iwlwifi: fix PCI-E transport "inta" race

When an interrupt comes in, we read the reason
bits and collect them into "trans_pcie->inta".
This happens with the spinlock held. However,
there's a bug resetting this variable -- that
happens after the spinlock has been released.
This means that it is possible for interrupts
to be missed if the reset happens after some
other interrupt reasons were already added to
the variable.

I found this by code inspection, looking for a
reason that we sometimes see random commands
time out. It seems possible that this causes
such behaviour, but I can't say for sure right
now since it happens extremely infrequently on
my test systems.

Cc: stable@vger.kernel.org [3.2]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c b/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
index 752493f00406a0a808c0984d0ddc96b215ce3fb1..65d1f05007be0e0b6ba421e24b273b3bb77adc97 100644 (file)
--- a/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
@@ -972,11 +972,11 @@ void iwl_irq_tasklet(struct iwl_trans *trans)
        }
 #endif
 
-       spin_unlock_irqrestore(&trans->shrd->lock, flags);
-
        /* saved interrupt in inta variable now we can reset trans_pcie->inta */
        trans_pcie->inta = 0;
 
+       spin_unlock_irqrestore(&trans->shrd->lock, flags);
+
        /* Now service all interrupt bits discovered above. */
        if (inta & CSR_INT_BIT_HW_ERR) {
                IWL_ERR(trans, "Hardware error detected.  Restarting.\n");