lkml.org 
[lkml]   [2019]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC PATCH v5 03/12] __wr_after_init: Core and default arch
From
Date


On 14/02/2019 13:28, Peter Zijlstra wrote:
> On Thu, Feb 14, 2019 at 12:41:32AM +0200, Igor Stoppa wrote:

[...]

>> +#define wr_rcu_assign_pointer(p, v) ({ \
>> + smp_mb(); \
>> + wr_assign(p, v); \
>> + p; \
>> +})
>
> This requires that wr_memcpy() (through wr_assign) is single-copy-atomic
> for native types. There is not a comment in sight that states this.

Right, I kinda expected native-aligned <-> atomic, but it's not
necessarily true. It should be confirmed when enabling write rare on a
new architecture. I'll add the comment.

> Also, is this true of x86/arm64 memcpy ?


For x86_64:
https://elixir.bootlin.com/linux/v5.0-rc6/source/arch/x86/include/asm/uaccess.h#L462
the mov"itype" part should deal with atomic copy of native, aligned
types.


For arm64:
https://elixir.bootlin.com/linux/v5.0-rc6/source/arch/arm64/lib/copy_template.S#L110
.Ltiny15 deals with copying less than 16 bytes, which includes pointers.
When the data is aligned, the copy of a pointer should be atomic.


--
igor

\
 
 \ /
  Last update: 2019-02-15 00:10    [W:1.408 / U:0.276 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site