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

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@gmail.com>
Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
Tested-by: Vincent Donnefort <vdonnefort@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/kernel/resource.c b/kernel/resource.c
index 3c2237ac32dbedf56d10444a7feef59e6b35a561..db48bab5ea18b22e7f109b49111921838b2490f9 100644 (file)
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -957,9 +957,10 @@ 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);