From a1d75dad3a2c689e70a1c4e0214cca9de741d0aa Mon Sep 17 00:00:00 2001
From: Zhi Jin <zhi.jin@intel.com>
Date: Thu, 6 Sep 2018 15:22:10 +0800
Subject: [PATCH] stm class: Fix an endless loop in channel allocation
Git-commit: a1d75dad3a2c689e70a1c4e0214cca9de741d0aa
Patch-mainline: v5.1-rc1
References: bsc#1051510

There is a bug in the channel allocation logic that leads to an endless
loop when looking for a contiguous range of channels in a range with a
mixture of free and occupied channels. For example, opening three
consequtive channels, closing the first two and requesting 4 channels in
a row will trigger this soft lockup. The bug is that the search loop
forgets to skip over the range once it detects that one channel in that
range is occupied.

Restore the original intent to the logic by fixing the omission.

Signed-off-by: Zhi Jin <zhi.jin@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Fixes: 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace Module devices")
Cc: stable@vger.kernel.org # v4.4+
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/hwtracing/stm/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 93ce3aa740a9..c80b064224f6 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -244,6 +244,9 @@ static int find_free_channels(unsigned long *bitmap, unsigned int start,
 			;
 		if (i == width)
 			return pos;
+
+		/* step over [pos..pos+i) to continue search */
+		pos += i;
 	}
 
 	return -1;
-- 
2.16.4