[PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Maarten Lankhorst]

mode_valid() and get_modes() called
from drm_helper_probe_single_connector_modes()
may need to look at connector->state because what a valid mode is may
depend on connector properties being set. For example some HDMI modes
might be rejected when a connector property forces the connector
into DVI mode.

Some implementations of detect() already lock all state,
so we have to pass an acquire_ctx to them to prevent a deadlock.

This means changing the function signature of detect() slightly,
and passing the acquire_ctx for locking multiple crtc's.
It might be NULL, in which case expensive operations should be avoided.

intel_dp.c however ignores the force flag, so still lock
connection_mutex there if needed.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
---
 drivers/gpu/drm/drm_probe_helper.c   | 41 ++++++++++++++++++++++++++++++------
 drivers/gpu/drm/i915/intel_crt.c     | 29 +++++++++++++------------
 drivers/gpu/drm/i915/intel_display.c | 25 +++++++++++-----------
 drivers/gpu/drm/i915/intel_dp.c      | 22 ++++++++++++-------
 drivers/gpu/drm/i915/intel_drv.h     |  8 +++----
 drivers/gpu/drm/i915/intel_hotplug.c |  6 +++++-
 drivers/gpu/drm/i915/intel_tv.c      | 24 ++++++++++-----------
 include/drm/drm_connector.h          |  5 +++++
 8 files changed, 101 insertions(+), 59 deletions(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 85005d57bde6..a48cff963871 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -169,11 +169,15 @@ void drm_kms_helper_poll_enable(struct drm_device *dev)
 EXPORT_SYMBOL(drm_kms_helper_poll_enable);
 
 static enum drm_connector_status
-drm_connector_detect(struct drm_connector *connector, bool force)
+drm_connector_detect(struct drm_connector *connector,
+		     struct drm_modeset_acquire_ctx *ctx)
 {
-	return connector->funcs->detect ?
-		connector->funcs->detect(connector, force) :
-		connector_status_connected;
+	if (connector->funcs->detect_ctx)
+		return connector->funcs->detect_ctx(connector, ctx);
+	else if (connector->funcs->detect)
+		return connector->funcs->detect(connector, !!ctx);
+	else
+		return connector_status_connected;
 }
 
 /**
@@ -239,15 +243,27 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
 	struct drm_display_mode *mode;
 	const struct drm_connector_helper_funcs *connector_funcs =
 		connector->helper_private;
-	int count = 0;
+	int count = 0, ret;
 	int mode_flags = 0;
 	bool verbose_prune = true;
 	enum drm_connector_status old_status;
+	struct drm_modeset_acquire_ctx ctx;
 
 	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
 
+	drm_modeset_acquire_init(&ctx, 0);
+
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
 			connector->name);
+
+retry:
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+	if (ret == -EDEADLK) {
+		drm_modeset_backoff(&ctx);
+		goto retry;
+	} else
+		WARN_ON(ret < 0);
+
 	/* set all old modes to the stale state */
 	list_for_each_entry(mode, &connector->modes, head)
 		mode->status = MODE_STALE;
@@ -263,7 +279,15 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
 		if (connector->funcs->force)
 			connector->funcs->force(connector);
 	} else {
-		connector->status = drm_connector_detect(connector, true);
+		ret = drm_connector_detect(connector, &ctx);
+
+		if (ret == -EDEADLK) {
+			drm_modeset_backoff(&ctx);
+			goto retry;
+		} else if (WARN(ret < 0, "Invalid return value %i for connector detection\n", ret))
+			ret = connector_status_unknown;
+
+		connector->status = ret;
 	}
 
 	/*
@@ -355,6 +379,9 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
 prune:
 	drm_mode_prune_invalid(dev, &connector->modes, verbose_prune);
 
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+
 	if (list_empty(&connector->modes))
 		return 0;
 
@@ -440,7 +467,7 @@ static void output_poll_execute(struct work_struct *work)
 
 		repoll = true;
 
-		connector->status = drm_connector_detect(connector, false);
+		connector->status = drm_connector_detect(connector, NULL);
 		if (old_status != connector->status) {
 			const char *old, *new;
 
diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 8c82607294c6..1186c3f5fea0 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -669,19 +669,19 @@ static const struct dmi_system_id intel_spurious_crt_detect[] = {
 	{ }
 };
 
-static enum drm_connector_status
-intel_crt_detect(struct drm_connector *connector, bool force)
+static int
+intel_crt_detect(struct drm_connector *connector,
+		 struct drm_modeset_acquire_ctx *ctx)
 {
 	struct drm_i915_private *dev_priv = to_i915(connector->dev);
 	struct intel_crt *crt = intel_attached_crt(connector);
 	struct intel_encoder *intel_encoder = &crt->base;
-	enum drm_connector_status status;
+	int status, ret;
 	struct intel_load_detect_pipe tmp;
-	struct drm_modeset_acquire_ctx ctx;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
 		      connector->base.id, connector->name,
-		      force);
+		      !!ctx);
 
 	/* Skip machines without VGA that falsely report hotplug events */
 	if (dmi_check_system(intel_spurious_crt_detect))
@@ -716,15 +716,19 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 		goto out;
 	}
 
