1. 24 Mar, 2010 1 commit
  2. 10 Mar, 2010 1 commit
    • Thomas Gleixner's avatar
      genirq: Prevent oneshot irq thread race · 0b1adaa0
      Thomas Gleixner authored
      Lars-Peter pointed out that the oneshot threaded interrupt handler
      code has the following race:
      
       CPU0                            CPU1
       hande_level_irq(irq X)
         mask_ack_irq(irq X)
         handle_IRQ_event(irq X)
           wake_up(thread_handler)
                                       thread handler(irq X) runs
                                       finalize_oneshot(irq X)
      				  does not unmask due to 
      				  !(desc->status & IRQ_MASKED)
      
       return from irq
       does not unmask due to
       (desc->status & IRQ_ONESHOT)
        				  
      This leaves the interrupt line masked forever. 
      
      The reason for this is the inconsistent handling of the IRQ_MASKED
      flag. Instead of setting it in the mask function the oneshot support
      sets the flag after waking up the irq thread.
      
      The solution for this is to set/clear the IRQ_MASKED status whenever
      we mask/unmask an interrupt line. That's the easy part, but that
      cleanup opens another race:
      
       CPU0                            CPU1
       hande_level_irq(irq)
         mask_ack_irq(irq)
         handle_IRQ_event(irq)
           wake_up(thread_handler)
                                       thread handler(irq) runs
                                       finalize_oneshot_irq(irq)
      				  unmask(irq)
           irq triggers again
           handle_level_irq(irq)
             mask_ack_irq(irq)
           return from irq due to IRQ_INPROGRESS				  
      
       return from irq
       does not unmask due to
       (desc->status & IRQ_ONESHOT)
      
      This requires that we synchronize finalize_oneshot_irq() with the
      primary handler. If IRQ_INPROGESS is set we wait until the primary
      handler on the other CPU has returned before unmasking the interrupt
      line again.
      
      We probably have never seen that problem because it does not happen on
      UP and on SMP the irqbalancer protects us by pinning the primary
      handler and the thread to the same CPU.
      Reported-by: default avatarLars-Peter Clausen <lars@metafoo.de>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: stable@kernel.org
      0b1adaa0
  3. 09 Mar, 2010 1 commit
  4. 08 Mar, 2010 37 commits