Patch "usb: musb: Fix hardirq-safe hardirq-unsafe lock order error" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

usb: musb: Fix hardirq-safe hardirq-unsafe lock order error

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-musb-fix-hardirq-safe-hardirq-unsafe-lock-order-error.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Tony Lindgren <[email protected]>
Date: Wed, 19 Oct 2016 12:03:39 -0500
Subject: usb: musb: Fix hardirq-safe hardirq-unsafe lock order error

From: Tony Lindgren <[email protected]>

commit d8e5f0eca1e88215e45aca27115ea747e6164da1 upstream.

If we configure musb with 2430 glue as a peripheral, and then rmmod omap2430 module, we'll get the following error:

[ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
...
rmmod/413 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
(&phy->mutex){+.+.+.}, at: [<c04b9fd0>] phy_power_off+0x1c/0xb8

[  204.678710]
               and this task is already holding:
 (&(&musb->lock)->rlock){-.-...}, at: [<bf3a482c>]
 musb_gadget_stop+0x24/0xec [musb_hdrc]

which would create a new lock dependency:
(&(&musb->lock)->rlock){-.-...} -> (&phy->mutex){+.+.+.}
...

This is because some glue layers expect musb_platform_enable/disable to be called with spinlock held, and 2430 glue layer has USB PHY on the I2C bus using a mutex.

We could fix the glue layers to take the spinlock, but we still have a problem of musb_plaform_enable/disable being called in an unbalanced manner. So that would still lead into USB PHY enable/disable related problems for omap2430 glue layer.

While it makes sense to only enable USB PHY when needed from PM point of view, in this case we just can't do it yet without breaking things. So let's just revert phy_enable/disable related changes instead and reconsider this after we have fixed musb_platform_enable/disable to be balanced.

---
 drivers/usb/musb/omap2430.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

@@ -337,6 +337,7 @@ static int omap2430_musb_init(struct mus
 	}
 	musb->isr = omap2430_musb_interrupt;
 	phy_init(musb->phy);
+	phy_power_on(musb->phy);
 
 	l = musb_readl(musb->mregs, OTG_INTERFSEL);
 

@@ -373,8 +374,6 @@ static void omap2430_musb_enable(struct
 	struct musb_hdrc_platform_data *pdata = dev_get_platdata(dev);
 	struct omap_musb_board_data *data = pdata->board_data;
 
-	if (!WARN_ON(!musb->phy))
-		phy_power_on(musb->phy);
 
 	omap2430_set_power(musb, true, glue->cable_connected);
 

@@ -413,9 +412,6 @@ static void omap2430_musb_disable(struct
 	struct device *dev = musb->controller;
 	struct omap2430_glue *glue = dev_get_drvdata(dev->parent);
 
-	if (!WARN_ON(!musb->phy))
-		phy_power_off(musb->phy);
-
 	if (glue->status != MUSB_UNKNOWN)
 		omap_control_usb_set_mode(glue->control_otghs,
 			USB_MODE_DISCONNECT);

@@ -429,6 +425,7 @@ static int omap2430_musb_exit(struct mus
 	struct omap2430_glue *glue = dev_get_drvdata(dev->parent);
 
 	omap2430_low_level_exit(musb);
+	phy_power_off(musb->phy);
 	phy_exit(musb->phy);
 	musb->phy = NULL;
 	cancel_work_sync(&glue->omap_musb_mailbox_work);

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/usb-musb-fix-hardirq-safe-hardirq-unsafe-lock-order-error.patch