-	if (!force) {
+	if (!ctx) {
 		status = connector->status;
 		goto out;
 	}
 
-	drm_modeset_acquire_init(&ctx, 0);
-
 	/* for pre-945g platforms use load detect */
-	if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
+	ret = intel_get_load_detect_pipe(connector, NULL, &tmp, ctx);
+	if (ret < 0) {
+		status = ret;
+		goto out;
+	}
+
+	if (ret > 0) {
 		if (intel_crt_detect_ddc(connector))
 			status = connector_status_connected;
 		else if (INTEL_GEN(dev_priv) < 4)
@@ -734,13 +738,10 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 			status = connector_status_disconnected;
 		else
 			status = connector_status_unknown;
-		intel_release_load_detect_pipe(connector, &tmp, &ctx);
+		intel_release_load_detect_pipe(connector, &tmp, ctx);
 	} else
 		status = connector_status_unknown;
 
-	drm_modeset_drop_locks(&ctx);
-	drm_modeset_acquire_fini(&ctx);
-
 out:
 	intel_display_power_put(dev_priv, intel_encoder->power_domain);
 	return status;
@@ -811,7 +812,7 @@ void intel_crt_reset(struct drm_encoder *encoder)
 
 static const struct drm_connector_funcs intel_crt_connector_funcs = {
 	.dpms = drm_atomic_helper_connector_dpms,
-	.detect = intel_crt_detect,
+	.detect_ctx = intel_crt_detect,
 	.fill_modes = drm_helper_probe_single_connector_modes,
 	.late_register = intel_connector_register,
 	.early_unregister = intel_connector_unregister,
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a79063fac951..baa8d836c8e7 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9503,10 +9503,10 @@ static int intel_modeset_setup_plane_state(struct drm_atomic_state *state,
 	return 0;
 }
 
-bool intel_get_load_detect_pipe(struct drm_connector *connector,
-				struct drm_display_mode *mode,
-				struct intel_load_detect_pipe *old,
-				struct drm_modeset_acquire_ctx *ctx)
+int intel_get_load_detect_pipe(struct drm_connector *connector,
+			       struct drm_display_mode *mode,
+			       struct intel_load_detect_pipe *old,
+			       struct drm_modeset_acquire_ctx *ctx)
 {
 	struct intel_crtc *intel_crtc;
 	struct intel_encoder *intel_encoder =
@@ -9529,10 +9529,7 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
 
 	old->restore_state = NULL;
 
-retry:
-	ret = drm_modeset_lock(&config->connection_mutex, ctx);
-	if (ret)
-		goto fail;
+	WARN_ON(!drm_modeset_is_locked(&config->connection_mutex));
 
 	/*
 	 * Algorithm gets a little messy:
@@ -9682,10 +9679,8 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
 		restore_state = NULL;
 	}
 
-	if (ret == -EDEADLK) {
-		drm_modeset_backoff(ctx);
-		goto retry;
-	}
+	if (ret == -EDEADLK)
+		return ret;
 
 	return false;
 }
@@ -15112,6 +15107,7 @@ static void intel_enable_pipe_a(struct drm_device *dev)
 	struct drm_connector *crt = NULL;
 	struct intel_load_detect_pipe load_detect_temp;
 	struct drm_modeset_acquire_ctx *ctx = dev->mode_config.acquire_ctx;
+	int ret;
 
 	/* We can't just switch on the pipe A, we need to set things up with a
 	 * proper mode and output configuration. As a gross hack, enable pipe A
@@ -15128,7 +15124,10 @@ static void intel_enable_pipe_a(struct drm_device *dev)
 	if (!crt)
 		return;
 
-	if (intel_get_load_detect_pipe(crt, NULL, &load_detect_temp, ctx))
+	ret = intel_get_load_detect_pipe(crt, NULL, &load_detect_temp, ctx);
+	WARN(ret < 0, "All modeset mutexes are locked, but intel_get_load_detect_pipe failed\n");
+
+	if (ret > 0)
 		intel_release_load_detect_pipe(crt, &load_detect_temp, ctx);
 }
 
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index fd96a6cf7326..10b3727b7381 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4567,7 +4567,8 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
 }
 
 static enum drm_connector_status
-intel_dp_long_pulse(struct intel_connector *intel_connector)
+intel_dp_long_pulse(struct intel_connector *intel_connector,
+		    struct drm_modeset_acquire_ctx *ctx)
 {
 	struct drm_connector *connector = &intel_connector->base;
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
@@ -4640,9 +4641,13 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 		 * check links status, there has been known issues of
 		 * link loss triggerring long pulse!!!!
 		 */
-		drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
+		if (!ctx)
+			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
+
 		intel_dp_check_link_status(intel_dp);
-		drm_modeset_unlock(&dev->mode_config.connection_mutex);
+
+		if (!ctx)
+			drm_modeset_unlock(&dev->mode_config.connection_mutex);
 		goto out;
 	}
 
@@ -4682,18 +4687,19 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 	return status;
 }
 
-static enum drm_connector_status
-intel_dp_detect(struct drm_connector *connector, bool force)
+static int
+intel_dp_detect(struct drm_connector *connector,
+		struct drm_modeset_acquire_ctx *ctx)
 {
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	enum drm_connector_status status = connector->status;
+	int status = connector->status;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
 		      connector->base.id, connector->name);
 
 	/* If full detect is not performed yet, do a full detect */
 	if (!intel_dp->detect_done)
-		status = intel_dp_long_pulse(intel_dp->attached_connector);
+		status = intel_dp_long_pulse(intel_dp->attached_connector, ctx);
 
 	intel_dp->detect_done = false;
 
