[PATCH] drm: rework delayed connector cleanup in connector_iter

[PATCH] drm: rework delayed connector cleanup in connector_iter

[Daniel Vetter]

PROBE_DEFER also uses system_wq to reprobe drivers, which means when
that again fails, and we try to flush the overall system_wq (to get
all the delayed connectore cleanup work_struct completed), we
deadlock.

Fix this by using just a single cleanup work, so that we can only
flush that one and don't block on anything else. That means a free
list plus locking, a standard pattern.

Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
Cc: <stable@vger.kernel.org> # v4.11+
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Javier Martinez Canillas <javier@dowhile0.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Matt Hart <matthew.hart@linaro.org>
Cc: Thierry Escande <thierry.escande@collabora.co.uk>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_connector.c     | 46 ++++++++++++++++++++++++++-----------
 drivers/gpu/drm/drm_crtc_internal.h |  1 +
 drivers/gpu/drm/drm_mode_config.c   |  5 +++-
 include/drm/drm_connector.h         |  4 ++--
 include/drm/drm_mode_config.h       | 17 +++++++++++++-
 5 files changed, 55 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 0b7e0974e6da..2f43dc217936 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
 	connector->funcs->destroy(connector);
 }
 
-static void drm_connector_free_work_fn(struct work_struct *work)
+void drm_connector_free_work_fn(struct work_struct *work)
 {
-	struct drm_connector *connector =
-		container_of(work, struct drm_connector, free_work);
-	struct drm_device *dev = connector->dev;
+	struct drm_connector *connector;
+	struct drm_device *dev =
+		container_of(work, struct drm_device, mode_config.connector_free_work);
+	struct drm_mode_config *config = &dev->mode_config;
+	unsigned long flags;
+	LIST_HEAD(list_head);
 
-	drm_mode_object_unregister(dev, &connector->base);
-	connector->funcs->destroy(connector);
+	spin_lock_irqsave(&config->connector_list_lock, flags);
+	list_splice(&config->connector_free_list, &list_head);
+	spin_unlock_irqrestore(&config->connector_list_lock, flags);
+
+	list_for_each_entry(connector, &list_head, free_head) {
+		drm_mode_object_unregister(dev, &connector->base);
+		connector->funcs->destroy(connector);
+	}
 }
 
 /**
@@ -192,8 +201,6 @@ int drm_connector_init(struct drm_device *dev,
 	if (ret)
 		return ret;
 
-	INIT_WORK(&connector->free_work, drm_connector_free_work_fn);
-
 	connector->base.properties = &connector->properties;
 	connector->dev = dev;
 	connector->funcs = funcs;
@@ -550,10 +557,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_begin);
  * actually release the connector when dropping our final reference.
  */
 static void
-drm_connector_put_safe(struct drm_connector *conn)
+__drm_connector_put_safe(struct drm_connector *conn)
 {
+	struct drm_mode_config *config = &conn->dev->mode_config;
+
+	lockdep_assert_held(&config->connector_list_lock);
+	list_add(&conn->free_head, &config->connector_free_list);
+
 	if (refcount_dec_and_test(&conn->base.refcount.refcount))
-		schedule_work(&conn->free_work);
+		schedule_work(&config->connector_free_work);
 }
 
 /**
@@ -585,10 +597,10 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter)
 
 		/* loop until it's not a zombie connector */
 	} while (!kref_get_unless_zero(&iter->conn->base.refcount));
-	spin_unlock_irqrestore(&config->connector_list_lock, flags);
 
 	if (old_conn)
-		drm_connector_put_safe(old_conn);
+		__drm_connector_put_safe(old_conn);
+	spin_unlock_irqrestore(&config->connector_list_lock, flags);
 
 	return iter->conn;
 }
@@ -605,9 +617,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_next);
  */
 void drm_connector_list_iter_end(struct drm_connector_list_iter *iter)
 {
+	struct drm_mode_config *config = &iter->dev->mode_config;
+	unsigned long flags;
+
 	iter->dev = NULL;
-	if (iter->conn)
-		drm_connector_put_safe(iter->conn);
+	if (iter->conn) {
+		spin_lock_irqsave(&config->connector_list_lock, flags);
+		__drm_connector_put_safe(iter->conn);
+		spin_unlock_irqrestore(&config->connector_list_lock, flags);
+	}
 	lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);
 }
 EXPORT_SYMBOL(drm_connector_list_iter_end);
diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
index 9ebb8841778c..af00f42ba269 100644
--- a/drivers/gpu/drm/drm_crtc_internal.h
+++ b/drivers/gpu/drm/drm_crtc_internal.h
@@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
 				    uint64_t value);
 int drm_connector_create_standard_properties(struct drm_device *dev);
 const char *drm_get_connector_force_name(enum drm_connector_force force);
+void drm_connector_free_work_fn(struct work_struct *work);
 
 /* IOCTL */
 int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 6ffe952142e6..025fc23cf7c6 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -373,6 +373,7 @@ void drm_mode_config_init(struct drm_device *dev)
 	INIT_LIST_HEAD(&dev->mode_config.fb_list);
 	INIT_LIST_HEAD(&dev->mode_config.crtc_list);
 	INIT_LIST_HEAD(&dev->mode_config.connector_list);
+	INIT_LIST_HEAD(&dev->mode_config.connector_free_list);
 	INIT_LIST_HEAD(&dev->mode_config.encoder_list);
 	INIT_LIST_HEAD(&dev->mode_config.property_list);
 	INIT_LIST_HEAD(&dev->mode_config.property_blob_list);
@@ -382,6 +383,8 @@ void drm_mode_config_init(struct drm_device *dev)
 	ida_init(&dev->mode_config.connector_ida);
 	spin_lock_init(&dev->mode_config.connector_list_lock);
 
+	INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
+
 	drm_mode_create_standard_properties(dev);
 
