linux-kernel - [PATCH 3.14 127/130] kernel/resource.c: fix muxed resource handling in __request

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Message-Id: <20160301234504.248241385@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:53:41 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>, Simon Guinot <simon.guinot@...uanux.org>,
	Vincent Donnefort <vdonnefort@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.14 127/130] kernel/resource.c: fix muxed resource handling in __request_region()

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Simon Guinot <simon.guinot@...uanux.org>

commit 59ceeaaf355fa0fb16558ef7c24413c804932ada upstream.

In __request_region, if a conflict with a BUSY and MUXED resource is
detected, then the caller goes to sleep and waits for the resource to be
released.  A pointer on the conflicting resource is kept.  At wake-up
this pointer is used as a parent to retry to request the region.

A first problem is that this pointer might well be invalid (if for
example the conflicting resource have already been freed).  Another
problem is that the next call to __request_region() fails to detect a
remaining conflict.  The previously conflicting resource is passed as a
parameter and __request_region() will look for a conflict among the
children of this resource and not at the resource itself.  It is likely
to succeed anyway, even if there is still a conflict.

Instead, the parent of the conflicting resource should be passed to
__request_region().

As a fix, this patch doesn't update the parent resource pointer in the
case we have to wait for a muxed region right after.

Reported-and-tested-by: Vincent Pelletier <plr.vincent@...il.com>
Signed-off-by: Simon Guinot <simon.guinot@...uanux.org>
Tested-by: Vincent Donnefort <vdonnefort@...il.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/resource.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -961,9 +961,10 @@ struct resource * __request_region(struc
 		if (!conflict)
 			break;
 		if (conflict != parent) {
-			parent = conflict;
-			if (!(conflict->flags & IORESOURCE_BUSY))
+			if (!(conflict->flags & IORESOURCE_BUSY)) {
+				parent = conflict;
 				continue;
+			}
 		}
 		if (conflict->flags & flags & IORESOURCE_MUXED) {
 			add_wait_queue(&muxed_resource_wait, &wait);