On 11/19/24 12:41 PM, Geert Uytterhoeven wrote: > Hi Jens, > > On Tue, Nov 19, 2024 at 8:30?PM Jens Axboe <axboe@xxxxxxxxx> wrote: >> On 11/19/24 12:25 PM, Geert Uytterhoeven wrote: >>> On Tue, Nov 19, 2024 at 8:10?PM Jens Axboe <axboe@xxxxxxxxx> wrote: >>>> On 11/19/24 12:02 PM, Geert Uytterhoeven wrote: >>>>> On Tue, Nov 19, 2024 at 8:00?PM Jens Axboe <axboe@xxxxxxxxx> wrote: >>>>>> On 11/19/24 10:49 AM, Geert Uytterhoeven wrote: >>>>>>> On Tue, Nov 19, 2024 at 5:21?PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: >>>>>>>> On 11/19/24 08:02, Jens Axboe wrote: >>>>>>>>> On 11/19/24 8:36 AM, Guenter Roeck wrote: >>>>>>>>>> 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@xxxxxxxxx> >>>>>>>>>> >>>>>>>>>> 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. >>>>>>> >>>>>>> The minimum alignment for multi-byte integral values on m68k is >>>>>>> 2 bytes. >>>>>>> >>>>>>> See also the comment at >>>>>>> https://elixir.bootlin.com/linux/v6.12/source/include/linux/maple_tree.h#L46 >>>>>> >>>>>> Maybe it's time we put m68k to bed? :-) >>>>>> >>>>>> We can add a forced alignment ->work to be 4 bytes, won't change >>>>>> anything on anything remotely current. But does feel pretty hacky to >>>>>> need to align based on some ancient thing. >>>>> >>>>> Why does freeptr_offset need to be 4-byte aligned? >>>> >>>> Didn't check, but it's slab/slub complaining using a 2-byte aligned >>>> address for the free pointer offset. It's explicitly checking: >>>> >>>> /* If a custom freelist pointer is requested make sure it's sane. */ >>>> err = -EINVAL; >>>> if (args->use_freeptr_offset && >>>> (args->freeptr_offset >= object_size || >>>> !(flags & SLAB_TYPESAFE_BY_RCU) || >>>> !IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t)))) >>>> goto out; >>> >>> It is not guaranteed that alignof(freeptr_t) >= sizeof(freeptr_t) >>> (free_ptr is sort of a long). If freeptr_offset must be a multiple of >>> 4 or 8 bytes, >>> the code that assigns it must make sure that is true. >> >> Right, this is what the email is about... >> >>> I guess this is the code in fs/file_table.c: >>> >>> .freeptr_offset = offsetof(struct file, f_freeptr), >>> >>> which references: >>> >>> include/linux/fs.h: freeptr_t f_freeptr; >>> >>> I guess the simplest solution is to add an __aligned(sizeof(freeptr_t)) >>> (or __aligned(sizeof(long)) to the definition of freeptr_t: >>> >>> include/linux/slab.h:typedef struct { unsigned long v; } freeptr_t; >> >> It's not, it's struct io_kiocb->work, as per the stack trace in this >> email. > > Sorry, I was falling out of thin air into this thread... > > linux-next/master:io_uring/io_uring.c: .freeptr_offset = > offsetof(struct io_kiocb, work), > linux-next/master:io_uring/io_uring.c: .use_freeptr_offset = true, > > Apparently io_kiocb.work is of type struct io_wq_work, not freeptr_t? > Isn't that a bit error-prone, as the slab core code expects a freeptr_t? It just needs the space, should not matter otherwise. But may as well just add the union and align the freeptr so it stop complaining on m68k. -- Jens Axboe