 	/* Just to be sure */
@@ -432,7 +435,7 @@ void drm_mode_config_cleanup(struct drm_device *dev)
 	}
 	drm_connector_list_iter_end(&conn_iter);
 	/* connector_iter drops references in a work item. */
-	flush_scheduled_work();
+	flush_work(&dev->mode_config.connector_free_work);
 	if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) {
 		drm_connector_list_iter_begin(dev, &conn_iter);
 		drm_for_each_connector_iter(connector, &conn_iter)
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index ee3155391243..50bc21050fbf 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -966,12 +966,12 @@ struct drm_connector {
 	uint16_t tile_h_size, tile_v_size;
 
 	/**
-	 * @free_work:
+	 * @free_head:
 	 *
 	 * Work used only by &drm_connector_iter to be able to clean up a
 	 * connector from any context.
 	 */
-	struct work_struct free_work;
+	struct list_head free_head;
 };
 
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index e5f3b43014e1..5e62e52a2c58 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -402,7 +402,7 @@ struct drm_mode_config {
 
 	/**
 	 * @connector_list_lock: Protects @num_connector and
-	 * @connector_list.
+	 * @connector_list and @connector_free_list.
 	 */
 	spinlock_t connector_list_lock;
 	/**
@@ -422,6 +422,21 @@ struct drm_mode_config {
 	 * &struct drm_connector_list_iter to walk this list.
 	 */
 	struct list_head connector_list;
+	/**
+	 * @connector_free_list:
+	 *
+	 * List of connector objects linked with &drm_connector.free_head.
+	 * Protected by @connector_list_lock. Used by
+	 * drm_for_each_connector_iter() and
+	 * &struct drm_connector_list_iter to savely free connectors using
+	 * @connector_free_work.
+	 */
+	struct list_head connector_free_list;
+	/**
+	 * @connector_free_work: Work to clean up @connector_free_list.
+	 */
+	struct work_struct connector_free_work;
+
 	/**
 	 * @num_encoder:
 	 *
-- 
2.15.1

Re: [PATCH] drm: rework delayed connector cleanup in connector_iter

[Chris Wilson]

Quoting Daniel Vetter (2017-12-13 10:45:53)
> PROBE_DEFER also uses system_wq to reprobe drivers, which means when
> that again fails, and we try to flush the overall system_wq (to get
> all the delayed connectore cleanup work_struct completed), we
> deadlock.
> 
> Fix this by using just a single cleanup work, so that we can only
> flush that one and don't block on anything else. That means a free
> list plus locking, a standard pattern.
> 
> Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Ben Widawsky <ben@bwidawsk.net>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> Cc: <stable@vger.kernel.org> # v4.11+
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Javier Martinez Canillas <javier@dowhile0.org>
> Cc: Shuah Khan <shuahkh@osg.samsung.com>
> Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Kevin Hilman <khilman@baylibre.com>
> Cc: Matt Hart <matthew.hart@linaro.org>
> Cc: Thierry Escande <thierry.escande@collabora.co.uk>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c     | 46 ++++++++++++++++++++++++++-----------
>  drivers/gpu/drm/drm_crtc_internal.h |  1 +
>  drivers/gpu/drm/drm_mode_config.c   |  5 +++-
>  include/drm/drm_connector.h         |  4 ++--
>  include/drm/drm_mode_config.h       | 17 +++++++++++++-
>  5 files changed, 55 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 0b7e0974e6da..2f43dc217936 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
>         connector->funcs->destroy(connector);
>  }
>  
> -static void drm_connector_free_work_fn(struct work_struct *work)
> +void drm_connector_free_work_fn(struct work_struct *work)
>  {
> -       struct drm_connector *connector =
> -               container_of(work, struct drm_connector, free_work);
> -       struct drm_device *dev = connector->dev;
> +       struct drm_connector *connector;
> +       struct drm_device *dev =
> +               container_of(work, struct drm_device, mode_config.connector_free_work);
> +       struct drm_mode_config *config = &dev->mode_config;
> +       unsigned long flags;
> +       LIST_HEAD(list_head);
>  
> -       drm_mode_object_unregister(dev, &connector->base);
> -       connector->funcs->destroy(connector);
> +       spin_lock_irqsave(&config->connector_list_lock, flags);
> +       list_splice(&config->connector_free_list, &list_head);
> +       spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +
> +       list_for_each_entry(connector, &list_head, free_head) {
> +               drm_mode_object_unregister(dev, &connector->base);
> +               connector->funcs->destroy(connector);
> +       }
>  }
>  
>  /**
> @@ -192,8 +201,6 @@ int drm_connector_init(struct drm_device *dev,
>         if (ret)
>                 return ret;
>  
> -       INIT_WORK(&connector->free_work, drm_connector_free_work_fn);
> -
>         connector->base.properties = &connector->properties;
>         connector->dev = dev;
>         connector->funcs = funcs;
> @@ -550,10 +557,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_begin);
>   * actually release the connector when dropping our final reference.
>   */
>  static void
> -drm_connector_put_safe(struct drm_connector *conn)
> +__drm_connector_put_safe(struct drm_connector *conn)
>  {
> +       struct drm_mode_config *config = &conn->dev->mode_config;
> +
> +       lockdep_assert_held(&config->connector_list_lock);
> +       list_add(&conn->free_head, &config->connector_free_list);

Adding to the free_list before refcount==0?

