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. 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)); + }; 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, }; -- Jens Axboe
