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
