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Subject[PATCH 1/2] net: phy: Freeze PHY polling before suspending devices
Date
During system resume, the PHY state machine may be run from the
workqueue while the Ethernet device (and its PHY) are still suspended,
which may lead to a system crash.

E.g. on sh73a0/kzm9g and r8a73a4/ape6evm, the external Ethernet chip is
driven by a PM controlled clock. If the Ethernet registers are accessed
while the clock is not running, the system will crash with an imprecise
external abort.

As this is a race condition with a small time window, it is not so easy
to trigger at will. Using pm_test may increase your chances:

# echo 0 > /sys/module/printk/parameters/console_suspend
# echo platform > /sys/power/pm_test
# echo mem > /sys/power/state

However, since commit 7ad813f208533ceb ("net: phy: Correctly process
PHY_HALTED in phy_stop_machine()"), this is much more likely to happen,
presumably due to the new sync point where phy_state_machine() calls
queue_delayed_work() just before entering system suspend.

To fix this, move PHY polling from the non-freezable to the freezable
power efficient work queue. This is similar to what was done in commit
ea00353f36b64375 ("PCI: Freeze PME scan before suspending devices").

Stacktrace for posterity:

PM: Syncing filesystems ... done.
Freezing user space processes ... (elapsed 0.001 seconds) done.
OOM killer disabled.
Freezing remaining freezable tasks ... (elapsed 0.000 seconds) done.
PM: suspend devices took 0.010 seconds
Disabling non-boot CPUs ...
Enabling non-boot CPUs ...
Unhandled fault: imprecise external abort (0x1406) at 0x000cf6c8
pgd = c0004000
[000cf6c8] *pgd=00000000
Internal error: : 1406 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 57 Comm: kworker/0:2 Not tainted 4.13.0-rc5-kzm9g-04113-g3a897d275111fd6c #903
Hardware name: Generic SH73A0 (Flattened Device Tree)
Workqueue: events_power_efficient phy_state_machine
task: df6b4800 task.stack: df796000
PC is at __smsc911x_reg_read+0x1c/0x60
LR is at smsc911x_mac_read+0x4c/0x118
pc : [<c03c7e88>] lr : [<c03c8b88>] psr: 200d0093
sp : df797e98 ip : 00000000 fp : 00000001
r10: 00000000 r9 : df70e380 r8 : 800d0093
r7 : df631de8 r6 : 00000006 r5 : df631e08 r4 : df631dc0
r3 : e0903000 r2 : 00000000 r1 : e09030a4 r0 : 00000000
Flags: nzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment none
Control: 10c5387d Table: 5ee1404a DAC: 00000051
Process kworker/0:2 (pid: 57, stack limit = 0xdf796210)
Stack: (0xdf797e98 to 0xdf798000)
7e80: df631dc0 00000001
7ea0: 00000001 df631de8 600d0013 c03c8df4 df70e400 00000001 00000001 df70e458
7ec0: df70e000 c03c7104 c03c6170 df70e000 df70e000 dfbc7bc0 df797f30 c03c6138
7ee0: df77d900 c03c617c df77d900 df70e32c dfbc7bc0 c03c4218 df77d900 df70e32c
7f00: dfbc7bc0 df797f30 dfbcb200 00000000 00000000 c013aa0c 00000001 00000000
7f20: c013a994 00000000 00000000 00000000 c1117f70 00000000 00000000 c07420ec
7f40: c0904900 df77d900 dfbc7bc0 dfbc7bc0 df796000 dfbc7bf4 c0904900 df77d918
7f60: 00000008 c013b1e0 df6b4800 df75b500 df77e5c0 00000000 df44dea8 df77d900
7f80: c013af28 df75b538 00000000 c0140584 df77e5c0 c0140460 00000000 00000000
7fa0: 00000000 00000000 00000000 c0106ef0 00000000 00000000 00000000 00000000
7fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
7fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[<c03c7e88>] (__smsc911x_reg_read) from [<c03c8b88>] (smsc911x_mac_read+0x4c/0x118)
[<c03c8b88>] (smsc911x_mac_read) from [<c03c8df4>] (smsc911x_mii_read+0x2c/0xa4)
[<c03c8df4>] (smsc911x_mii_read) from [<c03c7104>] (mdiobus_read+0x58/0x70)
[<c03c7104>] (mdiobus_read) from [<c03c6138>] (genphy_update_link+0x18/0x50)
[<c03c6138>] (genphy_update_link) from [<c03c617c>] (genphy_read_status+0xc/0x1cc)
[<c03c617c>] (genphy_read_status) from [<c03c4218>] (phy_state_machine+0xa8/0x3dc)
[<c03c4218>] (phy_state_machine) from [<c013aa0c>] (process_one_work+0x240/0x3fc)
[<c013aa0c>] (process_one_work) from [<c013b1e0>] (worker_thread+0x2b8/0x3f4)
[<c013b1e0>] (worker_thread) from [<c0140584>] (kthread+0x124/0x144)
[<c0140584>] (kthread) from [<c0106ef0>] (ret_from_fork+0x14/0x24)
Code: e5903000 e0831001 e5910000 f57ff04f (e12fff1e)

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
drivers/net/phy/phy.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index dae13f028c84ee17..2055165ca6349ee5 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -554,7 +554,8 @@ EXPORT_SYMBOL(phy_start_aneg);
*/
void phy_start_machine(struct phy_device *phydev)
{
- queue_delayed_work(system_power_efficient_wq, &phydev->state_queue, HZ);
+ queue_delayed_work(system_freezable_power_efficient_wq,
+ &phydev->state_queue, HZ);
}
EXPORT_SYMBOL_GPL(phy_start_machine);

@@ -574,7 +575,8 @@ void phy_trigger_machine(struct phy_device *phydev, bool sync)
cancel_delayed_work_sync(&phydev->state_queue);
else
cancel_delayed_work(&phydev->state_queue);
- queue_delayed_work(system_power_efficient_wq, &phydev->state_queue, 0);
+ queue_delayed_work(system_freezable_power_efficient_wq,
+ &phydev->state_queue, 0);
}

/**
@@ -1081,8 +1083,8 @@ void phy_state_machine(struct work_struct *work)
* between states from phy_mac_interrupt()
*/
if (phydev->irq == PHY_POLL)
- queue_delayed_work(system_power_efficient_wq, &phydev->state_queue,
- PHY_STATE_TIME * HZ);
+ queue_delayed_work(system_freezable_power_efficient_wq,
+ &phydev->state_queue, PHY_STATE_TIME * HZ);
}

/**
@@ -1099,7 +1101,7 @@ void phy_mac_interrupt(struct phy_device *phydev, int new_link)
phydev->link = new_link;

/* Trigger a state machine change */
- queue_work(system_power_efficient_wq, &phydev->phy_queue);
+ queue_work(system_freezable_power_efficient_wq, &phydev->phy_queue);
}
EXPORT_SYMBOL(phy_mac_interrupt);

--
2.7.4
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