From 541cd3ee00a4fe975b22fac6a3bc846bacef37f7 Mon Sep 17 00:00:00 2001 From: Anton Vorontsov Date: Wed, 30 Dec 2009 08:23:28 +0000 Subject: [PATCH] phylib: Fix deadlock on resume Sometimes kernel hangs on resume with the following trace: ucc_geth e0102000.ucc: resume INFO: task bash:1764 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. bash D 0fecf43c 0 1764 1763 0x00000000 Call Trace: [cf9a7c10] [c0012868] ret_from_except+0x0/0x14 (unreliable) --- Exception: cf9a7ce0 at __switch_to+0x4c/0x6c LR = 0xcf9a7cc0 [cf9a7cd0] [c0008c14] __switch_to+0x4c/0x6c (unreliable) [cf9a7ce0] [c028bcfc] schedule+0x158/0x260 [cf9a7d10] [c028c720] __mutex_lock_slowpath+0x80/0xd8 [cf9a7d40] [c01cf388] phy_stop+0x20/0x70 [cf9a7d50] [c01d514c] ugeth_resume+0x6c/0x13c [...] Here is why. On suspend: - PM core starts suspending devices, ucc_geth_suspend gets called; - ucc_geth calls phy_stop() on suspend. Note that phy_stop() is mostly asynchronous so it doesn't block ucc_geth's suspend routine, it just sets PHY_HALTED state and disables PHY's interrupts; - Suddenly the state machine gets scheduled, it grabs the phydev->lock mutex and tries to process the PHY_HALTED state, so it calls phydev->adjust_link(phydev->attached_dev). In ucc_geth case adjust_link() calls msleep(), which reschedules the code flow back to PM core, which now finishes suspend and so we end up sleeping with phydev->lock mutex held. On resume: - PM core starts resuming devices (notice that nobody rescheduled the state machine yet, so the mutex is still held), the core calls ucc_geth's resume routine; - ucc_geth_resume restarts the PHY with phy_stop()/phy_start() sequence, and the phy_*() calls are trying to grab the phydev->lock mutex. Here comes the deadlock. This patch fixes the issue by stopping the state machine on suspend and starting it again on resume. Signed-off-by: Anton Vorontsov Signed-off-by: David S. Miller --- drivers/net/phy/mdio_bus.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c index bd4e8d72dc08..49252d390903 100644 --- a/drivers/net/phy/mdio_bus.c +++ b/drivers/net/phy/mdio_bus.c @@ -303,8 +303,18 @@ static int mdio_bus_suspend(struct device * dev, pm_message_t state) struct phy_driver *phydrv = to_phy_driver(dev->driver); struct phy_device *phydev = to_phy_device(dev); + /* + * We must stop the state machine manually, otherwise it stops out of + * control, possibly with the phydev->lock held. Upon resume, netdev + * may call phy routines that try to grab the same lock, and that may + * lead to a deadlock. + */ + if (phydev->attached_dev) + phy_stop_machine(phydev); + if (!mdio_bus_phy_may_suspend(phydev)) return 0; + return phydrv->suspend(phydev); } @@ -312,10 +322,20 @@ static int mdio_bus_resume(struct device * dev) { struct phy_driver *phydrv = to_phy_driver(dev->driver); struct phy_device *phydev = to_phy_device(dev); + int ret; if (!mdio_bus_phy_may_suspend(phydev)) - return 0; - return phydrv->resume(phydev); + goto no_resume; + + ret = phydrv->resume(phydev); + if (ret < 0) + return ret; + +no_resume: + if (phydev->attached_dev) + phy_start_machine(phydev, NULL); + + return 0; } struct bus_type mdio_bus_type = { -- 2.34.1