May I suggest,

	if (!refcount_dec_and_test())
		return;

	if (llist_add(&conn->free_link, &config->connector_free_list))
		schedule_work(&config->connector_free_work);

llist being much more friendly for freelists:

void drm_connector_free_work_fn(struct work_struct *work)
{
	struct drm_device *dev =
		container_of(work, struct drm_device, mode_config.connector_free_work);
	struct drm_mode_config *config = &dev->mode_config;
	struct drm_connector *connector, *n;
	struct llist_node *freed;

	freed = llist_del_all(config->connector_free_list);
	llist_for_each_entry_safe(connector, n, freed, free_link) {
		drm_mode_object_unregister(dev, &connector->base);
		connector->funcs->destroy(connector);
	}
}
-Chris

Re: [PATCH] drm: rework delayed connector cleanup in connector_iter

[Marek Szyprowski]

Hi Daniel,

On 2017-12-13 11:45, Daniel Vetter wrote:
> PROBE_DEFER also uses system_wq to reprobe drivers, which means when
> that again fails, and we try to flush the overall system_wq (to get
> all the delayed connectore cleanup work_struct completed), we
> deadlock.
>
> Fix this by using just a single cleanup work, so that we can only
> flush that one and don't block on anything else. That means a free
> list plus locking, a standard pattern.
>
> Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Ben Widawsky <ben@bwidawsk.net>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> Cc: <stable@vger.kernel.org> # v4.11+
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Javier Martinez Canillas <javier@dowhile0.org>
> Cc: Shuah Khan <shuahkh@osg.samsung.com>
> Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Kevin Hilman <khilman@baylibre.com>
> Cc: Matt Hart <matthew.hart@linaro.org>
> Cc: Thierry Escande <thierry.escande@collabora.co.uk>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Sadly, this patch doesn't work in my test environment (Samsung Snow
Chromebook with modified DTS), which reproduces the problem discussed
inhttps://www.spinics.net/lists/arm-kernel/msg622332.html


[    4.925178] exynos-drm exynos-drm: failed to bind 14530000.hdmi (ops 
hdmi_component_ops): -19
[    4.936167] Unable to handle kernel paging request at virtual address 
fffffcac
[    4.942004] pgd = ad8213ad
[    4.944654] [fffffcac] *pgd=6fffd861, *pte=00000000, *ppte=00000000
[    4.950944] Internal error: Oops: 37 [#1] PREEMPT SMP ARM
[    4.956284] Modules linked in:
[    4.959324] CPU: 1 PID: 80 Comm: kworker/1:3 Not tainted 
4.15.0-rc3-next-20171212-00004-g879e6206b6fb-dirty #56
[    4.969391] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[    4.975472] Workqueue: events drm_connector_free_work_fn
[    4.980765] PC is at drm_mode_object_unregister+0x1c/0x48
[    4.986146] LR is at __mutex_lock+0x3ec/0xa0c
[    4.990483] pc : [<c050e744>]    lr : [<c0a0465c>] psr: 60000113
[    4.996731] sp : ed27dec0  ip : ed27c000  fp : ed25042c
[    5.001940] r10: 00000000  r9 : c1008c6c  r8 : c10ae6d4
[    5.007148] r7 : ed2503ec  r6 : ed250000  r5 : fffffcac  r4 : ed250330
[    5.013659] r3 : 00000000  r2 : 00000001  r1 : ed27de50  r0 : 00000000
[    5.020170] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM 
Segment none
[    5.027286] Control: 10c5387d  Table: 4000406a  DAC: 00000051
[    5.033016] Process kworker/1:3 (pid: 80, stack limit = 0x37cd389f)
[    5.039265] Stack: (0xed27dec0 to 0xed27e000)
[    5.043607] dec0: fffffc98 ed27ded0 ed250000 c050d374 ed242f78 
ed242f78 00000001 ed22e200
[    5.051766] dee0: eefc91c0 eefcc500 c10ad21d c0143438 00000001 
00000000 c0143384 c0143534
[    5.059925] df00: 00000001 00000000 c0143384 00000000 edd0ce00 
c181658c c1214a78 00000000
[    5.068084] df20: c0d7c514 00000000 c120f048 ed22e200 ed22e218 
eefc91f8 c0143ae8 c10ae166
[    5.076243] df40: 00000008 ed22e218 c1005d00 c0143a2c eefcc5f5 
ed22e200 eefc91c0 c0143c4c
[    5.084402] df60: c0a09894 ed709100 00000000 ed709100 00000000 
ed25e000 ed709180 ed22e200
[    5.092561] df80: edfdfe68 c0143a3c 00000000 c014a1c4 ed25e000 
c014a074 00000000 00000000
[    5.100720] dfa0: 00000000 00000000 00000000 c01010b4 00000000 
00000000 00000000 00000000
[    5.108879] dfc0: 00000000 00000000 00000000 00000000 00000000 
00000000 00000000 00000000
[    5.117039] dfe0: 00000000 00000000 00000000 00000000 00000013 
00000000 00000000 00000000
[    5.125202] [<c050e744>] (drm_mode_object_unregister) from 
[<c050d374>] (drm_connector_free_work_fn+0x80/0xa8)
[    5.135185] [<c050d374>] (drm_connector_free_work_fn) from 
[<c0143438>] (process_one_work+0x1dc/0x7a8)
[    5.144472] [<c0143438>] (process_one_work) from [<c0143a2c>] 
(process_scheduled_works+0x28/0x38)
[    5.153324] [<c0143a2c>] (process_scheduled_works) from [<c0143c4c>] 
(worker_thread+0x210/0x4dc)
[    5.162092] [<c0143c4c>] (worker_thread) from [<c014a1c4>] 
(kthread+0x150/0x19c)
[    5.169469] [<c014a1c4>] (kthread) from [<c01010b4>] 
(ret_from_fork+0x14/0x20)
[    5.176669] Exception stack(0xed27dfb0 to 0xed27dff8)
[    5.181704] dfa0:                                     00000000 
00000000 00000000 00000000
[    5.189864] dfc0: 00000000 00000000 00000000 00000000 00000000 
00000000 00000000 00000000
[    5.198023] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000
[    5.204622] Code: e1a06000 e3a01000 e1a00004 eb13d968 (e5951000)
[    5.210731] ---[ end trace 55b8b9b30581db4f ]---


I will try to provide a bit more details soon.

