Messages in this thread | | | Subject | Re: [RFC PATCH v5 03/12] __wr_after_init: Core and default arch | From | Igor Stoppa <> | Date | Fri, 15 Feb 2019 01:10:33 +0200 |
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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
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