[3.5.y.z extended stable] Patch "powerpc/pseries: Duplicate dtl entries sometimes sent to userspace" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    powerpc/pseries: Duplicate dtl entries sometimes sent to userspace

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 3a794f008cd2182fa4c699e405e391deae62f858 Mon Sep 17 00:00:00 2001
From: Anton Blanchard <anton at samba.org>
Date: Sun, 17 Nov 2013 11:39:05 +1100
Subject: powerpc/pseries: Duplicate dtl entries sometimes sent to userspace

commit 84b073868b9d9e754ae48b828337633d1b386482 upstream.

When reading from the dispatch trace log (dtl) userspace interface, I
sometimes see duplicate entries. One example:

00000000  07 04 00 0c 00 00 48 44  00 00 00 00 00 00 00 00
00000010  00 0c a0 b4 16 83 6d 68  00 00 00 00 00 00 00 00
00000020  00 00 00 00 10 00 13 50  80 00 00 00 00 00 d0 32

00000030  07 04 00 0c 00 00 48 44  00 00 00 00 00 00 00 00
00000040  00 0c a0 b4 16 83 6d 68  00 00 00 00 00 00 00 00
00000050  00 00 00 00 10 00 13 50  80 00 00 00 00 00 d0 32

The problem is in scan_dispatch_log() where we call dtl_consumer()
but bail out before incrementing the index.

To fix this I moved dtl_consumer() after the timebase comparison.

Signed-off-by: Anton Blanchard <anton at samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/powerpc/kernel/time.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 3c50ed9..fe33f00 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -213,8 +213,6 @@ static u64 scan_dispatch_log(u64 stop_tb)
 	if (i == vpa->dtl_idx)
 		return 0;
 	while (i < vpa->dtl_idx) {
-		if (dtl_consumer)
-			dtl_consumer(dtl, i);
 		dtb = dtl->timebase;
 		tb_delta = dtl->enqueue_to_dispatch_time +
 			dtl->ready_to_enqueue_time;
@@ -227,6 +225,8 @@ static u64 scan_dispatch_log(u64 stop_tb)
 		}
 		if (dtb > stop_tb)
 			break;
+		if (dtl_consumer)
+			dtl_consumer(dtl, i);
 		stolen += tb_delta;
 		++i;
 		++dtl;
--
1.8.3.2