iwlwifi: fix PCI-E transport "inta" race

commit b49ba04a3a0382e7314d990707c21094c410425a upstream.

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.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c b/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
index 1920237..1daf01e 100644 (file)
--- a/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
@@ -957,11 +957,11 @@ 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");