powerpc/pmac: Don't add_timer() twice

If the interrupt and the timeout happen roughly at the same
time, we can get into a situation where the timer function
is run while the interrupt has already been processed. In
this case, the timer function might end up doing an add_timer
on an already pending timer, causing a BUG_ON() to trigger.

Instead, just skip the whole timeout operation if we see that
the timer is pending. The spinlock ensures that the only way
that happens is if we already started a new operation and thus
the timeout can be ignored.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/powermac/low_i2c.c b/arch/powerpc/platforms/powermac/low_i2c.c
index 996c5ff7824b..03685a329d7d 100644
--- a/arch/powerpc/platforms/powermac/low_i2c.c
+++ b/arch/powerpc/platforms/powermac/low_i2c.c
@@ -366,11 +366,20 @@ static void kw_i2c_timeout(unsigned long data)
         unsigned long flags;
 
         spin_lock_irqsave(&host->lock, flags);
+
+        /*
+         * If the timer is pending, that means we raced with the
+         * irq, in which case we just return
+         */
+        if (timer_pending(&host->timeout_timer))
+                goto skip;
+
         kw_i2c_handle_interrupt(host, kw_read_reg(reg_isr));
         if (host->state != state_idle) {
                 host->timeout_timer.expires = jiffies + KW_POLL_TIMEOUT;
                 add_timer(&host->timeout_timer);
         }
+ skip:
         spin_unlock_irqrestore(&host->lock, flags);
 }