From: Jeff Dike The spurious IRQ testing in request_irq is mishandled in um_request_irq, which sets the incoming file descriptors non-blocking only after request_irq succeeds. This results in the spurious irq calling read on a blocking descriptor, and a hang. Fixed by reversing the O_NONBLOCK setting and the request_irq call. Signed-off-by: Jeff Dike Signed-off-by: Andrew Morton --- arch/um/kernel/irq.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff -puN arch/um/kernel/irq.c~uml-fix-spurious-irq-testing arch/um/kernel/irq.c --- a/arch/um/kernel/irq.c~uml-fix-spurious-irq-testing +++ a/arch/um/kernel/irq.c @@ -347,14 +347,15 @@ int um_request_irq(unsigned int irq, int { int err; - err = request_irq(irq, handler, irqflags, devname, dev_id); - if (err) - return err; - - if (fd != -1) + if (fd != -1) { err = activate_fd(irq, fd, type, dev_id); - return err; + if (err) + return err; + } + + return request_irq(irq, handler, irqflags, devname, dev_id); } + EXPORT_SYMBOL(um_request_irq); EXPORT_SYMBOL(reactivate_fd); _