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authorThomas Gleixner <tglx@linutronix.de>2010-03-09 19:45:54 +0100
committerThomas Gleixner <tglx@linutronix.de>2010-03-10 17:45:14 +0100
commit0b1adaa031a55e44f5dd942f234bf09d28e8a0d6 (patch)
tree354aa6cbfbcd856226c543b9f263f87864245065 /kernel/irq
parent522dba7134d6b2e5821d3457f7941ec34f668e6d (diff)
downloadop-kernel-dev-0b1adaa031a55e44f5dd942f234bf09d28e8a0d6.zip
op-kernel-dev-0b1adaa031a55e44f5dd942f234bf09d28e8a0d6.tar.gz
genirq: Prevent oneshot irq thread race
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: Lars-Peter Clausen <lars@metafoo.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@kernel.org
Diffstat (limited to 'kernel/irq')
-rw-r--r--kernel/irq/chip.c31
-rw-r--r--kernel/irq/manage.c18
2 files changed, 40 insertions, 9 deletions
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index d70394f..71eba24 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -359,6 +359,23 @@ static inline void mask_ack_irq(struct irq_desc *desc, int irq)
if (desc->chip->ack)
desc->chip->ack(irq);
}
+ desc->status |= IRQ_MASKED;
+}
+
+static inline void mask_irq(struct irq_desc *desc, int irq)
+{
+ if (desc->chip->mask) {
+ desc->chip->mask(irq);
+ desc->status |= IRQ_MASKED;
+ }
+}
+
+static inline void unmask_irq(struct irq_desc *desc, int irq)
+{
+ if (desc->chip->unmask) {
+ desc->chip->unmask(irq);
+ desc->status &= ~IRQ_MASKED;
+ }
}
/*
@@ -484,10 +501,8 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
raw_spin_lock(&desc->lock);
desc->status &= ~IRQ_INPROGRESS;
- if (unlikely(desc->status & IRQ_ONESHOT))
- desc->status |= IRQ_MASKED;
- else if (!(desc->status & IRQ_DISABLED) && desc->chip->unmask)
- desc->chip->unmask(irq);
+ if (!(desc->status & (IRQ_DISABLED | IRQ_ONESHOT)))
+ unmask_irq(desc, irq);
out_unlock:
raw_spin_unlock(&desc->lock);
}
@@ -524,8 +539,7 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
action = desc->action;
if (unlikely(!action || (desc->status & IRQ_DISABLED))) {
desc->status |= IRQ_PENDING;
- if (desc->chip->mask)
- desc->chip->mask(irq);
+ mask_irq(desc, irq);
goto out;
}
@@ -593,7 +607,7 @@ handle_edge_irq(unsigned int irq, struct irq_desc *desc)
irqreturn_t action_ret;
if (unlikely(!action)) {
- desc->chip->mask(irq);
+ mask_irq(desc, irq);
goto out_unlock;
}
@@ -605,8 +619,7 @@ handle_edge_irq(unsigned int irq, struct irq_desc *desc)
if (unlikely((desc->status &
(IRQ_PENDING | IRQ_MASKED | IRQ_DISABLED)) ==
(IRQ_PENDING | IRQ_MASKED))) {
- desc->chip->unmask(irq);
- desc->status &= ~IRQ_MASKED;
+ unmask_irq(desc, irq);
}
desc->status &= ~IRQ_PENDING;
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index eb6078c..69a3d7b 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -483,8 +483,26 @@ static int irq_wait_for_interrupt(struct irqaction *action)
*/
static void irq_finalize_oneshot(unsigned int irq, struct irq_desc *desc)
{
+again:
chip_bus_lock(irq, desc);
raw_spin_lock_irq(&desc->lock);
+
+ /*
+ * Implausible though it may be we need to protect us against
+ * the following scenario:
+ *
+ * The thread is faster done than the hard interrupt handler
+ * on the other CPU. If we unmask the irq line then the
+ * interrupt can come in again and masks the line, leaves due
+ * to IRQ_INPROGRESS and the irq line is masked forever.
+ */
+ if (unlikely(desc->status & IRQ_INPROGRESS)) {
+ raw_spin_unlock_irq(&desc->lock);
+ chip_bus_sync_unlock(irq, desc);
+ cpu_relax();
+ goto again;
+ }
+
if (!(desc->status & IRQ_DISABLED) && (desc->status & IRQ_MASKED)) {
desc->status &= ~IRQ_MASKED;
desc->chip->unmask(irq);
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