@@ -5014,7 +5020,7 @@ void intel_dp_encoder_reset(struct drm_encoder *encoder)
 
 static const struct drm_connector_funcs intel_dp_connector_funcs = {
 	.dpms = drm_atomic_helper_connector_dpms,
-	.detect = intel_dp_detect,
+	.detect_ctx = intel_dp_detect,
 	.force = intel_dp_force,
 	.fill_modes = drm_helper_probe_single_connector_modes,
 	.set_property = intel_dp_set_property,
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index e24641b559e2..6ea8b9cd68c5 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1362,10 +1362,10 @@ int ironlake_get_lanes_required(int target_clock, int link_bw, int bpp);
 void vlv_wait_port_ready(struct drm_i915_private *dev_priv,
 			 struct intel_digital_port *dport,
 			 unsigned int expected_mask);
-bool intel_get_load_detect_pipe(struct drm_connector *connector,
-				struct drm_display_mode *mode,
-				struct intel_load_detect_pipe *old,
-				struct drm_modeset_acquire_ctx *ctx);
+int intel_get_load_detect_pipe(struct drm_connector *connector,
+			       struct drm_display_mode *mode,
+			       struct intel_load_detect_pipe *old,
+			       struct drm_modeset_acquire_ctx *ctx);
 void intel_release_load_detect_pipe(struct drm_connector *connector,
 				    struct intel_load_detect_pipe *old,
 				    struct drm_modeset_acquire_ctx *ctx);
diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
index 7d210097eefa..d2d2af7ef305 100644
--- a/drivers/gpu/drm/i915/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/intel_hotplug.c
@@ -243,7 +243,11 @@ static bool intel_hpd_irq_event(struct drm_device *dev,
 	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
 	old_status = connector->status;
 
-	connector->status = connector->funcs->detect(connector, false);
+	if (connector->funcs->detect_ctx)
+		connector->status = connector->funcs->detect_ctx(connector, NULL);
+	else
+		connector->status = connector->funcs->detect(connector, false);
+
 	if (old_status == connector->status)
 		return false;
 
diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index 6ed1a3ce47b7..d2c0120048b2 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1315,8 +1315,9 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
  * Currently this always returns CONNECTOR_STATUS_UNKNOWN, as we need to be sure
  * we have a pipe programmed in order to probe the TV.
  */
-static enum drm_connector_status
-intel_tv_detect(struct drm_connector *connector, bool force)
+static int
+intel_tv_detect(struct drm_connector *connector,
+		struct drm_modeset_acquire_ctx *ctx)
 {
 	struct drm_display_mode mode;
 	struct intel_tv *intel_tv = intel_attached_tv(connector);
@@ -1325,27 +1326,26 @@ intel_tv_detect(struct drm_connector *connector, bool force)
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
 		      connector->base.id, connector->name,
-		      force);
+		      !!ctx);
 
 	mode = reported_modes[0];
 
-	if (force) {
+	if (ctx) {
 		struct intel_load_detect_pipe tmp;
-		struct drm_modeset_acquire_ctx ctx;
+		int ret;
 
-		drm_modeset_acquire_init(&ctx, 0);
+		ret = intel_get_load_detect_pipe(connector, &mode, &tmp, ctx);
+		if (ret < 0)
+			return ret;
 
-		if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
+		if (ret > 0) {
 			type = intel_tv_detect_type(intel_tv, connector);
-			intel_release_load_detect_pipe(connector, &tmp, &ctx);
+			intel_release_load_detect_pipe(connector, &tmp, ctx);
 			status = type < 0 ?
 				connector_status_disconnected :
 				connector_status_connected;
 		} else
 			status = connector_status_unknown;
-
-		drm_modeset_drop_locks(&ctx);
-		drm_modeset_acquire_fini(&ctx);
 	} else
 		return connector->status;
 
@@ -1516,7 +1516,7 @@ intel_tv_set_property(struct drm_connector *connector, struct drm_property *prop
 
 static const struct drm_connector_funcs intel_tv_connector_funcs = {
 	.dpms = drm_atomic_helper_connector_dpms,
-	.detect = intel_tv_detect,
+	.detect_ctx = intel_tv_detect,
 	.late_register = intel_connector_register,
 	.early_unregister = intel_connector_unregister,
 	.destroy = intel_tv_destroy,
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 941f57f311aa..834d1ba709ea 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -32,6 +32,7 @@
 struct drm_device;
 
 struct drm_connector_helper_funcs;
+struct drm_modeset_acquire_ctx;
 struct drm_device;
 struct drm_crtc;
 struct drm_encoder;
@@ -385,6 +386,10 @@ struct drm_connector_funcs {
 	enum drm_connector_status (*detect)(struct drm_connector *connector,
 					    bool force);
 
+	/* ctx = NULL <> detect(force = false), but may also return -EDEADLK. */
+	int (*detect_ctx)(struct drm_connector *connector,
+			  struct drm_modeset_acquire_ctx *ctx);
+
 	/**
 	 * @force:
 	 *
-- 
2.7.4

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✓ Fi.CI.BAT: success for drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Patchwork]

== Series Details ==

Series: drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.
URL   : https://patchwork.freedesktop.org/series/22073/
State : success

== Summary ==

Series 22073v1 drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.
https://patchwork.freedesktop.org/api/1.0/series/22073/revisions/1/mbox/

