Hi Jens, CC Christian (who added the check) CC Vlastimil (who suggested the check) On Tue, Nov 19, 2024 at 11:30 PM Jens Axboe <axboe@xxxxxxxxx> 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 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. > > diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h > index 593c10a02144..8ed9c6923668 100644 > --- a/include/linux/io_uring_types.h > +++ b/include/linux/io_uring_types.h > @@ -674,7 +674,11 @@ struct io_kiocb { > struct io_kiocb *link; > /* custom credentials, valid IFF REQ_F_CREDS is set */ > const struct cred *creds; > - struct io_wq_work work; > + > + union { > + struct io_wq_work work; > + freeptr_t freeptr __aligned(sizeof(freeptr_t)); I'd rather add the __aligned() to the definition of freeptr_t, so it applies to all (future) users. But my main question stays: why is the slab code checking IS_ALIGNED(args->freeptr_offset, sizeof(freeptr_t)? Perhaps that was just intended to be __alignof__ instead of sizeof()? > + }; > > struct { > u64 extra1; > diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c > index 73af59863300..86ac7df2a601 100644 > --- a/io_uring/io_uring.c > +++ b/io_uring/io_uring.c > @@ -3812,7 +3812,7 @@ static int __init io_uring_init(void) > struct kmem_cache_args kmem_args = { > .useroffset = offsetof(struct io_kiocb, cmd.data), > .usersize = sizeof_field(struct io_kiocb, cmd.data), > - .freeptr_offset = offsetof(struct io_kiocb, work), > + .freeptr_offset = offsetof(struct io_kiocb, freeptr), > .use_freeptr_offset = true, > }; Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx 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
