On 09/06/2017 01:49 PM, David Daney wrote:
On 09/06/2017 11:59 AM, Florian Fainelli wrote:
On 09/06/2017 11:00 AM, David Daney wrote:
On 08/31/2017 11:29 AM, Florian Fainelli wrote:
On 08/31/2017 11:12 AM, Mason wrote:
On 31/08/2017 19:53, Florian Fainelli wrote:
On 08/31/2017 10:49 AM, Mason wrote:
On 31/08/2017 18:57, Florian Fainelli wrote:
And the race is between phy_detach() setting phydev->attached_dev
= NULL
and phy_state_machine() running in PHY_HALTED state and calling
netif_carrier_off().
I must be missing something.
(Since a thread cannot race against itself.)
phy_disconnect calls phy_stop_machine which
1) stops the work queue from running in a separate thread
2) calls phy_state_machine *synchronously*
which runs the PHY_HALTED case with everything well-defined
end of phy_stop_machine
phy_disconnect only then calls phy_detach()
which makes future calls of phy_state_machine perilous.
This all happens in the same thread, so I'm not yet
seeing where the race happens?
The race is as described in David's earlier email, so let's recap:
Thread 1 Thread 2
phy_disconnect()
phy_stop_interrupts()
phy_stop_machine()
phy_state_machine()
-> queue_delayed_work()
phy_detach()
phy_state_machine()
-> netif_carrier_off()
If phy_detach() finishes earlier than the workqueue had a chance
to be
scheduled and process PHY_HALTED again, then we trigger the NULL
pointer
de-reference.
workqueues are not tasklets, the CPU scheduling them gets no
guarantee
they will run on the same CPU.
Something does not add up.
The synchronous call to phy_state_machine() does:
case PHY_HALTED:
if (phydev->link) {
phydev->link = 0;
netif_carrier_off(phydev->attached_dev);
phy_adjust_link(phydev);
do_suspend = true;
}
then sets phydev->link = 0; therefore subsequent calls to
phy_state_machin() will be no-op.
Actually you are right, once phydev->link is set to 0 these would
become
no-ops. Still scratching my head as to what happens for David then...
Also, queue_delayed_work() is only called in polling mode.
David stated that he's using interrupt mode.
Did you see what I wrote?
Still not following, see below.
phy_disconnect() calls phy_stop_interrupts() which puts it into polling
mode. So the polling work gets queued unconditionally.
What part of phy_stop_interrupts() is responsible for changing
phydev->irq to PHY_POLL? free_irq() cannot touch phydev->irq otherwise
subsequent request_irq() calls won't work anymore.
phy_disable_interrupts() only calls back into the PHY driver to
acknowledge and clear interrupts.
If we were using a PHY with PHY_POLL, as Marc said, the first
synchronous call to phy_state_machine() would have acted on PHY_HALTED
and even if we incorrectly keep re-scheduling the state machine from
PHY_HALTED to PHY_HALTED the second time around nothing can happen.
What are we missing here?
OK, I am now as confused as you guys are. I will go back and get an
ftrace log out of the failure.
OK, let's forget about the PHY_HALTED discussion.
Consider instead the case of a Marvell phy with no interrupts connected
on a v4.9.43 kernel, single CPU:
0) | phy_disconnect() {
0) | phy_stop_machine() {
0) | cancel_delayed_work_sync() {
0) + 23.986 us | } /* cancel_delayed_work_sync */
0) | phy_state_machine() {
0) | phy_start_aneg_priv() {
0) | marvell_config_aneg() {
0) ! 240.538 us | } /* marvell_config_aneg */
0) ! 244.971 us | } /* phy_start_aneg_priv */
0) | queue_delayed_work_on() {
0) + 18.016 us | } /* queue_delayed_work_on */
0) ! 268.184 us | } /* phy_state_machine */
0) ! 297.394 us | } /* phy_stop_machine */
0) | phy_detach() {
0) | phy_suspend() {
0) | phy_ethtool_get_wol() {
0) 0.677 us | } /* phy_ethtool_get_wol */
0) | genphy_suspend() {
0) + 71.250 us | } /* genphy_suspend */
0) + 74.197 us | } /* phy_suspend */
0) + 80.302 us | } /* phy_detach */
0) ! 380.072 us | } /* phy_disconnect */
.
.
.
0) | process_one_work() {
0) | find_worker_executing_work() {
0) 0.688 us | } /* find_worker_executing_work */
0) | set_work_pool_and_clear_pending() {
0) 0.734 us | } /* set_work_pool_and_clear_pending */
0) | phy_state_machine() {
0) | genphy_read_status() {
0) ! 205.721 us | } /* genphy_read_status */
0) | netif_carrier_off() {
0) | do_page_fault() {
The do_page_fault() at the end indicates the NULL pointer dereference.
That added call to phy_state_machine() turns the polling back on
unconditionally for a phy that should be disconnected. How is that correct?
David.
