On Thu, 10 Mar 2016 01:16:57 +0100 Rasmus Villemoes <li...@rasmusvillemoes.dk>
wrote:
> Commit 7bd3e239d6c6 ("locking: Remove atomicy checks from
> {READ,WRITE}_ONCE") removed said warning.
>
> Acked-by: Christian Borntraeger <borntrae...@de.ibm.com>
> Signed-off-by: Rasmus Villemoes <li...@rasmusvillemoes.dk>
> ---
> Andrew, can you pick this up please?
>
> include/linux/compiler.h | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 48f5aab117ae..062b6ad95276 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -263,8 +263,7 @@ static __always_inline void __write_once_size(volatile
> void *p, void *res, int s
> * In contrast to ACCESS_ONCE these two macros will also work on aggregate
> * data types like structs or unions. If the size of the accessed data
> * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
> - * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
> - * compile-time warning.
> + * READ_ONCE() and WRITE_ONCE() will fall back to memcpy.
> *
> * Their two major use cases are: (1) Mediating communication between
> * process-level code and irq/NMI handlers, all running on the same CPU,
Conflicts with Konrad's patch in linux-next (from an IngoTree), below.
I'll drop your patch - Konrad covers the same info and more.
(grammar nazi: s/There's/There are/)
commit fed0764fafd8e2e629a033c0f7df4106b0dcb7f0
Author: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
AuthorDate: Mon Jan 25 16:33:20 2016 -0500
Commit: Ingo Molnar <mi...@kernel.org>
CommitDate: Tue Feb 9 14:50:16 2016 +0100
locking/atomics: Update comment about READ_ONCE() and structures
The comment is out of data. Also point out the performance drawback
of the barrier();__builtin_memcpy(); barrier() followed by another
copy from stack (__u) to lvalue;
Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Christian Borntraeger <borntrae...@de.ibm.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Sasha Levin <sasha.le...@oracle.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Link:
http://lkml.kernel.org/r/1453757600-11441-1-git-send-email-konrad.w...@oracle.com
[ Made it a bit more readable. ]
Signed-off-by: Ingo Molnar <mi...@kernel.org>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 00b042c..4291592 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -263,8 +263,9 @@ static __always_inline void __write_once_size(volatile void
*p, void *res, int s
* In contrast to ACCESS_ONCE these two macros will also work on aggregate
* data types like structs or unions. If the size of the accessed data
* type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
- * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
- * compile-time warning.
+ * READ_ONCE() and WRITE_ONCE() will fall back to memcpy(). There's at
+ * least two memcpy()s: one for the __builtin_memcpy() and then one for
+ * the macro doing the copy of variable - '__u' allocated on the stack.
*
* Their two major use cases are: (1) Mediating communication between
* process-level code and irq/NMI handlers, all running on the same CPU,
