[PATCH 3.2 32/62] kernel/resource.c: fix muxed resource handling in __request_region()

From: Ben Hutchings
Date: Tue Mar 29 2016 - 16:11:29 EST

3.2.79-rc1 review patch. If anyone has any objections, please let me know.


From: Simon Guinot <simon.guinot@xxxxxxxxxxxx>

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

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@xxxxxxxxx>
Signed-off-by: Simon Guinot <simon.guinot@xxxxxxxxxxxx>
Tested-by: Vincent Donnefort <vdonnefort@xxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
kernel/resource.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -886,9 +886,10 @@ struct resource * __request_region(struc
if (!conflict)
if (conflict != parent) {
- parent = conflict;
- if (!(conflict->flags & IORESOURCE_BUSY))
+ if (!(conflict->flags & IORESOURCE_BUSY)) {
+ parent = conflict;
+ }
if (conflict->flags & flags & IORESOURCE_MUXED) {
add_wait_queue(&muxed_resource_wait, &wait);