Test gem_exec_suspend:
        Subgroup basic-s4-devices:
                dmesg-warn -> PASS       (fi-kbl-7560u) fdo#100428
                dmesg-warn -> PASS       (fi-snb-2600)

fdo#100428 https://bugs.freedesktop.org/show_bug.cgi?id=100428

fi-bdw-5557u     total:278  pass:267  dwarn:0   dfail:0   fail:0   skip:11  time: 466s
fi-bdw-gvtdvm    total:278  pass:256  dwarn:8   dfail:0   fail:0   skip:14  time: 453s
fi-bsw-n3050     total:278  pass:239  dwarn:0   dfail:0   fail:0   skip:39  time: 583s
fi-bxt-j4205     total:278  pass:259  dwarn:0   dfail:0   fail:0   skip:19  time: 538s
fi-bxt-t5700     total:278  pass:258  dwarn:0   dfail:0   fail:0   skip:20  time: 582s
fi-byt-j1900     total:278  pass:251  dwarn:0   dfail:0   fail:0   skip:27  time: 502s
fi-byt-n2820     total:278  pass:247  dwarn:0   dfail:0   fail:0   skip:31  time: 510s
fi-hsw-4770      total:278  pass:262  dwarn:0   dfail:0   fail:0   skip:16  time: 436s
fi-hsw-4770r     total:278  pass:262  dwarn:0   dfail:0   fail:0   skip:16  time: 432s
fi-ilk-650       total:278  pass:228  dwarn:0   dfail:0   fail:0   skip:50  time: 435s
fi-ivb-3520m     total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time: 513s
fi-ivb-3770      total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time: 495s
fi-kbl-7500u     total:278  pass:260  dwarn:0   dfail:0   fail:0   skip:18  time: 481s
fi-kbl-7560u     total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time: 594s
fi-skl-6260u     total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time: 479s
fi-skl-6700hq    total:278  pass:261  dwarn:0   dfail:0   fail:0   skip:17  time: 597s
fi-skl-6700k     total:278  pass:256  dwarn:4   dfail:0   fail:0   skip:18  time: 494s
fi-skl-6770hq    total:278  pass:268  dwarn:0   dfail:0   fail:0   skip:10  time: 523s
fi-skl-gvtdvm    total:278  pass:265  dwarn:0   dfail:0   fail:0   skip:13  time: 470s
fi-snb-2520m     total:278  pass:250  dwarn:0   dfail:0   fail:0   skip:28  time: 546s
fi-snb-2600      total:278  pass:249  dwarn:0   dfail:0   fail:0   skip:29  time: 420s

1610e07cbf696204259f584fcc74fde1c16a4d29 drm-tip: 2017y-03m-29d-10h-12m-03s UTC integration manifest
7205f15 drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

== Logs ==

For more details see: https://intel-gfx-ci.01.org/CI/Patchwork_4337/
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Re: [PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Daniel Vetter]

On Wed, Mar 29, 2017 at 12:16:50PM +0200, Maarten Lankhorst wrote:
> mode_valid() and get_modes() called
> from drm_helper_probe_single_connector_modes()
> may need to look at connector->state because what a valid mode is may
> depend on connector properties being set. For example some HDMI modes
> might be rejected when a connector property forces the connector
> into DVI mode.
> 
> Some implementations of detect() already lock all state,
> so we have to pass an acquire_ctx to them to prevent a deadlock.
> 
> This means changing the function signature of detect() slightly,
> and passing the acquire_ctx for locking multiple crtc's.
> It might be NULL, in which case expensive operations should be avoided.
> 
> intel_dp.c however ignores the force flag, so still lock
> connection_mutex there if needed.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>

Hm only noticed this now, but mixing up force with the acquire_ctx sounds
like very bad interface design. Yes, the only user of the new hook works
like that, but that's really accidental I think. I think just having the
ctx everywhere (for atomic drivers at least) would be a lot safer. This is
extremely surprising (and undocumented suprise at that).

