From: Will Deacon <will.deacon@arm.com>
To: xinhui <xinhui.pan@linux.vnet.ibm.com>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
arnd@arndb.de, waiman.long@hp.com, peterz@infradead.org
Subject: Re: [PATCH] locking/qrwlock: fix write unlock issue in big endian
Date: Tue, 14 Jun 2016 11:40:33 +0100 [thread overview]
Message-ID: <20160614104032.GE19407@arm.com> (raw)
In-Reply-To: <575FA024.7060608@linux.vnet.ibm.com>
On Tue, Jun 14, 2016 at 02:11:48PM +0800, xinhui wrote:
>
> On 2016年06月08日 17:22, Will Deacon wrote:
> >On Thu, Jun 02, 2016 at 06:09:08PM +0800, Pan Xinhui wrote:
> >>strcut __qrwlock has different layout in big endian machine. we need set
> >>the __qrwlock->wmode to NULL, and the address is not &lock->cnts in big
> >>endian machine.
> >>
> >>Do as what read unlock does. we are lucky that the __qrwlock->wmode's
> >>val is _QW_LOCKED.
> >
> >Doesn't this have wider implications for the qrwlocks, for example:
> >
> > while ((cnts & _QW_WMASK) == _QW_LOCKED) { ... }
> >
> >would actually end up looking at the wrong field of the lock?
> >
> I does not clearly understand your idea. :(
That's because I'm talking rubbish :) Sorry, I completely confused myself.
Locking is bad enough on its own, but add big-endian to the mix and I'm
all done.
> >Shouldn't we just remove the #ifdef __LITTLE_ENDIAN stuff from __qrwlock,
> >given that all the struct members are u8?
> >
> No. that makes codes complex. for example
>
> struct __qrwlock lock;
>
> WRITE_ONCE(lock->wmode, _QW_WAITING);
> if (atomic_(&lock->cnts) == _QW_WAITING) {
> do_something();
> }
>
> IF you remove the #ifdef __LITTLE_ENDIAN stuff from __qrwlock.
> codes above obviously will break. And we already have such code.
I was wondering more along the lines of having one definition of the data
structure, but then defining _QW_* differently depending on endianness
(i.e. add a << 24 when big-endian). That way queued_write_unlock can
stay like it is (having an arch override to handle the big-endian case
is incredibly ugly).
Will
next prev parent reply other threads:[~2016-06-14 10:40 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-02 10:09 [PATCH] locking/qrwlock: fix write unlock issue in big endian Pan Xinhui
2016-06-02 10:44 ` Arnd Bergmann
2016-06-02 11:01 ` xinhui
2016-06-02 11:15 ` Peter Zijlstra
2016-06-03 7:20 ` xinhui
2016-06-02 11:02 ` Peter Zijlstra
2016-06-03 7:17 ` xinhui
[not found] ` <201606030718.u537FQg0009963@mx0a-001b2d01.pphosted.com>
2016-06-03 20:57 ` Waiman Long
2016-06-06 3:15 ` xinhui
2016-06-08 9:22 ` Will Deacon
2016-06-14 6:11 ` xinhui
2016-06-14 10:40 ` Will Deacon [this message]
2016-06-15 3:47 ` xinhui
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=20160614104032.GE19407@arm.com \
--to=will.deacon@arm.com \
--cc=arnd@arndb.de \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=waiman.long@hp.com \
--cc=xinhui.pan@linux.vnet.ibm.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).