov 2024, Vlastimil Babka wrote:
> 
> > >
> > > Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> > > Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> > > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > > Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> > > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> >
> > Thanks, will add it to slab pull for 6.13.
> 
> Note that there are widespread assumptions in kernel code that the
> alignment of scalars is the "natural alignment". Other portions of the
> kernel may break. The compiler actually goes along with this??

u64s aren't aligned on x86-32.  it's caused some problems over the
years, but things work ok in general.

> How do you deal with torn reads/writes in such a scenario? Is this UP
> only?

there were never a lot of smp m68k.  not sure i can think of one, tbh.
sun3 and hp300/400 seem like the obvious people who might have done an
smp m68k, but neither did.

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Geert Uytterhoeven]

Hi Christoph,

On Wed, Nov 20, 2024 at 6:50 PM Christoph Lameter (Ampere)
<cl@gentwo.org> wrote:
> On Wed, 20 Nov 2024, Vlastimil Babka wrote:
> > > Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> > > Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> > > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > > Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> > > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> >
> > Thanks, will add it to slab pull for 6.13.
>
> Note that there are widespread assumptions in kernel code that the
> alignment of scalars is the "natural alignment". Other portions of the
> kernel may break. The compiler actually goes along with this??

Linux has supported m68k since last century.
Any new such assumptions are fixed quickly (at least in the kernel).
If you need a specific alignment, make sure to use __aligned and/or
appropriate padding in structures.
And yes, the compiler knows, and provides __alignof__.

> How do you deal with torn reads/writes in such a scenario? Is this UP
> only?

Linux does not support (rate) SMP m68k machines.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] slab: Fix too strict alignment check in create_cache()

[Christian Brauner]

On Wed, Nov 20, 2024 at 01:46:21PM +0100, Geert Uytterhoeven wrote:
> On m68k, where the minimum alignment of unsigned long is 2 bytes:
> 
>     Kernel panic - not syncing: __kmem_cache_create_args: Failed to create slab 'io_kiocb'. Error -22
>     CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.12.0-atari-03776-g7eaa1f99261a #1783
>     Stack from 0102fe5c:
> 	    0102fe5c 00514a2b 00514a2b ffffff00 00000001 0051f5ed 00425e78 00514a2b
> 	    0041eb74 ffffffea 00000310 0051f5ed ffffffea ffffffea 00601f60 00000044
> 	    0102ff20 000e7a68 0051ab8e 004383b8 0051f5ed ffffffea 000000b8 00000007
> 	    01020c00 00000000 000e77f0 0041e5f0 005f67c0 0051f5ed 000000b6 0102fef4
> 	    00000310 0102fef4 00000000 00000016 005f676c 0060a34c 00000010 00000004
> 	    00000038 0000009a 01000000 000000b8 005f668e 0102e000 00001372 0102ff88
>     Call Trace: [<00425e78>] dump_stack+0xc/0x10
>      [<0041eb74>] panic+0xd8/0x26c
>      [<000e7a68>] __kmem_cache_create_args+0x278/0x2e8
>      [<000e77f0>] __kmem_cache_create_args+0x0/0x2e8
>      [<0041e5f0>] memset+0x0/0x8c
>      [<005f67c0>] io_uring_init+0x54/0xd2
> 
> The minimal alignment of an integral type may differ from its size,
> hence is not safe to assume that an arbitrary freeptr_t (which is
> basically an unsigned long) is always aligned to 4 or 8 bytes.
> 
> As nothing seems to require the additional alignment, it is safe to fix
> this by relaxing the check to the actual minimum alignment of freeptr_t.
> 
> Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---

Looks good to me,
Reviewed-by: Christian Brauner <brauner@kernel.org>