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

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@gmail.com>
Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
Tested-by: Vincent Donnefort <vdonnefort@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/kernel/resource.c b/kernel/resource.c
index 09c0597840b0..3669d1bfc425 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1083,9 +1083,10 @@ struct resource * __request_region(struct resource *parent,
                 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);