> ---
>  drivers/gpu/drm/drm_probe_helper.c   | 41 ++++++++++++++++++++++++++++++------
>  drivers/gpu/drm/i915/intel_crt.c     | 29 +++++++++++++------------
>  drivers/gpu/drm/i915/intel_display.c | 25 +++++++++++-----------
>  drivers/gpu/drm/i915/intel_dp.c      | 22 ++++++++++++-------
>  drivers/gpu/drm/i915/intel_drv.h     |  8 +++----
>  drivers/gpu/drm/i915/intel_hotplug.c |  6 +++++-
>  drivers/gpu/drm/i915/intel_tv.c      | 24 ++++++++++-----------
>  include/drm/drm_connector.h          |  5 +++++
>  8 files changed, 101 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 85005d57bde6..a48cff963871 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -169,11 +169,15 @@ void drm_kms_helper_poll_enable(struct drm_device *dev)
>  EXPORT_SYMBOL(drm_kms_helper_poll_enable);
>  
>  static enum drm_connector_status
> -drm_connector_detect(struct drm_connector *connector, bool force)
> +drm_connector_detect(struct drm_connector *connector,
> +		     struct drm_modeset_acquire_ctx *ctx)
>  {
> -	return connector->funcs->detect ?
> -		connector->funcs->detect(connector, force) :
> -		connector_status_connected;
> +	if (connector->funcs->detect_ctx)
> +		return connector->funcs->detect_ctx(connector, ctx);
> +	else if (connector->funcs->detect)
> +		return connector->funcs->detect(connector, !!ctx);
> +	else
> +		return connector_status_connected;
>  }
>  
>  /**
> @@ -239,15 +243,27 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  	struct drm_display_mode *mode;
>  	const struct drm_connector_helper_funcs *connector_funcs =
>  		connector->helper_private;
> -	int count = 0;
> +	int count = 0, ret;
>  	int mode_flags = 0;
>  	bool verbose_prune = true;
>  	enum drm_connector_status old_status;
> +	struct drm_modeset_acquire_ctx ctx;
>  
>  	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
>  
> +	drm_modeset_acquire_init(&ctx, 0);
> +
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
>  			connector->name);
> +
> +retry:
> +	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
> +	if (ret == -EDEADLK) {
> +		drm_modeset_backoff(&ctx);
> +		goto retry;
> +	} else
> +		WARN_ON(ret < 0);
> +
>  	/* set all old modes to the stale state */
>  	list_for_each_entry(mode, &connector->modes, head)
>  		mode->status = MODE_STALE;
> @@ -263,7 +279,15 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  		if (connector->funcs->force)
>  			connector->funcs->force(connector);
>  	} else {
> -		connector->status = drm_connector_detect(connector, true);
> +		ret = drm_connector_detect(connector, &ctx);
> +
> +		if (ret == -EDEADLK) {
> +			drm_modeset_backoff(&ctx);
> +			goto retry;
> +		} else if (WARN(ret < 0, "Invalid return value %i for connector detection\n", ret))
> +			ret = connector_status_unknown;
> +
> +		connector->status = ret;
>  	}
>  
>  	/*
> @@ -355,6 +379,9 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  prune:
>  	drm_mode_prune_invalid(dev, &connector->modes, verbose_prune);
>  
> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +
>  	if (list_empty(&connector->modes))
>  		return 0;
>  
> @@ -440,7 +467,7 @@ static void output_poll_execute(struct work_struct *work)
>  
>  		repoll = true;
>  
> -		connector->status = drm_connector_detect(connector, false);
> +		connector->status = drm_connector_detect(connector, NULL);
>  		if (old_status != connector->status) {
>  			const char *old, *new;
>  
> diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
> index 8c82607294c6..1186c3f5fea0 100644
> --- a/drivers/gpu/drm/i915/intel_crt.c
> +++ b/drivers/gpu/drm/i915/intel_crt.c
> @@ -669,19 +669,19 @@ static const struct dmi_system_id intel_spurious_crt_detect[] = {
>  	{ }
>  };
>  
> -static enum drm_connector_status
> -intel_crt_detect(struct drm_connector *connector, bool force)
> +static int
> +intel_crt_detect(struct drm_connector *connector,
> +		 struct drm_modeset_acquire_ctx *ctx)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(connector->dev);
>  	struct intel_crt *crt = intel_attached_crt(connector);
>  	struct intel_encoder *intel_encoder = &crt->base;
> -	enum drm_connector_status status;
> +	int status, ret;
>  	struct intel_load_detect_pipe tmp;
> -	struct drm_modeset_acquire_ctx ctx;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
>  		      connector->base.id, connector->name,
> -		      force);
> +		      !!ctx);
>  
>  	/* Skip machines without VGA that falsely report hotplug events */
>  	if (dmi_check_system(intel_spurious_crt_detect))
> @@ -716,15 +716,19 @@ intel_crt_detect(struct drm_connector *connector, bool force)
>  		goto out;
>  	}
>  
> -	if (!force) {
> +	if (!ctx) {
>  		status = connector->status;
>  		goto out;
>  	}
>  
> -	drm_modeset_acquire_init(&ctx, 0);
> -
>  	/* for pre-945g platforms use load detect */
> -	if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
> +	ret = intel_get_load_detect_pipe(connector, NULL, &tmp, ctx);
> +	if (ret < 0) {
> +		status = ret;
> +		goto out;
> +	}
> +
> +	if (ret > 0) {
>  		if (intel_crt_detect_ddc(connector))
>  			status = connector_status_connected;
>  		else if (INTEL_GEN(dev_priv) < 4)
> @@ -734,13 +738,10 @@ intel_crt_detect(struct drm_connector *connector, bool force)
>  			status = connector_status_disconnected;
>  		else
>  			status = connector_status_unknown;
> -		intel_release_load_detect_pipe(connector, &tmp, &ctx);
> +		intel_release_load_detect_pipe(connector, &tmp, ctx);
>  	} else
>  		status = connector_status_unknown;
>  
> -	drm_modeset_drop_locks(&ctx);
> -	drm_modeset_acquire_fini(&ctx);
> -
>  out:
>  	intel_display_power_put(dev_priv, intel_encoder->power_domain);
>  	return status;
> @@ -811,7 +812,7 @@ void intel_crt_reset(struct drm_encoder *encoder)
>  
>  static const struct drm_connector_funcs intel_crt_connector_funcs = {
>  	.dpms = drm_atomic_helper_connector_dpms,
> -	.detect = intel_crt_detect,
> +	.detect_ctx = intel_crt_detect,
>  	.fill_modes = drm_helper_probe_single_connector_modes,
>  	.late_register = intel_connector_register,
>  	.early_unregister = intel_connector_unregister,
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index a79063fac951..baa8d836c8e7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9503,10 +9503,10 @@ static int intel_modeset_setup_plane_state(struct drm_atomic_state *state,
>  	return 0;
>  }
>  
> -bool intel_get_load_detect_pipe(struct drm_connector *connector,
> -				struct drm_display_mode *mode,
> -				struct intel_load_detect_pipe *old,
> -				struct drm_modeset_acquire_ctx *ctx)
> +int intel_get_load_detect_pipe(struct drm_connector *connector,
> +			       struct drm_display_mode *mode,
> +			       struct intel_load_detect_pipe *old,
> +			       struct drm_modeset_acquire_ctx *ctx)
>  {
>  	struct intel_crtc *intel_crtc;
>  	struct intel_encoder *intel_encoder =
> @@ -9529,10 +9529,7 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
>  
>  	old->restore_state = NULL;
>  
> -retry:
> -	ret = drm_modeset_lock(&config->connection_mutex, ctx);
> -	if (ret)
> -		goto fail;
> +	WARN_ON(!drm_modeset_is_locked(&config->connection_mutex));
>  
>  	/*
>  	 * Algorithm gets a little messy:
> @@ -9682,10 +9679,8 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
>  		restore_state = NULL;
>  	}
>  
> -	if (ret == -EDEADLK) {
> -		drm_modeset_backoff(ctx);
> -		goto retry;
> -	}
> +	if (ret == -EDEADLK)
> +		return ret;
>  
>  	return false;
>  }
> @@ -15112,6 +15107,7 @@ static void intel_enable_pipe_a(struct drm_device *dev)
