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
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