If a interrupt chip utilizes chip->buslock then free_irq() can
deadlock in the following way:
CPU0 CPU1
interrupt(X) (Shared or spurious)
free_irq(X) interrupt_thread(X)
chip_bus_lock(X)
irq_finalize_oneshot(X)
chip_bus_lock(X)
synchronize_irq(X)
synchronize_irq() waits for the interrupt thread to complete,
i.e. forever.
Solution is simple: Drop chip_bus_lock() before calling
synchronize_irq() as we do with the irq_desc lock. There is nothing to
be protected after the point where irq_desc lock has been released.
This adds chip_bus_lock/unlock() to the remove_irq() code path, but
that's actually correct in the case where remove_irq() is called on
such an interrupt. The current users of remove_irq() are not affected
as none of those interrupts is on a chip which requires buslock.
Reported-by: Fredrik Markström <fredrik.markstrom@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
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