Commit 3027691e authored Apr 18, 2012 by Benjamin Herrenschmidt

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>

parent 2ef822c5

arch/powerpc/platforms/powermac/low_i2c.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}