> ---
>   drivers/gpu/drm/drm_connector.c     | 46 ++++++++++++++++++++++++++-----------
>   drivers/gpu/drm/drm_crtc_internal.h |  1 +
>   drivers/gpu/drm/drm_mode_config.c   |  5 +++-
>   include/drm/drm_connector.h         |  4 ++--
>   include/drm/drm_mode_config.h       | 17 +++++++++++++-
>   5 files changed, 55 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 0b7e0974e6da..2f43dc217936 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
>   	connector->funcs->destroy(connector);
>   }
>   
> -static void drm_connector_free_work_fn(struct work_struct *work)
> +void drm_connector_free_work_fn(struct work_struct *work)
>   {
> -	struct drm_connector *connector =
> -		container_of(work, struct drm_connector, free_work);
> -	struct drm_device *dev = connector->dev;
> +	struct drm_connector *connector;
> +	struct drm_device *dev =
> +		container_of(work, struct drm_device, mode_config.connector_free_work);
> +	struct drm_mode_config *config = &dev->mode_config;
> +	unsigned long flags;
> +	LIST_HEAD(list_head);
>   
> -	drm_mode_object_unregister(dev, &connector->base);
> -	connector->funcs->destroy(connector);
> +	spin_lock_irqsave(&config->connector_list_lock, flags);
> +	list_splice(&config->connector_free_list, &list_head);
> +	spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +
> +	list_for_each_entry(connector, &list_head, free_head) {
> +		drm_mode_object_unregister(dev, &connector->base);
> +		connector->funcs->destroy(connector);
> +	}
>   }
>   
>   /**
> @@ -192,8 +201,6 @@ int drm_connector_init(struct drm_device *dev,
>   	if (ret)
>   		return ret;
>   
> -	INIT_WORK(&connector->free_work, drm_connector_free_work_fn);
> -
>   	connector->base.properties = &connector->properties;
>   	connector->dev = dev;
>   	connector->funcs = funcs;
> @@ -550,10 +557,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_begin);
>    * actually release the connector when dropping our final reference.
>    */
>   static void
> -drm_connector_put_safe(struct drm_connector *conn)
> +__drm_connector_put_safe(struct drm_connector *conn)
>   {
> +	struct drm_mode_config *config = &conn->dev->mode_config;
> +
> +	lockdep_assert_held(&config->connector_list_lock);
> +	list_add(&conn->free_head, &config->connector_free_list);
> +
>   	if (refcount_dec_and_test(&conn->base.refcount.refcount))
> -		schedule_work(&conn->free_work);
> +		schedule_work(&config->connector_free_work);
>   }
>   
>   /**
> @@ -585,10 +597,10 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter)
>   
>   		/* loop until it's not a zombie connector */
>   	} while (!kref_get_unless_zero(&iter->conn->base.refcount));
> -	spin_unlock_irqrestore(&config->connector_list_lock, flags);
>   
>   	if (old_conn)
> -		drm_connector_put_safe(old_conn);
> +		__drm_connector_put_safe(old_conn);
> +	spin_unlock_irqrestore(&config->connector_list_lock, flags);
>   
>   	return iter->conn;
>   }
> @@ -605,9 +617,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_next);
>    */
>   void drm_connector_list_iter_end(struct drm_connector_list_iter *iter)
>   {
> +	struct drm_mode_config *config = &iter->dev->mode_config;
> +	unsigned long flags;
> +
>   	iter->dev = NULL;
> -	if (iter->conn)
> -		drm_connector_put_safe(iter->conn);
> +	if (iter->conn) {
> +		spin_lock_irqsave(&config->connector_list_lock, flags);
> +		__drm_connector_put_safe(iter->conn);
> +		spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +	}
>   	lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);
>   }
>   EXPORT_SYMBOL(drm_connector_list_iter_end);
> diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
> index 9ebb8841778c..af00f42ba269 100644
> --- a/drivers/gpu/drm/drm_crtc_internal.h
> +++ b/drivers/gpu/drm/drm_crtc_internal.h
> @@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
>   				    uint64_t value);
>   int drm_connector_create_standard_properties(struct drm_device *dev);
>   const char *drm_get_connector_force_name(enum drm_connector_force force);
> +void drm_connector_free_work_fn(struct work_struct *work);
>   
>   /* IOCTL */
>   int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 6ffe952142e6..025fc23cf7c6 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -373,6 +373,7 @@ void drm_mode_config_init(struct drm_device *dev)
>   	INIT_LIST_HEAD(&dev->mode_config.fb_list);
>   	INIT_LIST_HEAD(&dev->mode_config.crtc_list);
>   	INIT_LIST_HEAD(&dev->mode_config.connector_list);
> +	INIT_LIST_HEAD(&dev->mode_config.connector_free_list);
>   	INIT_LIST_HEAD(&dev->mode_config.encoder_list);
>   	INIT_LIST_HEAD(&dev->mode_config.property_list);
>   	INIT_LIST_HEAD(&dev->mode_config.property_blob_list);
> @@ -382,6 +383,8 @@ void drm_mode_config_init(struct drm_device *dev)
>   	ida_init(&dev->mode_config.connector_ida);
>   	spin_lock_init(&dev->mode_config.connector_list_lock);
>   
> +	INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
> +
>   	drm_mode_create_standard_properties(dev);
>   
>   	/* Just to be sure */
> @@ -432,7 +435,7 @@ void drm_mode_config_cleanup(struct drm_device *dev)
>   	}
>   	drm_connector_list_iter_end(&conn_iter);
>   	/* connector_iter drops references in a work item. */
> -	flush_scheduled_work();
> +	flush_work(&dev->mode_config.connector_free_work);
>   	if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) {
>   		drm_connector_list_iter_begin(dev, &conn_iter);
>   		drm_for_each_connector_iter(connector, &conn_iter)
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index ee3155391243..50bc21050fbf 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -966,12 +966,12 @@ struct drm_connector {
>   	uint16_t tile_h_size, tile_v_size;
>   
>   	/**
> -	 * @free_work:
> +	 * @free_head:
>   	 *
>   	 * Work used only by &drm_connector_iter to be able to clean up a
>   	 * connector from any context.
>   	 */
> -	struct work_struct free_work;
> +	struct list_head free_head;
>   };
>   
>   #define obj_to_connector(x) container_of(x, struct drm_connector, base)
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index e5f3b43014e1..5e62e52a2c58 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -402,7 +402,7 @@ struct drm_mode_config {
>   
>   	/**
>   	 * @connector_list_lock: Protects @num_connector and
> -	 * @connector_list.
> +	 * @connector_list and @connector_free_list.
>   	 */
>   	spinlock_t connector_list_lock;
>   	/**
> @@ -422,6 +422,21 @@ struct drm_mode_config {
>   	 * &struct drm_connector_list_iter to walk this list.
>   	 */
>   	struct list_head connector_list;
> +	/**
> +	 * @connector_free_list:
> +	 *
> +	 * List of connector objects linked with &drm_connector.free_head.
> +	 * Protected by @connector_list_lock. Used by
> +	 * drm_for_each_connector_iter() and
> +	 * &struct drm_connector_list_iter to savely free connectors using
> +	 * @connector_free_work.
> +	 */
> +	struct list_head connector_free_list;
> +	/**
> +	 * @connector_free_work: Work to clean up @connector_free_list.
> +	 */
> +	struct work_struct connector_free_work;
> +
>   	/**
>   	 * @num_encoder:
>   	 *

