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powerpc/pseries: Duplicate dtl entries sometimes sent to userspace

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

# hexdump -C dtl.out

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@samba.org>
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2013-11-17 11:39:05 +11:00 committed by Benjamin Herrenschmidt
parent 9db8bcfd73
commit 84b073868b
1 changed files with 2 additions and 2 deletions
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4
arch/powerpc/kernel/time.c
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@ -213,8 +213,6 @@ static u64 scan_dispatch_log(u64 stop_tb)
if (i == be64_to_cpu(vpa->dtl_idx))
return 0;
while (i < be64_to_cpu(vpa->dtl_idx)) {
if (dtl_consumer)
dtl_consumer(dtl, i);
dtb = be64_to_cpu(dtl->timebase);
tb_delta = be32_to_cpu(dtl->enqueue_to_dispatch_time) +
be32_to_cpu(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;