>  	struct drm_connector *crt = NULL;
>  	struct intel_load_detect_pipe load_detect_temp;
>  	struct drm_modeset_acquire_ctx *ctx = dev->mode_config.acquire_ctx;
> +	int ret;
>  
>  	/* We can't just switch on the pipe A, we need to set things up with a
>  	 * proper mode and output configuration. As a gross hack, enable pipe A
> @@ -15128,7 +15124,10 @@ static void intel_enable_pipe_a(struct drm_device *dev)
>  	if (!crt)
>  		return;
>  
> -	if (intel_get_load_detect_pipe(crt, NULL, &load_detect_temp, ctx))
> +	ret = intel_get_load_detect_pipe(crt, NULL, &load_detect_temp, ctx);
> +	WARN(ret < 0, "All modeset mutexes are locked, but intel_get_load_detect_pipe failed\n");
> +
> +	if (ret > 0)
>  		intel_release_load_detect_pipe(crt, &load_detect_temp, ctx);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index fd96a6cf7326..10b3727b7381 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4567,7 +4567,8 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
>  }
>  
>  static enum drm_connector_status
> -intel_dp_long_pulse(struct intel_connector *intel_connector)
> +intel_dp_long_pulse(struct intel_connector *intel_connector,
> +		    struct drm_modeset_acquire_ctx *ctx)
>  {
>  	struct drm_connector *connector = &intel_connector->base;
>  	struct intel_dp *intel_dp = intel_attached_dp(connector);
> @@ -4640,9 +4641,13 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
>  		 * check links status, there has been known issues of
>  		 * link loss triggerring long pulse!!!!
>  		 */
> -		drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> +		if (!ctx)
> +			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> +
>  		intel_dp_check_link_status(intel_dp);
> -		drm_modeset_unlock(&dev->mode_config.connection_mutex);
> +
> +		if (!ctx)
> +			drm_modeset_unlock(&dev->mode_config.connection_mutex);
>  		goto out;
>  	}
>  
> @@ -4682,18 +4687,19 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
>  	return status;
>  }
>  
> -static enum drm_connector_status
> -intel_dp_detect(struct drm_connector *connector, bool force)
> +static int
> +intel_dp_detect(struct drm_connector *connector,
> +		struct drm_modeset_acquire_ctx *ctx)
>  {
>  	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	enum drm_connector_status status = connector->status;
> +	int status = connector->status;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
>  		      connector->base.id, connector->name);
>  
>  	/* If full detect is not performed yet, do a full detect */
>  	if (!intel_dp->detect_done)
> -		status = intel_dp_long_pulse(intel_dp->attached_connector);
> +		status = intel_dp_long_pulse(intel_dp->attached_connector, ctx);
>  
>  	intel_dp->detect_done = false;
>  
> @@ -5014,7 +5020,7 @@ void intel_dp_encoder_reset(struct drm_encoder *encoder)
>  
>  static const struct drm_connector_funcs intel_dp_connector_funcs = {
>  	.dpms = drm_atomic_helper_connector_dpms,
> -	.detect = intel_dp_detect,
> +	.detect_ctx = intel_dp_detect,
>  	.force = intel_dp_force,
>  	.fill_modes = drm_helper_probe_single_connector_modes,
>  	.set_property = intel_dp_set_property,
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index e24641b559e2..6ea8b9cd68c5 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1362,10 +1362,10 @@ int ironlake_get_lanes_required(int target_clock, int link_bw, int bpp);
>  void vlv_wait_port_ready(struct drm_i915_private *dev_priv,
>  			 struct intel_digital_port *dport,
>  			 unsigned int expected_mask);
> -bool intel_get_load_detect_pipe(struct drm_connector *connector,
> -				struct drm_display_mode *mode,
> -				struct intel_load_detect_pipe *old,
> -				struct drm_modeset_acquire_ctx *ctx);
> +int intel_get_load_detect_pipe(struct drm_connector *connector,
> +			       struct drm_display_mode *mode,
> +			       struct intel_load_detect_pipe *old,
> +			       struct drm_modeset_acquire_ctx *ctx);
>  void intel_release_load_detect_pipe(struct drm_connector *connector,
>  				    struct intel_load_detect_pipe *old,
>  				    struct drm_modeset_acquire_ctx *ctx);
> diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> index 7d210097eefa..d2d2af7ef305 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -243,7 +243,11 @@ static bool intel_hpd_irq_event(struct drm_device *dev,
>  	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
>  	old_status = connector->status;
>  
> -	connector->status = connector->funcs->detect(connector, false);
> +	if (connector->funcs->detect_ctx)
> +		connector->status = connector->funcs->detect_ctx(connector, NULL);
> +	else
> +		connector->status = connector->funcs->detect(connector, false);
> +
>  	if (old_status == connector->status)
>  		return false;
>  
> diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
> index 6ed1a3ce47b7..d2c0120048b2 100644
> --- a/drivers/gpu/drm/i915/intel_tv.c
> +++ b/drivers/gpu/drm/i915/intel_tv.c
> @@ -1315,8 +1315,9 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
>   * Currently this always returns CONNECTOR_STATUS_UNKNOWN, as we need to be sure
>   * we have a pipe programmed in order to probe the TV.
>   */
> -static enum drm_connector_status
> -intel_tv_detect(struct drm_connector *connector, bool force)
> +static int
> +intel_tv_detect(struct drm_connector *connector,
> +		struct drm_modeset_acquire_ctx *ctx)
>  {
>  	struct drm_display_mode mode;
>  	struct intel_tv *intel_tv = intel_attached_tv(connector);
> @@ -1325,27 +1326,26 @@ intel_tv_detect(struct drm_connector *connector, bool force)
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
>  		      connector->base.id, connector->name,
> -		      force);
> +		      !!ctx);
>  
>  	mode = reported_modes[0];
>  
> -	if (force) {
> +	if (ctx) {
>  		struct intel_load_detect_pipe tmp;
> -		struct drm_modeset_acquire_ctx ctx;
> +		int ret;
>  
> -		drm_modeset_acquire_init(&ctx, 0);
> +		ret = intel_get_load_detect_pipe(connector, &mode, &tmp, ctx);
> +		if (ret < 0)
> +			return ret;
>  
> -		if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
> +		if (ret > 0) {
>  			type = intel_tv_detect_type(intel_tv, connector);
> -			intel_release_load_detect_pipe(connector, &tmp, &ctx);
> +			intel_release_load_detect_pipe(connector, &tmp, ctx);
>  			status = type < 0 ?
>  				connector_status_disconnected :
>  				connector_status_connected;
>  		} else
>  			status = connector_status_unknown;
> -
> -		drm_modeset_drop_locks(&ctx);
> -		drm_modeset_acquire_fini(&ctx);
>  	} else
>  		return connector->status;
>  
> @@ -1516,7 +1516,7 @@ intel_tv_set_property(struct drm_connector *connector, struct drm_property *prop
>  
>  static const struct drm_connector_funcs intel_tv_connector_funcs = {
>  	.dpms = drm_atomic_helper_connector_dpms,
> -	.detect = intel_tv_detect,
> +	.detect_ctx = intel_tv_detect,
>  	.late_register = intel_connector_register,
>  	.early_unregister = intel_connector_unregister,
>  	.destroy = intel_tv_destroy,
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 941f57f311aa..834d1ba709ea 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -32,6 +32,7 @@
>  struct drm_device;
>  
>  struct drm_connector_helper_funcs;
> +struct drm_modeset_acquire_ctx;
>  struct drm_device;
>  struct drm_crtc;
>  struct drm_encoder;
> @@ -385,6 +386,10 @@ struct drm_connector_funcs {
>  	enum drm_connector_status (*detect)(struct drm_connector *connector,
>  					    bool force);
>  
> +	/* ctx = NULL <> detect(force = false), but may also return -EDEADLK. */