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

[PATCH] drm: rework delayed connector cleanup in connector_iter

[Daniel Vetter]

PROBE_DEFER also uses system_wq to reprobe drivers, which means when
that again fails, and we try to flush the overall system_wq (to get
all the delayed connectore cleanup work_struct completed), we
deadlock.

Fix this by using just a single cleanup work, so that we can only
flush that one and don't block on anything else. That means a free
list plus locking, a standard pattern.

v2:
- Correctly free connectors only on last ref. Oops (Chris).
- use llist_head/node (Chris).

Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
Cc: <stable@vger.kernel.org> # v4.11+
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Javier Martinez Canillas <javier@dowhile0.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Matt Hart <matthew.hart@linaro.org>
Cc: Thierry Escande <thierry.escande@collabora.co.uk>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_connector.c     | 50 ++++++++++++++++++++++++++-----------
 drivers/gpu/drm/drm_crtc_internal.h |  1 +
 drivers/gpu/drm/drm_mode_config.c   |  4 ++-
 include/drm/drm_connector.h         | 10 +++++---
 include/drm/drm_mode_config.h       | 18 ++++++++++++-
 5 files changed, 62 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 0b7e0974e6da..3f53f127e1f2 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
 	connector->funcs->destroy(connector);
 }
 
-static void drm_connector_free_work_fn(struct work_struct *work)
+void drm_connector_free_work_fn(struct work_struct *work)
 {
-	struct drm_connector *connector =
-		container_of(work, struct drm_connector, free_work);
-	struct drm_device *dev = connector->dev;
+	struct drm_connector *connector, *n;
+	struct drm_device *dev =
+		container_of(work, struct drm_device, mode_config.connector_free_work);
+	struct drm_mode_config *config = &dev->mode_config;
+	unsigned long flags;
+	struct llist_node *freed;
 
-	drm_mode_object_unregister(dev, &connector->base);
-	connector->funcs->destroy(connector);
+	spin_lock_irqsave(&config->connector_list_lock, flags);
+	freed = llist_del_all(&config->connector_free_list);
+	spin_unlock_irqrestore(&config->connector_list_lock, flags);
+
+	llist_for_each_entry_safe(connector, n, freed, free_node) {
+		drm_mode_object_unregister(dev, &connector->base);
+		connector->funcs->destroy(connector);
+	}
 }
 
 /**
@@ -192,8 +201,6 @@ int drm_connector_init(struct drm_device *dev,
 	if (ret)
 		return ret;
 
-	INIT_WORK(&connector->free_work, drm_connector_free_work_fn);
-
 	connector->base.properties = &connector->properties;
 	connector->dev = dev;
 	connector->funcs = funcs;
@@ -550,10 +557,17 @@ EXPORT_SYMBOL(drm_connector_list_iter_begin);
  * actually release the connector when dropping our final reference.
  */
 static void
-drm_connector_put_safe(struct drm_connector *conn)
+__drm_connector_put_safe(struct drm_connector *conn)
 {
-	if (refcount_dec_and_test(&conn->base.refcount.refcount))
-		schedule_work(&conn->free_work);
+	struct drm_mode_config *config = &conn->dev->mode_config;
+
+	lockdep_assert_held(&config->connector_list_lock);
+
+	if (!refcount_dec_and_test(&conn->base.refcount.refcount))
+		return;
+
+	llist_add(&conn->free_node, &config->connector_free_list);
+	schedule_work(&config->connector_free_work);
 }
 
 /**
@@ -585,10 +599,10 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter)
 
 		/* loop until it's not a zombie connector */
 	} while (!kref_get_unless_zero(&iter->conn->base.refcount));
-	spin_unlock_irqrestore(&config->connector_list_lock, flags);
 
 	if (old_conn)
-		drm_connector_put_safe(old_conn);
+		__drm_connector_put_safe(old_conn);
+	spin_unlock_irqrestore(&config->connector_list_lock, flags);
 
 	return iter->conn;
 }
@@ -605,9 +619,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_next);
  */
 void drm_connector_list_iter_end(struct drm_connector_list_iter *iter)
 {
+	struct drm_mode_config *config = &iter->dev->mode_config;
+	unsigned long flags;
+
 	iter->dev = NULL;
-	if (iter->conn)
-		drm_connector_put_safe(iter->conn);
+	if (iter->conn) {
+		spin_lock_irqsave(&config->connector_list_lock, flags);
+		__drm_connector_put_safe(iter->conn);
+		spin_unlock_irqrestore(&config->connector_list_lock, flags);
+	}
 	lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);
 }
 EXPORT_SYMBOL(drm_connector_list_iter_end);
diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
index 9ebb8841778c..af00f42ba269 100644
--- a/drivers/gpu/drm/drm_crtc_internal.h
+++ b/drivers/gpu/drm/drm_crtc_internal.h
@@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
 				    uint64_t value);
 int drm_connector_create_standard_properties(struct drm_device *dev);
 const char *drm_get_connector_force_name(enum drm_connector_force force);
+void drm_connector_free_work_fn(struct work_struct *work);
 
