genirq: Fix type of shifting literal 1 in __setup_irq()

If ffz() ever returns a value >= 31 then the following shift is undefined
behaviour because the literal 1 which gets shifted is treated as signed
integer.

In practice, the bug is probably harmless, since the first undefined shift
count is 31 which results - ignoring UB - in (int)(0x80000000). This gets
sign extended so bit 32-63 will be set as well and all subsequent
__setup_irq() calls would just end up hitting the -EBUSY branch.

However, a sufficiently aggressive optimizer may use the UB of 1<<31
to decide that doesn't happen, and hence elide the sign-extension
code, so that subsequent calls can indeed get ffz > 31.

In any case, the right thing to do is to make the literal 1UL.

[ tglx: For this to happen a single interrupt would have to be shared by 32
  	devices. Hardware like that does not exist and would have way more
  	problems than that. ]

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20171030213548.16831-1-linux@rasmusvillemoes.dk

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index c65f282..6a1bf9d 100644 (file)
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1289,7 +1289,7 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
                 * thread_mask assigned. See the loop above which or's
                 * all existing action->thread_mask bits.
                 */
-               new->thread_mask = 1 << ffz(thread_mask);
+               new->thread_mask = 1UL << ffz(thread_mask);
 
        } else if (new->handler == irq_default_primary_handler &&
                   !(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) {