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    Subject[PATCH review for 4.4 25/26] genirq: Clarify logic calculating bogus irqreturn_t values
    Date
    From: Jeremy Kerr <jk@ozlabs.org>

    [ Upstream commit 5d4bac9a5f4ef24b2482529bda6661a58e5b5b65 ]

    Although irqreturn_t is an enum, we treat it (and its enumeration
    constants) as a bitmask.

    However, bad_action_ret() uses a less-than operator to determine whether
    an irqreturn_t falls within allowable bit values, which means we need to
    know the signededness of an enum type to read the logic, which is
    implementation-dependent.

    This change explicitly uses an unsigned type for the comparison. We do
    this instead of changing to a bitwise test, as the latter compiles to
    increased instructions in this hot path.

    It looks like we get the correct behaviour currently (bad_action_ret(-1)
    returns 1), so this is purely a readability fix.

    Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
    Link: http://lkml.kernel.org/r/1487219049-4061-1-git-send-email-jk@ozlabs.org
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    ---
    kernel/irq/spurious.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
    index 32144175458d..fac1ad4db9d6 100644
    --- a/kernel/irq/spurious.c
    +++ b/kernel/irq/spurious.c
    @@ -175,7 +175,9 @@ out:

    static inline int bad_action_ret(irqreturn_t action_ret)
    {
    - if (likely(action_ret <= (IRQ_HANDLED | IRQ_WAKE_THREAD)))
    + unsigned int r = action_ret;
    +
    + if (likely(r <= (IRQ_HANDLED | IRQ_WAKE_THREAD)))
    return 0;
    return 1;
    }
    --
    2.11.0
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