[PATCH v3 01/10] x86/mce/dev-mcelog: Use xchg() to get and clear the flags

[Qiuxu Zhuo]

Using xchg() to atomically get and clear the MCE log buffer flags,
streamlines the code and reduces the text size by 20 bytes.

  $ size dev-mcelog.o.*

       text	   data	    bss	    dec	    hex	filename
       3013	    360	    160	   3533	    dcd	dev-mcelog.o.old
       2993	    360	    160	   3513	    db9	dev-mcelog.o.new

No functional changes intended.

Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
Reviewed-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
---
Changes in v3:
  - Collect "Reviewed-by:" from Nikolay & Sohil.

Changes in v2:
  - Collect "Reviewed-by:" from Tony.

 arch/x86/kernel/cpu/mce/dev-mcelog.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/dev-mcelog.c b/arch/x86/kernel/cpu/mce/dev-mcelog.c
index af44fd5dbd7c..8d023239ce18 100644
--- a/arch/x86/kernel/cpu/mce/dev-mcelog.c
+++ b/arch/x86/kernel/cpu/mce/dev-mcelog.c
@@ -264,15 +264,8 @@ static long mce_chrdev_ioctl(struct file *f, unsigned int cmd,
 		return put_user(sizeof(struct mce), p);
 	case MCE_GET_LOG_LEN:
 		return put_user(mcelog->len, p);
-	case MCE_GETCLEAR_FLAGS: {
-		unsigned flags;
-
-		do {
-			flags = mcelog->flags;
-		} while (cmpxchg(&mcelog->flags, flags, 0) != flags);
-
-		return put_user(flags, p);
-	}
+	case MCE_GETCLEAR_FLAGS:
+		return put_user(xchg(&mcelog->flags, 0), p);
 	default:
 		return -ENOTTY;
 	}
-- 
2.17.1