From: Guenter Roeck <linux@roeck-us.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>, Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
David Sterba <dsterba@suse.com>,
Miklos Szeredi <miklos@szeredi.hu>,
Anton Altaparmakov <anton@tuxera.com>,
David Howells <dhowells@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Pavel Begunkov <asml.silence@gmail.com>
Subject: Re: [PATCH] iov_iter: separate direction from flavour
Date: Sun, 4 Jul 2021 13:28:44 -0700 [thread overview]
Message-ID: <19689998-9dfe-76a8-30d4-162648e04480@roeck-us.net> (raw)
In-Reply-To: <CAHk-=wj_AROgVZQ1=8mmYCXyu9JujGbNbxp+emGr5i3FagDayw@mail.gmail.com>
On 7/4/21 12:04 PM, Linus Torvalds wrote:
> On Sun, Jul 4, 2021 at 11:54 AM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> No, I still see the same warning, with the same traceback. I did make sure
>> that the code is executed by adding a printk in front of it.
>
> And that printk() hits before the WARN_ON_ONCE() hits?
>
Yes:
[ 8.604785] Run /init as init process
[ 8.604933] ##################### calling force_uaccess_begin()
[ 8.609691] ------------[ cut here ]------------
[ 8.609795] WARNING: CPU: 0 PID: 1 at lib/iov_iter.c:468 iov_iter_init+0x35/0x58
[ 8.609979] CPU: 0 PID: 1 Comm: init Not tainted 5.13.0-09608-g678b12cd4025-dirty #1
Either case, the code doesn't do anything, because force_uaccess_begin() is
already called. With more added debugging:
##################### calling force_uaccess_begin()
############## force_uaccess_begin(), called from run_init_process+0x80/0x8c
############## force_uaccess_begin(), called from load_flat_binary+0x10e/0x92a
> Funky. That sounds to me like something is then doing
> set_fs(KERNEL_DS) again later, but it's also possible that I've been
> dropped on my head a few too many times as a young child, and am
> missing something completely obvious.
>
> Can somebody put me out of my misery and say "Oh, Linus, please take
> your meds - you're missing xyz..."
>
Turns out that, at least on m68k/nommu, USER_DS and KERNEL_DS are the same.
#define USER_DS MAKE_MM_SEG(TASK_SIZE)
#define KERNEL_DS MAKE_MM_SEG(0xFFFFFFFF)
and:
#define TASK_SIZE (0xFFFFFFFFUL)
I didn't check mps2, but I strongly suspect the same is true there.
Guenter
next prev parent reply other threads:[~2021-07-04 20:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-04 17:29 [PATCH] iov_iter: separate direction from flavour Guenter Roeck
2021-07-04 18:31 ` Linus Torvalds
2021-07-04 18:54 ` Guenter Roeck
2021-07-04 19:04 ` Linus Torvalds
2021-07-04 20:28 ` Guenter Roeck [this message]
2021-07-04 20:41 ` Linus Torvalds
2021-07-04 21:47 ` Guenter Roeck
2021-07-04 22:44 ` Linus Torvalds
2021-07-04 22:47 ` Matthew Wilcox
2021-07-04 22:53 ` Linus Torvalds
2021-07-04 23:34 ` Linus Torvalds
2021-07-05 5:17 ` Christoph Hellwig
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