linux-kernel - [PATCH 4.4 22/31] drm/bridge: adv7511: Fix mutex deadlock when interrupts are disabled

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Message-Id: <20170912165248.480542824@linuxfoundation.org>
Date:   Tue, 12 Sep 2017 09:56:17 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Archit Taneja <architt@...eaurora.org>,
        Thong Ho <thong.ho.px@....renesas.com>,
        Nhan Nguyen <nhan.nguyen.yb@...esas.com>
Subject: [PATCH 4.4 22/31] drm/bridge: adv7511: Fix mutex deadlock when interrupts are disabled

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Archit Taneja <architt@...eaurora.org>

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.

Signed-off-by: Archit Taneja <architt@...eaurora.org>
Signed-off-by: Thong Ho <thong.ho.px@....renesas.com>
Signed-off-by: Nhan Nguyen <nhan.nguyen.yb@...esas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/i2c/adv7511.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/gpu/drm/i2c/adv7511.c
+++ b/drivers/gpu/drm/i2c/adv7511.c
@@ -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;