[PATCH net] net: usb: aqc111: Do not perform PM inside runtime suspend callback

["Nikola Z. Ivanov" <zlatistiv@gmail.com>]

syzbot reports "task hung in rpm_resume"

This is caused by aqc111_suspend calling
the PM variant of its write_cmd routine.

The simplified call trace looks like this:

rpm_suspend()
  usb_suspend_both() - here udev->dev.power.runtime_status == RPM_SUSPENDING
    aqc111_suspend() - called for the usb device interface
      aqc111_write32_cmd()
        usb_autopm_get_interface()
          pm_runtime_resume_and_get()
            rpm_resume() - here we call rpm_resume() on our parent
              rpm_resume() - Here we wait for a status change that will never happen.

At this point we block another task which holds
rtnl_lock and locks up the whole networking stack.

Fix this by replacing the write_cmd calls with their _nopm variants
in the case where we are inside a runtime suspend call.

Reported-by: syzbot+48dc1e8dfc92faf1124c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=48dc1e8dfc92faf1124c
Fixes: e58ba4544c77 ("net: usb: aqc111: Add support for wake on LAN by MAGIC packet")
Signed-off-by: Nikola Z. Ivanov <zlatistiv@gmail.com>
---
This patch is untested!
I do not have access to a real device to test it,
testing on real hardware would be appreciated,
if anyone has a device laying around.

I have found no reason for the PM variants to be
used in the ->suspend callback when it comes
to the device driver.

The PM docs suggest that PM should not be done
during runtime suspend, but I cannot find a
definitive answer for system suspend, hence the
conditional if(PMSG_IS_AUTO(message))

 drivers/net/usb/aqc111.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/aqc111.c b/drivers/net/usb/aqc111.c
index cbffa9ae1bb6..2f0d66c7ade0 100644
--- a/drivers/net/usb/aqc111.c
+++ b/drivers/net/usb/aqc111.c
@@ -1395,14 +1395,27 @@ static int aqc111_suspend(struct usb_interface *intf, pm_message_t message)
 		aqc111_write16_cmd_nopm(dev, AQ_ACCESS_MAC,
 					SFR_MEDIUM_STATUS_MODE, 2, &reg16);
 
-		aqc111_write_cmd(dev, AQ_WOL_CFG, 0, 0,
-				 WOL_CFG_SIZE, &wol_cfg);
-		aqc111_write32_cmd(dev, AQ_PHY_OPS, 0, 0,
-				   &aqc111_data->phy_cfg);
+		if (PMSG_IS_AUTO(message)) {
+			aqc111_write_cmd_nopm(dev, AQ_WOL_CFG, 0, 0,
+					      WOL_CFG_SIZE, &wol_cfg);
+			aqc111_write32_cmd_nopm(dev, AQ_PHY_OPS, 0, 0,
+						&aqc111_data->phy_cfg);
+		} else {
+			aqc111_write_cmd(dev, AQ_WOL_CFG, 0, 0,
+					 WOL_CFG_SIZE, &wol_cfg);
+			aqc111_write32_cmd(dev, AQ_PHY_OPS, 0, 0,
+					   &aqc111_data->phy_cfg);
+		}
 	} else {
 		aqc111_data->phy_cfg |= AQ_LOW_POWER;
-		aqc111_write32_cmd(dev, AQ_PHY_OPS, 0, 0,
-				   &aqc111_data->phy_cfg);
+
+		if (PMSG_IS_AUTO(message)) {
+			aqc111_write32_cmd_nopm(dev, AQ_PHY_OPS, 0, 0,
+						&aqc111_data->phy_cfg);
+		} else {
+			aqc111_write32_cmd(dev, AQ_PHY_OPS, 0, 0,
+					   &aqc111_data->phy_cfg);
+		}
 
 		/* Disable RX path */
 		aqc111_read16_cmd_nopm(dev, AQ_ACCESS_MAC,
-- 
2.53.0