 /* IOCTL */
 int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 6ffe952142e6..7681269abe41 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -382,6 +382,8 @@ void drm_mode_config_init(struct drm_device *dev)
 	ida_init(&dev->mode_config.connector_ida);
 	spin_lock_init(&dev->mode_config.connector_list_lock);
 
+	INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
+
 	drm_mode_create_standard_properties(dev);
 
 	/* Just to be sure */
@@ -432,7 +434,7 @@ void drm_mode_config_cleanup(struct drm_device *dev)
 	}
 	drm_connector_list_iter_end(&conn_iter);
 	/* connector_iter drops references in a work item. */
-	flush_scheduled_work();
+	flush_work(&dev->mode_config.connector_free_work);
 	if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) {
 		drm_connector_list_iter_begin(dev, &conn_iter);
 		drm_for_each_connector_iter(connector, &conn_iter)
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index ee3155391243..ed38df4ac204 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -24,6 +24,7 @@
 #define __DRM_CONNECTOR_H__
 
 #include <linux/list.h>
+#include <linux/llist.h>
 #include <linux/ctype.h>
 #include <linux/hdmi.h>
 #include <drm/drm_mode_object.h>
@@ -966,12 +967,13 @@ struct drm_connector {
 	uint16_t tile_h_size, tile_v_size;
 
 	/**
-	 * @free_work:
+	 * @free_node:
 	 *
-	 * Work used only by &drm_connector_iter to be able to clean up a
-	 * connector from any context.
+	 * List used only by &drm_connector_iter to be able to clean up a
+	 * connector from any context, in conjunction with
+	 * &drm_mode_config.connector_free_work.
 	 */
-	struct work_struct free_work;
+	struct llist_node free_node;
 };
 
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index e5f3b43014e1..2cb6f02df64a 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -27,6 +27,7 @@
 #include <linux/types.h>
 #include <linux/idr.h>
 #include <linux/workqueue.h>
+#include <linux/llist.h>
 
 #include <drm/drm_modeset_lock.h>
 
@@ -402,7 +403,7 @@ struct drm_mode_config {
 
 	/**
 	 * @connector_list_lock: Protects @num_connector and
-	 * @connector_list.
+	 * @connector_list and @connector_free_list.
 	 */
 	spinlock_t connector_list_lock;
 	/**
@@ -422,6 +423,21 @@ struct drm_mode_config {
 	 * &struct drm_connector_list_iter to walk this list.
 	 */
 	struct list_head connector_list;
+	/**
+	 * @connector_free_list:
+	 *
+	 * List of connector objects linked with &drm_connector.free_head.
+	 * Protected by @connector_list_lock. Used by
+	 * drm_for_each_connector_iter() and
+	 * &struct drm_connector_list_iter to savely free connectors using
+	 * @connector_free_work.
+	 */
+	struct llist_head connector_free_list;
+	/**
+	 * @connector_free_work: Work to clean up @connector_free_list.
+	 */
+	struct work_struct connector_free_work;
+
 	/**
 	 * @num_encoder:
 	 *
-- 
2.15.1

Re: [PATCH] drm: rework delayed connector cleanup in connector_iter

[Marek Szyprowski]

Hi Daniel,

On 2017-12-13 13:49, Daniel Vetter wrote:
> PROBE_DEFER also uses system_wq to reprobe drivers, which means when
> that again fails, and we try to flush the overall system_wq (to get
> all the delayed connectore cleanup work_struct completed), we
> deadlock.
>
> Fix this by using just a single cleanup work, so that we can only
> flush that one and don't block on anything else. That means a free
> list plus locking, a standard pattern.
>
> v2:
> - Correctly free connectors only on last ref. Oops (Chris).
> - use llist_head/node (Chris).
>
> Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Ben Widawsky <ben@bwidawsk.net>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> Cc: <stable@vger.kernel.org> # v4.11+
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Javier Martinez Canillas <javier@dowhile0.org>
> Cc: Shuah Khan <shuahkh@osg.samsung.com>
> Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Kevin Hilman <khilman@baylibre.com>
> Cc: Matt Hart <matthew.hart@linaro.org>
> Cc: Thierry Escande <thierry.escande@collabora.co.uk>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

