On 11/19/24 5:08 PM, Guenter Roeck wrote: > On 11/19/24 14:30, Jens Axboe wrote: >> On 11/19/24 2:46 PM, Guenter Roeck wrote: >>> On 11/19/24 11:49, Jens Axboe wrote: >>>> On 11/19/24 12:44 PM, Jens Axboe wrote: >>>>> 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. >>>> >>>> Ala the below, perhaps alignment takes care of itself then? >>>> >>> >>> No, that doesn't work (I tried), at least not on its own, because the pointer >>> is still unaligned on m68k. >> >> Yeah we'll likely need to force it. The below should work, I pressume? >> Feels pretty odd to have to align it to the size of it, when that should >> naturally occur... Crusty legacy archs. >> > > Yes, that works. Feel free to add > > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> > > to an official patch. Thanks for testing, will add that and send it out (and queue it up for later this merge window). -- Jens Axboe
