Re: [PATCH 03/14] io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache

[Guenter Roeck <linux@roeck-us.net>]

On 11/19/24 08:02, Jens Axboe wrote:
> On 11/19/24 8:36 AM, Guenter Roeck wrote:
>> Hi,
>>
>> On Tue, Oct 29, 2024 at 09:16:32AM -0600, Jens Axboe wrote:
>>> Doesn't matter right now as there's still some bytes left for it, but
>>> let's prepare for the io_kiocb potentially growing and add a specific
>>> freeptr offset for it.
>>>
>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> This patch triggers:
>>
>> 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-mac-00971-g158f238aa69d #1
>> Stack from 00c63e5c:
>>          00c63e5c 00612c1c 00612c1c 00000300 00000001 005f3ce6 004b9044 00612c1c
>>          004ae21e 00000310 000000b6 005f3ce6 005f3ce6 ffffffea ffffffea 00797244
>>          00c63f20 000c6974 005ee588 004c9051 005f3ce6 ffffffea 000000a5 00c614a0
>>          004a72c2 0002cb62 000c675e 004adb58 0076f28a 005f3ce6 000000b6 00c63ef4
>>          00000310 00c63ef4 00000000 00000016 0076f23e 00c63f4c 00000010 00000004
>>          00000038 0000009a 01000000 00000000 00000000 00000000 000020e0 0076f23e
>> Call Trace: [<004b9044>] dump_stack+0xc/0x10
>>   [<004ae21e>] panic+0xc4/0x252
>>   [<000c6974>] __kmem_cache_create_args+0x216/0x26c
>>   [<004a72c2>] strcpy+0x0/0x1c
>>   [<0002cb62>] parse_args+0x0/0x1f2
>>   [<000c675e>] __kmem_cache_create_args+0x0/0x26c
>>   [<004adb58>] memset+0x0/0x8c
>>   [<0076f28a>] io_uring_init+0x4c/0xca
>>   [<0076f23e>] io_uring_init+0x0/0xca
>>   [<000020e0>] do_one_initcall+0x32/0x192
>>   [<0076f23e>] io_uring_init+0x0/0xca
>>   [<0000211c>] do_one_initcall+0x6e/0x192
>>   [<004a72c2>] strcpy+0x0/0x1c
>>   [<0002cb62>] parse_args+0x0/0x1f2
>>   [<000020ae>] do_one_initcall+0x0/0x192
>>   [<0075c4e2>] kernel_init_freeable+0x1a0/0x1a4
>>   [<0076f23e>] io_uring_init+0x0/0xca
>>   [<004b911a>] kernel_init+0x0/0xec
>>   [<004b912e>] kernel_init+0x14/0xec
>>   [<004b911a>] kernel_init+0x0/0xec
>>   [<0000252c>] ret_from_kernel_thread+0xc/0x14
>>
>> when trying to boot the m68k:q800 machine in qemu.
>>
>> An added debug message in create_cache() shows the reason:
>>
>> #### freeptr_offset=154 object_size=182 flags=0x310 aligned=0 sizeof(freeptr_t)=4
>>
>> freeptr_offset would need to be 4-byte aligned but that is not the
>> case on m68k.
> 
> Why is ->work 2-byte aligned to begin with on m68k?!
> 

My understanding is that m68k does not align pointers.

Copying Geert and the m68k mailing list for feedback. Sorry, I should have done
that earlier.

Guenter