genirq: Prevent early spurious wake-ups of interrupt threads

genirq: Prevent early spurious wake-ups of interrupt threads

During initialization, the interrupt thread is created before the interrupt
is enabled. The interrupt enablement happens before the actual kthread wake
up point. Once the interrupt is enabled the hardware can raise an interrupt
and once setup_irq() drops the descriptor lock a interrupt wake-up can
happen.

Even when such an interrupt can be considered premature, this is not a
problem in general because at the point where the descriptor lock is
dropped and the wakeup can happen, the data which is used by the thread is
fully initialized.

Though from the perspective of least surprise, the initial wakeup really
should be performed by the setup code and not randomly by a premature
interrupt.

Prevent this by performing a wake-up only if the target is in state
TASK_INTERRUPTIBLE, which the thread uses in wait_for_interrupt().

If the thread is still in state TASK_UNINTERRUPTIBLE, the wake-up is not
lost because after the setup code completed the initial wake-up the thread
will observe the IRQTF_RUNTHREAD and proceed with the handling.

[ tglx: Simplified the changes and extended the changelog. ]

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251121143500.42111-2-frederic@kernel.org