[patch] __do_IRQ does not check IRQ_DISABLED when IRQ_PER_CPU is set
In __do_IRQ(), the normal case is that IRQ_DISABLED is checked and if
set the handler (handle_IRQ_event()) is not called.
Earlier in __do_IRQ(), if IRQ_PER_CPU is set the code does not check
IRQ_DISABLED and calls the handler even though IRQ_DISABLED is set.
This behavior seems unintentional.
One user encountering this behavior is the CPE handler (in
arch/ia64/kernel/mca.c). When the CPE handler encounters too many
CPEs (such as a solid single bit error), it sets up a polling timer
and disables the CPE interrupt (to avoid excessive overhead logging
the stream of single bit errors). disable_irq_nosync() is called
which sets IRQ_DISABLED. The IRQ_PER_CPU flag was previously set
(in ia64_mca_late_init()). The net result is the CPE handler gets
called even though it is marked disabled.
If the behavior of not checking IRQ_DISABLED when IRQ_PER_CPU is
set is intentional, it would be worthy of a comment describing
the intended behavior. disable_irq_nosync() does call chip->disable()
to provide a chipset specifiec interface for disabling the interrupt,
which avoids this issue when used.
Comments???
Signed-off-by: Russ Anderson ([email protected])
--------------------------------------------------------------------
---
kernel/irq/handle.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
Index: linus/kernel/irq/handle.c
===================================================================
--- linus.orig/kernel/irq/handle.c 2007-10-30 09:49:26.000000000 -0500
+++ linus/kernel/irq/handle.c 2007-10-30 10:23:52.436719688 -0500
@@ -178,9 +178,11 @@ fastcall unsigned int __do_IRQ(unsigned
*/
if (desc->chip->ack)
desc->chip->ack(irq);
- action_ret = handle_IRQ_event(irq, desc->action);
- if (!noirqdebug)
- note_interrupt(irq, desc, action_ret);
+ if (likely(!(desc->status & IRQ_DISABLED))) {
+ action_ret = handle_IRQ_event(irq, desc->action);
+ if (!noirqdebug)
+ note_interrupt(irq, desc, action_ret);
+ }
desc->chip->end(irq);
return 1;
}
--
Russ Anderson, OS RAS/Partitioning Project Lead
SGI - Silicon Graphics Inc [email protected]
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