This one works fine and fixes deadlock in my test environment.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---
>   drivers/gpu/drm/drm_connector.c     | 50 ++++++++++++++++++++++++++-----------
>   drivers/gpu/drm/drm_crtc_internal.h |  1 +
>   drivers/gpu/drm/drm_mode_config.c   |  4 ++-
>   include/drm/drm_connector.h         | 10 +++++---
>   include/drm/drm_mode_config.h       | 18 ++++++++++++-
>   5 files changed, 62 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 0b7e0974e6da..3f53f127e1f2 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
>   	connector->funcs->destroy(connector);
>   }
>   
> -static void drm_connector_free_work_fn(struct work_struct *work)
> +void drm_connector_free_work_fn(struct work_struct *work)
>   {
> -	struct drm_connector *connector =
> -		container_of(work, struct drm_connector, free_work);
> -	struct drm_device *dev = connector->dev;
> +	struct drm_connector *connector, *n;
> +	struct drm_device *dev =
> +		container_of(work, struct drm_device, mode_config.connector_free_work);
> +	struct drm_mode_config *config = &dev->mode_config;
> +	unsigned long flags;
> +	struct llist_node *freed;
>   
> -	drm_mode_object_unregister(dev, &connector->base);
> -	connector->funcs->destroy(connector);
> +	spin_lock_irqsave(&config->connector_list_lock, flags);
> +	freed = llist_del_all(&config->connector_free_list);
> +	spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +
> +	llist_for_each_entry_safe(connector, n, freed, free_node) {
> +		drm_mode_object_unregister(dev, &connector->base);
> +		connector->funcs->destroy(connector);
> +	}
>   }
>   
>   /**
> @@ -192,8 +201,6 @@ int drm_connector_init(struct drm_device *dev,
>   	if (ret)
>   		return ret;
>   
> -	INIT_WORK(&connector->free_work, drm_connector_free_work_fn);
> -
>   	connector->base.properties = &connector->properties;
>   	connector->dev = dev;
>   	connector->funcs = funcs;
> @@ -550,10 +557,17 @@ EXPORT_SYMBOL(drm_connector_list_iter_begin);
>    * actually release the connector when dropping our final reference.
>    */
>   static void
> -drm_connector_put_safe(struct drm_connector *conn)
> +__drm_connector_put_safe(struct drm_connector *conn)
>   {
> -	if (refcount_dec_and_test(&conn->base.refcount.refcount))
> -		schedule_work(&conn->free_work);
> +	struct drm_mode_config *config = &conn->dev->mode_config;
> +
> +	lockdep_assert_held(&config->connector_list_lock);
> +
> +	if (!refcount_dec_and_test(&conn->base.refcount.refcount))
> +		return;
> +
> +	llist_add(&conn->free_node, &config->connector_free_list);
> +	schedule_work(&config->connector_free_work);
>   }
>   
>   /**
> @@ -585,10 +599,10 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter)
>   
>   		/* loop until it's not a zombie connector */
>   	} while (!kref_get_unless_zero(&iter->conn->base.refcount));
> -	spin_unlock_irqrestore(&config->connector_list_lock, flags);
>   
>   	if (old_conn)
> -		drm_connector_put_safe(old_conn);
> +		__drm_connector_put_safe(old_conn);
> +	spin_unlock_irqrestore(&config->connector_list_lock, flags);
>   
>   	return iter->conn;
>   }
> @@ -605,9 +619,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_next);
>    */
>   void drm_connector_list_iter_end(struct drm_connector_list_iter *iter)
>   {
> +	struct drm_mode_config *config = &iter->dev->mode_config;
> +	unsigned long flags;
> +
>   	iter->dev = NULL;
> -	if (iter->conn)
> -		drm_connector_put_safe(iter->conn);
> +	if (iter->conn) {
> +		spin_lock_irqsave(&config->connector_list_lock, flags);
> +		__drm_connector_put_safe(iter->conn);
> +		spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +	}
>   	lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);
>   }
>   EXPORT_SYMBOL(drm_connector_list_iter_end);
> diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
> index 9ebb8841778c..af00f42ba269 100644
> --- a/drivers/gpu/drm/drm_crtc_internal.h
> +++ b/drivers/gpu/drm/drm_crtc_internal.h
> @@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
>   				    uint64_t value);
>   int drm_connector_create_standard_properties(struct drm_device *dev);
>   const char *drm_get_connector_force_name(enum drm_connector_force force);
> +void drm_connector_free_work_fn(struct work_struct *work);
>   
>   /* IOCTL */
>   int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 6ffe952142e6..7681269abe41 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -382,6 +382,8 @@ void drm_mode_config_init(struct drm_device *dev)
>   	ida_init(&dev->mode_config.connector_ida);
>   	spin_lock_init(&dev->mode_config.connector_list_lock);
>   
> +	INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
> +
>   	drm_mode_create_standard_properties(dev);
>   
>   	/* Just to be sure */
> @@ -432,7 +434,7 @@ void drm_mode_config_cleanup(struct drm_device *dev)
>   	}
>   	drm_connector_list_iter_end(&conn_iter);
>   	/* connector_iter drops references in a work item. */
> -	flush_scheduled_work();
> +	flush_work(&dev->mode_config.connector_free_work);
>   	if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) {
>   		drm_connector_list_iter_begin(dev, &conn_iter);
>   		drm_for_each_connector_iter(connector, &conn_iter)
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index ee3155391243..ed38df4ac204 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -24,6 +24,7 @@
>   #define __DRM_CONNECTOR_H__
>   
>   #include <linux/list.h>
> +#include <linux/llist.h>
>   #include <linux/ctype.h>
>   #include <linux/hdmi.h>
>   #include <drm/drm_mode_object.h>
> @@ -966,12 +967,13 @@ struct drm_connector {
>   	uint16_t tile_h_size, tile_v_size;
>   
>   	/**
> -	 * @free_work:
> +	 * @free_node:
>   	 *
> -	 * Work used only by &drm_connector_iter to be able to clean up a
> -	 * connector from any context.
> +	 * List used only by &drm_connector_iter to be able to clean up a
> +	 * connector from any context, in conjunction with
> +	 * &drm_mode_config.connector_free_work.
>   	 */
> -	struct work_struct free_work;
> +	struct llist_node free_node;
>   };
>   
>   #define obj_to_connector(x) container_of(x, struct drm_connector, base)
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index e5f3b43014e1..2cb6f02df64a 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -27,6 +27,7 @@
>   #include <linux/types.h>
>   #include <linux/idr.h>
>   #include <linux/workqueue.h>
> +#include <linux/llist.h>
>   
>   #include <drm/drm_modeset_lock.h>
>   
> @@ -402,7 +403,7 @@ struct drm_mode_config {
>   
>   	/**
>   	 * @connector_list_lock: Protects @num_connector and
> -	 * @connector_list.
> +	 * @connector_list and @connector_free_list.
>   	 */
>   	spinlock_t connector_list_lock;
>   	/**
> @@ -422,6 +423,21 @@ struct drm_mode_config {
>   	 * &struct drm_connector_list_iter to walk this list.
>   	 */
>   	struct list_head connector_list;
> +	/**
> +	 * @connector_free_list:
> +	 *
> +	 * List of connector objects linked with &drm_connector.free_head.
> +	 * Protected by @connector_list_lock. Used by
> +	 * drm_for_each_connector_iter() and
> +	 * &struct drm_connector_list_iter to savely free connectors using
> +	 * @connector_free_work.
> +	 */
> +	struct llist_head connector_free_list;
> +	/**
> +	 * @connector_free_work: Work to clean up @connector_free_list.
> +	 */
> +	struct work_struct connector_free_work;
> +
>   	/**
>   	 * @num_encoder:
>   	 *

