From: Linus Torvalds <torvalds@linux-foundation.org>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Patrick McLean <chutzpah@gentoo.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Bruce Fields <bfields@redhat.com>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
stable <stable@vger.kernel.org>,
Thorsten Leemhuis <regressions@leemhuis.info>
Subject: Re: bit tweaks [was: Re: [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11]
Date: Mon, 13 Nov 2017 15:54:24 -0800 [thread overview]
Message-ID: <CA+55aFwWt-hRSRqJRP6Wc67COZFZwpcMy4o06bRNBGnwW8QBFw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFz4qA2RhjW5KtD+=jnbW-9hoRGgDQ5N6DkQ5LCTkO5idA@mail.gmail.com>
On Mon, Nov 13, 2017 at 3:30 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> So let's just rewrite that mnt_flags conversion that way, justr to get
> gcc to generate the obvious code.
Oh wow. I tried to do the same thing in fs/namespace.c where it does
the reverse bit translation, and gcc makes a _horrible_ mess of it and
actually makes the code much worse because for some reason the pattern
doesn't trigger.
So this gcc optimization is apparently pretty damn fragile in general.
It triggers for the trivial cases, but then other code around it can
confuse it badly.
So I don't think I'll touch this, it seems to not be really reliably
something that makes gcc generate what should be the obvious code..
Linus
next prev parent reply other threads:[~2017-11-13 23:54 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-09 0:43 [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11 Patrick McLean
2017-11-09 2:40 ` Linus Torvalds
2017-11-09 3:45 ` Al Viro
2017-11-09 19:34 ` Patrick McLean
2017-11-09 19:38 ` Al Viro
2017-11-09 19:42 ` Patrick McLean
2017-11-09 19:37 ` Al Viro
2017-11-09 19:51 ` Patrick McLean
2017-11-09 20:04 ` Linus Torvalds
2017-11-09 21:16 ` Al Viro
2017-11-10 1:58 ` Patrick McLean
2017-11-10 13:53 ` Arnd Bergmann
2017-11-10 18:42 ` Linus Torvalds
2017-11-10 23:26 ` Patrick McLean
2017-11-11 0:27 ` Patrick McLean
2017-11-11 2:36 ` Linus Torvalds
2017-11-11 2:36 ` [kernel-hardening] " Linus Torvalds
2017-11-11 2:36 ` Linus Torvalds
2017-11-11 16:13 ` Kees Cook
2017-11-11 16:13 ` [kernel-hardening] " Kees Cook
2017-11-11 16:13 ` Kees Cook
2017-11-11 17:31 ` Linus Torvalds
2017-11-11 17:31 ` [kernel-hardening] " Linus Torvalds
2017-11-11 17:31 ` Linus Torvalds
2017-11-13 22:48 ` Patrick McLean
2017-11-13 22:48 ` [kernel-hardening] " Patrick McLean
2017-11-13 22:48 ` Patrick McLean
2017-11-17 0:54 ` Kees Cook
2017-11-17 0:54 ` [kernel-hardening] " Kees Cook
2017-11-17 0:54 ` Kees Cook
2017-11-17 19:03 ` Patrick McLean
2017-11-17 19:03 ` [kernel-hardening] " Patrick McLean
2017-11-17 19:03 ` Patrick McLean
2017-11-17 21:26 ` Kees Cook
2017-11-17 21:26 ` [kernel-hardening] " Kees Cook
2017-11-17 21:26 ` Kees Cook
2017-11-18 0:27 ` Patrick McLean
2017-11-18 0:27 ` [kernel-hardening] " Patrick McLean
2017-11-18 0:27 ` Patrick McLean
2017-11-18 0:55 ` Linus Torvalds
2017-11-18 0:55 ` [kernel-hardening] " Linus Torvalds
2017-11-18 0:55 ` Linus Torvalds
2017-11-18 1:54 ` Patrick McLean
2017-11-18 1:54 ` [kernel-hardening] " Patrick McLean
2017-11-18 1:54 ` Patrick McLean
2017-11-18 5:14 ` Kees Cook
2017-11-18 5:14 ` [kernel-hardening] " Kees Cook
2017-11-18 5:14 ` Kees Cook
2017-11-18 5:29 ` Linus Torvalds
2017-11-18 5:29 ` [kernel-hardening] " Linus Torvalds
2017-11-18 5:29 ` Linus Torvalds
2017-11-18 8:20 ` Kees Cook
2017-11-18 8:20 ` [kernel-hardening] " Kees Cook
2017-11-18 8:20 ` Kees Cook
2018-02-21 22:19 ` RANDSTRUCT structs need linux/compiler_types.h (Was: [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11) Maciej S. Szmigiero
2018-02-21 22:47 ` Linus Torvalds
2018-02-21 22:47 ` Linus Torvalds
2018-02-21 23:34 ` Kees Cook
2018-02-21 23:34 ` Kees Cook
2018-03-05 9:27 ` Masahiro Yamada
2018-03-05 9:27 ` Masahiro Yamada
2018-03-05 19:15 ` Kees Cook
2018-03-05 19:18 ` Linus Torvalds
2018-02-21 22:52 ` Kees Cook
2018-02-21 23:24 ` Linus Torvalds
2018-02-22 0:12 ` Kees Cook
2018-02-22 0:22 ` Linus Torvalds
2018-02-22 0:23 ` Kees Cook
2018-02-22 0:27 ` Kees Cook
2017-11-11 1:13 ` [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11 J. Bruce Fields
2017-11-11 2:32 ` Al Viro
2017-11-10 1:47 ` Patrick McLean
2017-11-09 20:47 ` J. Bruce Fields
2017-11-09 23:07 ` Patrick McLean
2017-11-13 22:59 ` bit tweaks [was: Re: [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11] Rasmus Villemoes
2017-11-13 23:30 ` Linus Torvalds
2017-11-13 23:54 ` Linus Torvalds [this message]
2017-11-14 22:24 ` Rasmus Villemoes
2017-11-14 22:43 ` Linus Torvalds
2017-11-14 23:53 ` Rasmus Villemoes
2017-11-15 0:02 ` Linus Torvalds
2017-11-11 2:47 ` [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11 Alan Cox
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