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    Subject[PATCH 3.13.y-ckt 105/138] kernel/resource.c: fix muxed resource handling in __request_region()
    Date
    3.13.11-ckt36 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Simon Guinot <simon.guinot@sequanux.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@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: Kamal Mostafa <kamal@canonical.com>
    ---
    kernel/resource.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/kernel/resource.c b/kernel/resource.c
    index 3f285dc..449282e 100644
    --- a/kernel/resource.c
    +++ b/kernel/resource.c
    @@ -961,9 +961,10 @@ 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);
    --
    2.7.0
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