From: Peter Zijlstra <peterz@infradead.org>
To: Mete Polat <metepolat2000@gmail.com>
Cc: Michel Lespinasse <michel@lespinasse.org>,
Davidlohr Bueso <dbueso@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Lukas Bulwahn <lukas.bulwahn@gmail.com>,
Jesper Nilsson <jesper@jni.nu>, Arnd Bergmann <arnd@arndb.de>,
David Woodhouse <dwmw2@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Randy Dunlap <rdunlap@infradead.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
kernel-janitors@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-m68k <linux-m68k@lists.linux-m68k.org>
Subject: Re: [PATCH v2] rbtree: remove unneeded explicit alignment in struct rb_node
Date: Fri, 6 Aug 2021 19:44:57 +0200 [thread overview]
Message-ID: <20210806174457.GA2184@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <YQ1ToK8EMdAO4CyH@precision>
On Fri, Aug 06, 2021 at 05:22:08PM +0200, Mete Polat wrote:
> Commit e977145aeaad ("[RBTREE] Add explicit alignment to sizeof(long) for
> struct rb_node.") adds an explicit alignment to the struct rb_node due to
> some speciality of the CRIS architecture.
>
> The support for the CRIS architecture was removed with commit c690eddc2f3b
> ("CRIS: Drop support for the CRIS port")
>
> So, remove this now unneeded explicit alignment in struct rb_node as well.
>
> This basically reverts commit e977145aeaad ("[RBTREE] Add explicit
> alignment to sizeof(long) for struct rb_node.").
>
> The rbtree node color is stored in the LSB of '__rb_parent_color'.
> Only mask the first bit in '__rb_parent()', otherwise it modifies the
> node's parent address on m68k.
I still don't believe for a second this will actually work. We rely on
rcu_assign_pointer() and rcu_dereference() to work on the
rb_{left,right} members, and I don't think any architecture can provide
single copy atomic loads and stores that are not naturally aligned (eg.
when they straddle a cache or page boundary).
next prev parent reply other threads:[~2021-08-06 17:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-06 15:22 [PATCH v2] rbtree: remove unneeded explicit alignment in struct rb_node Mete Polat
2021-08-06 17:44 ` Peter Zijlstra [this message]
2021-08-10 19:15 ` Mete Polat
2021-08-09 12:25 ` Geert Uytterhoeven
2021-08-10 19:39 ` Mete Polat
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