Patch "drm/bridge: adv7511: Fix mutex deadlock when interrupts are disabled" has been added to the 4.4-stable tree

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

drm/bridge: adv7511: Fix mutex deadlock when interrupts are disabled

to the 4.4-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:
drm-bridge-adv7511-fix-mutex-deadlock-when-interrupts-are-disabled.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Archit Taneja <[email protected]>
Date: Wed, 15 Jun 2016 16:20:45 +0530
Subject: drm/bridge: adv7511: Fix mutex deadlock when interrupts are disabled

From: Archit Taneja <[email protected]>

commit f0bfcc22d9822947b0ad3095e8363eab5261864c upstream.

When the adv7511 i2c client doesn't have an interrupt line, we observe a deadlock on caused by trying to lock drm device's mode_config.mutex twice in the same context.

Here is the sequence that causes it:

ioctl DRM_IOCTL_MODE_GETCONNECTOR from userspace
drm_mode_getconnector (acquires mode_config mutex)

    connector->fill_modes()
    drm_helper_probe_single_connector_modes
      connector_funcs->get_modes
	adv7511_encoder_get_modes
	  adv7511_get_edid_block
	    adv7511_irq_process
	      drm_helper_hpd_irq_event (acquires mode_config mutex again)

In adv7511_irq_process, don't call drm_helper_hpd_irq_event when not called from the interrupt handler. It doesn't serve any purpose there anyway.

---
 drivers/gpu/drm/i2c/adv7511.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -429,7 +429,7 @@ static bool adv7511_hpd(struct adv7511 *
 	return false;
 }
 
-static int adv7511_irq_process(struct adv7511 *adv7511)
+static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)
 {
 	unsigned int irq0, irq1;
 	int ret;

@@ -445,7 +445,7 @@ static int adv7511_irq_process(struct ad
 	regmap_write(adv7511->regmap, ADV7511_REG_INT(0), irq0);
 	regmap_write(adv7511->regmap, ADV7511_REG_INT(1), irq1);
 
-	if (irq0 & ADV7511_INT0_HDP && adv7511->encoder)
+	if (process_hpd && irq0 & ADV7511_INT0_HDP && adv7511->encoder)
 		drm_helper_hpd_irq_event(adv7511->encoder->dev);
 
 	if (irq0 & ADV7511_INT0_EDID_READY || irq1 & ADV7511_INT1_DDC_ERROR) {

@@ -463,7 +463,7 @@ static irqreturn_t adv7511_irq_handler(i
 	struct adv7511 *adv7511 = devid;
 	int ret;
 
-	ret = adv7511_irq_process(adv7511);
+	ret = adv7511_irq_process(adv7511, true);
 	return ret < 0 ? IRQ_NONE : IRQ_HANDLED;
 }
 

@@ -480,7 +480,7 @@ static int adv7511_wait_for_edid(struct
 				adv7511->edid_read, msecs_to_jiffies(timeout));
 	} else {
 		for (; timeout > 0; timeout -= 25) {
-			ret = adv7511_irq_process(adv7511);
+			ret = adv7511_irq_process(adv7511, false);
 			if (ret < 0)
 				break;
 

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

queue-4.4/drm-bridge-adv7511-use-work_struct-to-defer-hotplug-handing-to-out-of-irq-context.patch queue-4.4/drm-bridge-adv7511-re-write-the-i2c-address-before-edid-probing.patch queue-4.4/drm-bridge-adv7511-fix-mutex-deadlock-when-interrupts-are-disabled.patch queue-4.4/drm-adv7511-really-enable-interrupts-for-edid-detection.patch queue-4.4/drm-bridge-adv7511-switch-to-using-drm_kms_helper_hotplug_event.patch