sfc: Do not use efx_process_channel_now() in online self-test

During self-tests we use efx_process_channel_now() to handle
completion and other events synchronously.  This disables interrupts
and NAPI processing for the channel in question, but it may still be
interrupted by another channel.  A single socket may receive packets
from multiple net devices or even multiple channels of the same net
device, so this can result in deadlock on a socket lock.

Receiving packets in process context will also result in incorrect
classification by the network cgroup classifier.

Therefore, we must only use efx_process_channel_now() in the offline
loopback tests (which never deliver packets up the stack) and not for
the online interrupt and event tests.

For the interrupt test, there is no reason to process events.  We
only care that an interrupt is raised.

For the event test, we want to know whether events have been received,
and there may be many events ahead of the one we inject.  Therefore
remove efx_channel::magic_count and instead test whether
efx_channel::eventq_read_ptr advances.  This is currently an event
queue index and might wrap around to exactly the same value, resulting
in a false negative.  Therefore move the masking to efx_event() and
efx_nic_eventq_read_ack() so that it cannot wrap within the time of
the test.

The event test also tries to diagnose failures by checking whether an
event was delivered without causing an interrupt.  Add and use a
helper function that only does this.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/net/sfc/efx.c b/drivers/net/sfc/efx.c
index 0dc800b5a4ea..a3c2aab53de8 100644
--- a/drivers/net/sfc/efx.c
+++ b/drivers/net/sfc/efx.c
@@ -328,7 +328,8 @@ static int efx_poll(struct napi_struct *napi, int budget)
  * processing to finish, then directly poll (and ack ) the eventq.
  * Finally reenable NAPI and interrupts.
  *
- * Since we are touching interrupts the caller should hold the suspend lock
+ * This is for use only during a loopback self-test.  It must not
+ * deliver any packets up the stack as this can result in deadlock.
  */
 void efx_process_channel_now(struct efx_channel *channel)
 {
@@ -336,6 +337,7 @@ void efx_process_channel_now(struct efx_channel *channel)
 
 	BUG_ON(channel->channel >= efx->n_channels);
 	BUG_ON(!channel->enabled);
+	BUG_ON(!efx->loopback_selftest);
 
 	/* Disable interrupts and wait for ISRs to complete */
 	efx_nic_disable_interrupts(efx);