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[209.85.219.179]) by smtp.gmail.com with ESMTPSA id 00721157ae682-6ee71341fb2sm18826577b3.86.2024.11.19.11.41.43 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Nov 2024 11:41:43 -0800 (PST) Received: by mail-yb1-f179.google.com with SMTP id 3f1490d57ef6-e387fdd1ec4so2409672276.0 for ; Tue, 19 Nov 2024 11:41:43 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCX3pBpVUPraY6EyI4RUbHspXOV/1KEnUMPcsL/L9H3c8Rdr4ij7AYv0ZTG+5x8cWQbiYiOza8gEOA==@vger.kernel.org X-Received: by 2002:a05:690c:4b87:b0:6dd:b983:8563 with SMTP id 00721157ae682-6eebd127174mr830357b3.14.1732045302718; Tue, 19 Nov 2024 11:41:42 -0800 (PST) Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20241029152249.667290-1-axboe@kernel.dk> <20241029152249.667290-4-axboe@kernel.dk> <37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net> <5a7528c4-4391-4bd9-bbdb-a0247f3c76a9@kernel.dk> <5851cd28-b369-4c09-876c-62c4a47c5982@kernel.dk> <358710e8-a826-46df-9846-5a9e0f7c6851@kernel.dk> In-Reply-To: <358710e8-a826-46df-9846-5a9e0f7c6851@kernel.dk> From: Geert Uytterhoeven Date: Tue, 19 Nov 2024 20:41:30 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 03/14] io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache To: Jens Axboe Cc: Guenter Roeck , io-uring@vger.kernel.org, linux-m68k Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Jens, On Tue, Nov 19, 2024 at 8:30=E2=80=AFPM Jens Axboe wrote: > On 11/19/24 12:25 PM, Geert Uytterhoeven wrote: > > On Tue, Nov 19, 2024 at 8:10?PM Jens Axboe wrote: > >> On 11/19/24 12:02 PM, Geert Uytterhoeven wrote: > >>> On Tue, Nov 19, 2024 at 8:00?PM Jens Axboe wrote: > >>>> On 11/19/24 10:49 AM, Geert Uytterhoeven wrote: > >>>>> On Tue, Nov 19, 2024 at 5:21?PM Guenter Roeck = 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 i= t, but > >>>>>>>>> let's prepare for the io_kiocb potentially growing and add a sp= ecific > >>>>>>>>> freeptr offset for it. > >>>>>>>>> > >>>>>>>>> Signed-off-by: Jens Axboe > >>>>>>>> > >>>>>>>> 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 0= 04b9044 00612c1c > >>>>>>>> 004ae21e 00000310 000000b6 005f3ce6 005f3ce6 ffffffea f= fffffea 00797244 > >>>>>>>> 00c63f20 000c6974 005ee588 004c9051 005f3ce6 ffffffea 0= 00000a5 00c614a0 > >>>>>>>> 004a72c2 0002cb62 000c675e 004adb58 0076f28a 005f3ce6 0= 00000b6 00c63ef4 > >>>>>>>> 00000310 00c63ef4 00000000 00000016 0076f23e 00c63f4c 0= 0000010 00000004 > >>>>>>>> 00000038 0000009a 01000000 00000000 00000000 00000000 0= 00020e0 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=3D154 object_size=3D182 flags=3D0x310 aligne= d=3D0 sizeof(freeptr_t)=3D4 > >>>>>>>> > >>>>>>>> freeptr_offset would need to be 4-byte aligned but that is not t= he > >>>>>>>> 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_t= ree.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 sa= ne. */ > >> err =3D -EINVAL; > >> if (args->use_freeptr_offset && > >> (args->freeptr_offset >=3D 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) >=3D 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 =3D 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 =3D offsetof(struct io_kiocb, work), linux-next/master:io_uring/io_uring.c: .use_freeptr_offset =3D tru= e, 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? Gr{oetje,eeting}s, Geert --=20 Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k= .org In personal conversations with technical people, I call myself a hacker. Bu= t when I'm talking to journalists I just say "programmer" or something like t= hat. -- Linus Torvalds