From: Linus Torvalds <torvalds@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>,
Andreas Gruenbacher <agruenba@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Will Deacon <will@kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults
Date: Wed, 24 Nov 2021 15:00:00 -0800 [thread overview]
Message-ID: <CAHk-=wgHqjX3kenSk5_bCRM+ZC-tgndBMfbVVsbp0CwJf2DU-w@mail.gmail.com> (raw)
In-Reply-To: <YZ6arlsi2L3LVbFO@casper.infradead.org>
Catalin talked about the other change, but this part:
On Wed, Nov 24, 2021 at 12:04 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> (where __copy_to_user_nofault() is a new function that does exactly what
> copy_to_user_nofault() does, but returns the number of bytes copied)
If we want the "how many bytes" part, then we should just make
copy_to_user_nofault() have the same semantics as a plain
copy_to_user().
IOW, change it to return "number of bytes not copied".
Lookin gat the current uses, such a change would be trivial. The only
case that wants a 0/-EFAULT error is the bpf_probe_write_user(),
everybody else already just wants "zero for success", so changing
copy_to_user_nofault() would be trivial.
And it really is odd and very non-intuitive that
copy_to_user_nofault() has a completely different return value from
copy_to_user().
So if _anybody_ wants a byte-count, that should just be fixed.
Linus
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next prev parent reply other threads:[~2021-11-24 23:01 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-24 19:20 [PATCH 0/3] Avoid live-lock in fault-in+uaccess loops with sub-page faults Catalin Marinas
2021-11-24 19:20 ` [PATCH 1/3] mm: Introduce fault_in_exact_writeable() to probe for " Catalin Marinas
2021-11-24 19:20 ` [PATCH 2/3] arm64: Add support for sub-page faults user probing Catalin Marinas
2021-11-24 19:20 ` [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults Catalin Marinas
2021-11-24 20:03 ` Matthew Wilcox
2021-11-24 20:37 ` Catalin Marinas
2021-11-25 22:25 ` Andreas Gruenbacher
2021-11-25 22:42 ` Catalin Marinas
2021-11-26 22:29 ` Andreas Gruenbacher
2021-11-26 22:57 ` Catalin Marinas
2021-11-27 3:52 ` Andreas Gruenbacher
2021-11-27 14:33 ` Catalin Marinas
2021-11-27 12:39 ` Andreas Gruenbacher
2021-11-27 15:21 ` Catalin Marinas
2021-11-27 18:05 ` Andreas Gruenbacher
2021-11-29 12:16 ` Catalin Marinas
2021-11-29 13:33 ` Andreas Gruenbacher
2021-11-29 15:36 ` Catalin Marinas
2021-11-29 18:40 ` Linus Torvalds
2021-11-29 19:31 ` Andreas Gruenbacher
2021-11-29 20:56 ` Catalin Marinas
2021-11-29 21:53 ` Linus Torvalds
2021-11-29 23:12 ` Catalin Marinas
2021-11-29 13:52 ` Catalin Marinas
2021-11-24 23:00 ` Linus Torvalds [this message]
2021-11-25 11:10 ` Catalin Marinas
2021-11-25 18:13 ` Linus Torvalds
2021-11-25 20:43 ` Catalin Marinas
2021-11-25 21:02 ` Matthew Wilcox
2021-11-25 21:29 ` Catalin Marinas
2021-11-25 21:40 ` Andreas Gruenbacher
2021-11-26 16:42 ` David Sterba
2021-11-24 21:36 ` [PATCH 0/3] Avoid live-lock in fault-in+uaccess loops " Andrew Morton
2021-11-24 22:31 ` Catalin Marinas
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