linux-kernel - [PATCH] of/unittest: fix infinite loop in of_unittest_destroy_tracked

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Date:	Wed,  2 Mar 2016 20:24:49 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Rob Herring <robh+dt@...nel.org>
Cc:	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Petr Mladek <pmladek@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [PATCH] of/unittest: fix infinite loop in of_unittest_destroy_tracked_overlays()

of_overlay_destroy() can return `-ENODEV' error code once it
failed to find the requested overlay in `ov_idr'. However,
of_unittest_destroy_tracked_overlays() does not handle this
error code correctly and continues to call of_overlay_destroy()
on the 'missing' overlay over and over again. This results in
a printk flood

[..]
[   33.497583] of_overlay_destroy: Could not find overlay #6
[   33.497583] of_overlay_destroy: Could not find overlay #6
[   33.497584] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[   33.497584] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[   33.497586] of_overlay_destroy: Could not find overlay #6
[   33.497586] of_overlay_destroy: Could not find overlay #6
[   33.497587] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[   33.497587] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[..]

which is not really good due to printk design, and can lead to soft
lockups, hard lockups, etc. (depending on the context console_unlock()
is being called from). The problem has bee observed in real life
and reported by Ying Huang.

This patch does not address the root cause of missing overlay in
`ov_idr', it fixes the endless loop only.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Reported-by: kernel test robot <ying.huang@...ux.intel.com>
Link: lkml.kernel.org/r/87fuwk1c0o.fsf@...ang-dev.intel.com
---
 drivers/of/unittest.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 979b6e4..e986e6e 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -1165,6 +1165,11 @@ static void of_unittest_destroy_tracked_overlays(void)
 				continue;
 
 			ret = of_overlay_destroy(id + overlay_first_id);
+			if (ret == -ENODEV) {
+				pr_warn("%s: no overlay to destroy for #%d\n",
+					__func__, id + overlay_first_id);
+				continue;
+			}
 			if (ret != 0) {
 				defers++;
 				pr_warn("%s: overlay destroy failed for #%d\n",
-- 
2.8.0.rc0