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Message-ID: <20200330233020.GF19865@paulmck-ThinkPad-P72>
Date: Mon, 30 Mar 2020 16:30:20 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>,
Maddie Stone <maddiestone@...gle.com>,
Marco Elver <elver@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com,
kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH 09/21] list: Remove unnecessary WRITE_ONCE() from
hlist_bl_add_before()
On Tue, Mar 24, 2020 at 03:36:31PM +0000, Will Deacon wrote:
> There is no need to use WRITE_ONCE() when inserting into a non-RCU
> protected list.
>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Will Deacon <will@...nel.org>
OK, I will bite... Why "unsigned long" instead of "uintptr_t"?
Not that it matters in the context of the Linux kernel, so:
Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Thanx, Paul
> ---
> include/linux/list_bl.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
> index 1804fdb84dda..c93e7e3aa8fc 100644
> --- a/include/linux/list_bl.h
> +++ b/include/linux/list_bl.h
> @@ -91,15 +91,15 @@ static inline void hlist_bl_add_before(struct hlist_bl_node *n,
> struct hlist_bl_node *next)
> {
> struct hlist_bl_node **pprev = next->pprev;
> + unsigned long val;
>
> n->pprev = pprev;
> n->next = next;
> next->pprev = &n->next;
>
> /* pprev may be `first`, so be careful not to lose the lock bit */
> - WRITE_ONCE(*pprev,
> - (struct hlist_bl_node *)
> - ((uintptr_t)n | ((uintptr_t)*pprev & LIST_BL_LOCKMASK)));
> + val = (unsigned long)n | ((unsigned long)*pprev & LIST_BL_LOCKMASK);
> + *pprev = (struct hlist_bl_node *)val;
> }
>
> static inline void hlist_bl_add_behind(struct hlist_bl_node *n,
> --
> 2.20.1
>
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