At least copy-paste the kernel-doc for the existing hook. And run make
hmtldocs to check it ...

When doing that you'll also notice that there's a FIXME telling you the
hook should probably be in drm_connector_helper_funcs.

Thanks, Daniel

> +	int (*detect_ctx)(struct drm_connector *connector,
> +			  struct drm_modeset_acquire_ctx *ctx);
> +
>  	/**
>  	 * @force:
>  	 *
> -- 
> 2.7.4
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [Intel-gfx] [PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Boris Brezillon]

On Wed, 29 Mar 2017 15:26:45 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:

> On Wed, Mar 29, 2017 at 12:16:50PM +0200, Maarten Lankhorst wrote:
> > mode_valid() and get_modes() called
> > from drm_helper_probe_single_connector_modes()
> > may need to look at connector->state because what a valid mode is may
> > depend on connector properties being set. For example some HDMI modes
> > might be rejected when a connector property forces the connector
> > into DVI mode.
> > 
> > Some implementations of detect() already lock all state,
> > so we have to pass an acquire_ctx to them to prevent a deadlock.
> > 
> > This means changing the function signature of detect() slightly,
> > and passing the acquire_ctx for locking multiple crtc's.
> > It might be NULL, in which case expensive operations should be avoided.
> > 
> > intel_dp.c however ignores the force flag, so still lock
> > connection_mutex there if needed.
> > 
> > Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
> > Cc: Manasi Navare <manasi.d.navare@intel.com>  
> 
> Hm only noticed this now, but mixing up force with the acquire_ctx sounds
> like very bad interface design. Yes, the only user of the new hook works
> like that, but that's really accidental I think. I think just having the
> ctx everywhere (for atomic drivers at least) would be a lot safer. This is
> extremely surprising (and undocumented suprise at that).

Yes, I was about to say the same thing: the interface is not very
clear, and I don't understand why ctx = NULL implies force = false.
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Re: [Intel-gfx] [PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Maarten Lankhorst]

Op 29-03-17 om 15:31 schreef Boris Brezillon:
> On Wed, 29 Mar 2017 15:26:45 +0200
> Daniel Vetter <daniel@ffwll.ch> wrote:
>
>> On Wed, Mar 29, 2017 at 12:16:50PM +0200, Maarten Lankhorst wrote:
>>> mode_valid() and get_modes() called
>>> from drm_helper_probe_single_connector_modes()
>>> may need to look at connector->state because what a valid mode is may
>>> depend on connector properties being set. For example some HDMI modes
>>> might be rejected when a connector property forces the connector
>>> into DVI mode.
>>>
>>> Some implementations of detect() already lock all state,
>>> so we have to pass an acquire_ctx to them to prevent a deadlock.
>>>
>>> This means changing the function signature of detect() slightly,
>>> and passing the acquire_ctx for locking multiple crtc's.
>>> It might be NULL, in which case expensive operations should be avoided.
>>>
>>> intel_dp.c however ignores the force flag, so still lock
>>> connection_mutex there if needed.
>>>
>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>> Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
>>> Cc: Manasi Navare <manasi.d.navare@intel.com>  
>> Hm only noticed this now, but mixing up force with the acquire_ctx sounds
>> like very bad interface design. Yes, the only user of the new hook works
>> like that, but that's really accidental I think. I think just having the
>> ctx everywhere (for atomic drivers at least) would be a lot safer. This is
>> extremely surprising (and undocumented suprise at that).
> Yes, I was about to say the same thing: the interface is not very
> clear, and I don't understand why ctx = NULL implies force = false.

