On Mon, Jul 18, 2016 at 05:47:39PM +0800, Pan Xinhui wrote:
> From: pan xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
>
> This patch aims to get rid of endianness in queued_write_unlock(). We
> want to set __qrwlock->wmode to NULL, however the address is not
> &lock->cnts in big endian machine. That causes queued_write_unlock()
> write NULL to the wrong field of __qrwlock.
>
> So implement __qrwlock_write_byte() which returns the correct
> __qrwlock->wmode address.
>
> Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
> ---
> change from v3:
> rewrite totally. :)
> change from v2:
> change macro's name, add comments.
> change from v1:
> A typo fix which is really bad...
> thanks Will for the carefull review.
> ---
> include/asm-generic/qrwlock.h | 27 +++++++++++++++++++++++++--
> 1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> index 54a8e65..7d026bf 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -25,7 +25,20 @@
> #include <asm-generic/qrwlock_types.h>
>
> /*
> - * Writer states & reader shift and bias
> + * Writer states & reader shift and bias.
> + *
> + * | +0 | +1 | +2 | +3 |
> + * ----+----+----+----+----+
> + * LE | 78 | 56 | 34 | 12 | 0x12345678
> + * ----+----+----+----+----+
> + * | wr | rd |
> + * +----+----+----+----+
> + *
> + * ----+----+----+----+----+
> + * BE | 12 | 34 | 56 | 78 | 0x12345678
> + * ----+----+----+----+----+
> + * | rd | wr |
> + * +----+----+----+----+
> */
> #define _QW_WAITING 1 /* A writer is waiting */
> #define _QW_LOCKED 0xff /* A writer holds the lock */
> @@ -134,12 +147,22 @@ static inline void queued_read_unlock(struct qrwlock *lock)
> }
>
> /**
> + * __qrwlock_write_byte - retrieve the write byte address of a queue rwlock
> + * @lock : Pointer to queue rwlock structure
> + * Return: the write byte address of a queue rwlock
> + */
> +static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
> +{
> + return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
> +}
Might be worth a comment here, saying that IS_BUILTIN expands to 1 or 0.
Either way, the patch looks correct to me:
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Will
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