Patch "kernel/resource.c: fix muxed resource handling in __request_region()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

kernel/resource.c: fix muxed resource handling in __request_region()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kernel-resource.c-fix-muxed-resource-handling-in-__request_region.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Simon Guinot <[email protected]>
Date: Thu, 10 Sep 2015 00:15:18 +0200
Subject: kernel/resource.c: fix muxed resource handling in __request_region()

From: Simon Guinot <[email protected]>

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.

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

@@ -1083,9 +1083,10 @@ 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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/kernel-resource.c-fix-muxed-resource-handling-in-__request_region.patch