From: Nick Desaulniers <ndesaulniers@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Nicolas Pitre" <nicolas.pitre@linaro.org>,
linux-mips@linux-mips.org, linux-sh@vger.kernel.org,
benh@kernel.crashing.org, "Will Deacon" <will.deacon@arm.com>,
paulus@samba.org, mpe@ellerman.id.au, jejb@parisc-linux.org,
"Geert Uytterhoeven" <geert@linux-m68k.org>,
"Catalin Marinas" <catalin.marinas@arm.com>,
gor@linux.vnet.ibm.com, "Matt Turner" <mattst88@gmail.com>,
uclinux-h8-devel@lists.sourceforge.jp,
"Marc Zyngier" <marc.zyngier@arm.com>,
linuxram@us.ibm.com, linux-um@lists.infradead.org,
"Nicholas Piggin" <npiggin@gmail.com>,
luto@kernel.org, shannon.nelson@oracle.com,
"Thomas Gleixner" <tglx@linutronix.de>,
"Alex Bennée" <alex.bennee@linaro.org>,
rth@twiddle.net, jkosina@suse.cz,
LKML <linux-kernel@vger.kernel.org>,
ralf@linux-mips.org, rkuo@codeaurora.org, paul.burton@mips.com,
aneesh.kumar@linux.vnet.ibm.com,
"Greg KH" <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] treewide: remove current_text_addr
Date: Fri, 31 Aug 2018 09:48:56 -0700 [thread overview]
Message-ID: <CAKwvOdmXhRZJ5bQw+W0Ro+oeWSTRJzG1UAJnjyjciR1JFs+ubA@mail.gmail.com> (raw)
In-Reply-To: <4d1a8f35-e2fc-70d2-ca0e-44b8574c86f1@zytor.com>
On Mon, Aug 27, 2018 at 6:34 AM H. Peter Anvin <hpa@zytor.com> wrote:
>
> On 08/27/18 06:11, Peter Zijlstra wrote:
> > On Mon, Aug 27, 2018 at 05:26:53AM -0700, H. Peter Anvin wrote:
> >
> >> _THIS_IP_, however, is completely ill-defined, other than being an
> >> address *somewhere* in the same global function (not even necessarily
> >> the same function if the function is static!) As my experiment show, in
> >> many (nearly) cases gcc will hoist the address all the way to the top of
> >> the function, at least for the current generic implementation.
> >
> > It seems to have mostly worked so far... did anything change?
> >
>
> Most likely because the major architectures contain a arch-specific
> assembly implementation. The generic implementation used in some places
> is completely broken, as my experiments show.
>
> >> For the case where _THIS_IP_ is passed to an out-of-line function in all
> >> cases, it is extra pointless because all it does is increase the
> >> footprint of every caller: _RET_IP_ is inherently passed to the function
> >> anyway, and with tailcall protection it will uniquely identify a callsite.
> >
> > So I think we can convert many of the lockdep _THIS_IP_ calls to
> > _RET_IP_ on the other side, with a wee bit of care.
> >
> > A little something like so perhaps...
>
> I don't have time to look at this right now (I'm on sabbatical, and I'm
> dealing with personal legal stuff right at the moment), but I think it
> is the right direction.
>
> -hpa
Linus,
Can this patch please be merged? Then we can polish off Peter's
change to lockdep to not even use _THIS_IP_.
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2018-08-31 16:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAKwvOdkWL_2yTnJqM6n6R9UCPwY4iz-9BQYGN2MDAk9EzumUvA@mail.gmail.com>
[not found] ` <20180821202900.208417-1-ndesaulniers@google.com>
[not found] ` <207784db-4fcc-85e7-a0b2-fec26b7dab81@gmx.de>
2018-08-26 2:38 ` [PATCH] treewide: remove current_text_addr H. Peter Anvin
2018-08-26 3:16 ` H. Peter Anvin
2018-08-26 4:56 ` H. Peter Anvin
2018-08-26 19:30 ` H. Peter Anvin
2018-08-26 20:25 ` Linus Torvalds
2018-08-27 2:52 ` Nick Desaulniers
2018-08-27 7:33 ` Peter Zijlstra
2018-08-27 12:26 ` H. Peter Anvin
2018-08-27 13:11 ` Peter Zijlstra
2018-08-27 13:33 ` H. Peter Anvin
2018-08-31 16:48 ` Nick Desaulniers [this message]
2018-08-27 7:43 ` Nicholas Piggin
2018-08-26 23:20 ` H. Peter Anvin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKwvOdmXhRZJ5bQw+W0Ro+oeWSTRJzG1UAJnjyjciR1JFs+ubA@mail.gmail.com \
--to=ndesaulniers@google.com \
--cc=alex.bennee@linaro.org \
--cc=aneesh.kumar@linux.vnet.ibm.com \
--cc=benh@kernel.crashing.org \
--cc=catalin.marinas@arm.com \
--cc=geert@linux-m68k.org \
--cc=gor@linux.vnet.ibm.com \
--cc=gregkh@linuxfoundation.org \
--cc=jejb@parisc-linux.org \
--cc=jkosina@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@linux-mips.org \
--cc=linux-sh@vger.kernel.org \
--cc=linux-um@lists.infradead.org \
--cc=linuxram@us.ibm.com \
--cc=luto@kernel.org \
--cc=marc.zyngier@arm.com \
--cc=mattst88@gmail.com \
--cc=mpe@ellerman.id.au \
--cc=nicolas.pitre@linaro.org \
--cc=npiggin@gmail.com \
--cc=paul.burton@mips.com \
--cc=paulus@samba.org \
--cc=ralf@linux-mips.org \
--cc=rkuo@codeaurora.org \
--cc=rth@twiddle.net \
--cc=shannon.nelson@oracle.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=uclinux-h8-devel@lists.sourceforge.jp \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).