They're the same thing I fear. I could perhaps call it force_ctx instead,
but non-zero ctx implies force, and other way around. Though I guess we could
relax it, and have force = true imply ctx, but not the other way around.

Would that be ok?

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Re: [Intel-gfx] [PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Daniel Vetter]

On Wed, Mar 29, 2017 at 03:51:08PM +0200, Maarten Lankhorst wrote:
> Op 29-03-17 om 15:31 schreef Boris Brezillon:
> > On Wed, 29 Mar 2017 15:26:45 +0200
> > Daniel Vetter <daniel@ffwll.ch> wrote:
> >
> >> On Wed, Mar 29, 2017 at 12:16:50PM +0200, Maarten Lankhorst wrote:
> >>> mode_valid() and get_modes() called
> >>> from drm_helper_probe_single_connector_modes()
> >>> may need to look at connector->state because what a valid mode is may
> >>> depend on connector properties being set. For example some HDMI modes
> >>> might be rejected when a connector property forces the connector
> >>> into DVI mode.
> >>>
> >>> Some implementations of detect() already lock all state,
> >>> so we have to pass an acquire_ctx to them to prevent a deadlock.
> >>>
> >>> This means changing the function signature of detect() slightly,
> >>> and passing the acquire_ctx for locking multiple crtc's.
> >>> It might be NULL, in which case expensive operations should be avoided.
> >>>
> >>> intel_dp.c however ignores the force flag, so still lock
> >>> connection_mutex there if needed.
> >>>
> >>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> >>> Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
> >>> Cc: Manasi Navare <manasi.d.navare@intel.com>  
> >> Hm only noticed this now, but mixing up force with the acquire_ctx sounds
> >> like very bad interface design. Yes, the only user of the new hook works
> >> like that, but that's really accidental I think. I think just having the
> >> ctx everywhere (for atomic drivers at least) would be a lot safer. This is
> >> extremely surprising (and undocumented suprise at that).
> > Yes, I was about to say the same thing: the interface is not very
> > clear, and I don't understand why ctx = NULL implies force = false.
> 
> They're the same thing I fear. I could perhaps call it force_ctx instead,
> but non-zero ctx implies force, and other way around. Though I guess we could
> relax it, and have force = true imply ctx, but not the other way around.
> 
> Would that be ok?

Why can't we supply a ctx always? I didn't see any reason not to in the
code ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [Intel-gfx] [PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Maarten Lankhorst]

Op 29-03-17 om 16:06 schreef Daniel Vetter:
> On Wed, Mar 29, 2017 at 03:51:08PM +0200, Maarten Lankhorst wrote:
>> Op 29-03-17 om 15:31 schreef Boris Brezillon:
>>> On Wed, 29 Mar 2017 15:26:45 +0200
>>> Daniel Vetter <daniel@ffwll.ch> wrote:
>>>
>>>> On Wed, Mar 29, 2017 at 12:16:50PM +0200, Maarten Lankhorst wrote:
>>>>> mode_valid() and get_modes() called
>>>>> from drm_helper_probe_single_connector_modes()
>>>>> may need to look at connector->state because what a valid mode is may
>>>>> depend on connector properties being set. For example some HDMI modes
>>>>> might be rejected when a connector property forces the connector
>>>>> into DVI mode.
>>>>>
>>>>> Some implementations of detect() already lock all state,
>>>>> so we have to pass an acquire_ctx to them to prevent a deadlock.
>>>>>
>>>>> This means changing the function signature of detect() slightly,
>>>>> and passing the acquire_ctx for locking multiple crtc's.
>>>>> It might be NULL, in which case expensive operations should be avoided.
>>>>>
>>>>> intel_dp.c however ignores the force flag, so still lock
>>>>> connection_mutex there if needed.
>>>>>
>>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>>>> Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
>>>>> Cc: Manasi Navare <manasi.d.navare@intel.com>  
>>>> Hm only noticed this now, but mixing up force with the acquire_ctx sounds
>>>> like very bad interface design. Yes, the only user of the new hook works
>>>> like that, but that's really accidental I think. I think just having the
>>>> ctx everywhere (for atomic drivers at least) would be a lot safer. This is
>>>> extremely surprising (and undocumented suprise at that).
>>> Yes, I was about to say the same thing: the interface is not very
>>> clear, and I don't understand why ctx = NULL implies force = false.
>> They're the same thing I fear. I could perhaps call it force_ctx instead,
>> but non-zero ctx implies force, and other way around. Though I guess we could
>> relax it, and have force = true imply ctx, but not the other way around.
>>
>> Would that be ok?
> Why can't we supply a ctx always? I didn't see any reason not to in the
> code ...
> -Daniel

Then drm_helper_hpd_irq_event and intel_hpd_irq_event have to do -EDEADLK handling too,
it could be done but nothing would return -EDEADLK so it's unused code.

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