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH] drm: rework delayed connector cleanup in connector_iter

[Chris Wilson]

Quoting Daniel Vetter (2017-12-13 12:49:36)
> PROBE_DEFER also uses system_wq to reprobe drivers, which means when
> that again fails, and we try to flush the overall system_wq (to get
> all the delayed connectore cleanup work_struct completed), we
> deadlock.
> 
> Fix this by using just a single cleanup work, so that we can only
> flush that one and don't block on anything else. That means a free
> list plus locking, a standard pattern.
> 
> v2:
> - Correctly free connectors only on last ref. Oops (Chris).
> - use llist_head/node (Chris).
> 
> Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Ben Widawsky <ben@bwidawsk.net>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> Cc: <stable@vger.kernel.org> # v4.11+
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Gustavo Padovan <gustavo@padovan.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Javier Martinez Canillas <javier@dowhile0.org>
> Cc: Shuah Khan <shuahkh@osg.samsung.com>
> Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Kevin Hilman <khilman@baylibre.com>
> Cc: Matt Hart <matthew.hart@linaro.org>
> Cc: Thierry Escande <thierry.escande@collabora.co.uk>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c     | 50 ++++++++++++++++++++++++++-----------
>  drivers/gpu/drm/drm_crtc_internal.h |  1 +
>  drivers/gpu/drm/drm_mode_config.c   |  4 ++-
>  include/drm/drm_connector.h         | 10 +++++---
>  include/drm/drm_mode_config.h       | 18 ++++++++++++-
>  5 files changed, 62 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 0b7e0974e6da..3f53f127e1f2 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
>         connector->funcs->destroy(connector);
>  }
>  
> -static void drm_connector_free_work_fn(struct work_struct *work)
> +void drm_connector_free_work_fn(struct work_struct *work)
>  {
> -       struct drm_connector *connector =
> -               container_of(work, struct drm_connector, free_work);
> -       struct drm_device *dev = connector->dev;
> +       struct drm_connector *connector, *n;
> +       struct drm_device *dev =
> +               container_of(work, struct drm_device, mode_config.connector_free_work);
> +       struct drm_mode_config *config = &dev->mode_config;
> +       unsigned long flags;
> +       struct llist_node *freed;
>  
> -       drm_mode_object_unregister(dev, &connector->base);
> -       connector->funcs->destroy(connector);
> +       spin_lock_irqsave(&config->connector_list_lock, flags);
> +       freed = llist_del_all(&config->connector_free_list);
> +       spin_unlock_irqrestore(&config->connector_list_lock, flags);

My understanding is that the spinlock here is only used to guard the
free_list. (It's not protecting the final refcount.) In which case it is
redundant as llist_del_all/llist_add are a safe lockless combination.

That just makes the patch bigger than has to be, but it looks correct.

> +__drm_connector_put_safe(struct drm_connector *conn)
>  {
> -       if (refcount_dec_and_test(&conn->base.refcount.refcount))
> -               schedule_work(&conn->free_work);
> +       struct drm_mode_config *config = &conn->dev->mode_config;
> +
> +       lockdep_assert_held(&config->connector_list_lock);
> +
> +       if (!refcount_dec_and_test(&conn->base.refcount.refcount))
> +               return;
> +
> +       llist_add(&conn->free_node, &config->connector_free_list);
> +       schedule_work(&config->connector_free_work);

(Didn't like the if (llist_add) nano-optimisation? :)

> diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
> index 9ebb8841778c..af00f42ba269 100644
> --- a/drivers/gpu/drm/drm_crtc_internal.h
> +++ b/drivers/gpu/drm/drm_crtc_internal.h
> @@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
>                                     uint64_t value);
>  int drm_connector_create_standard_properties(struct drm_device *dev);
>  const char *drm_get_connector_force_name(enum drm_connector_force force);
> +void drm_connector_free_work_fn(struct work_struct *work);
>  
>  /* IOCTL */
>  int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 6ffe952142e6..7681269abe41 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -382,6 +382,8 @@ void drm_mode_config_init(struct drm_device *dev)
>         ida_init(&dev->mode_config.connector_ida);
>         spin_lock_init(&dev->mode_config.connector_list_lock);
>  
> +       INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);

A init_llist_head(&dev->mode_config.connector_free_list) wouldn't go
amiss here. So perhaps push the connectors init into its own exported
function from drm_connector.c as opposed to exposing the free_fn.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

Re: [PATCH] drm: rework delayed connector cleanup in connector_iter

[Daniel Vetter]

On Wed, Dec 13, 2017 at 01:05:49PM +0000, Chris Wilson wrote:
> Quoting Daniel Vetter (2017-12-13 12:49:36)
> > PROBE_DEFER also uses system_wq to reprobe drivers, which means when
> > that again fails, and we try to flush the overall system_wq (to get
> > all the delayed connectore cleanup work_struct completed), we
> > deadlock.
> > 
> > Fix this by using just a single cleanup work, so that we can only
> > flush that one and don't block on anything else. That means a free
> > list plus locking, a standard pattern.
> > 
> > v2:
> > - Correctly free connectors only on last ref. Oops (Chris).
> > - use llist_head/node (Chris).
> > 
> > Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> > Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> > Cc: Ben Widawsky <ben@bwidawsk.net>
> > Cc: Dave Airlie <airlied@gmail.com>
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Sean Paul <seanpaul@chromium.org>
> > Cc: <stable@vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> > Cc: <stable@vger.kernel.org> # v4.11+
> > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Cc: Gustavo Padovan <gustavo@padovan.org>
> > Cc: David Airlie <airlied@linux.ie>
> > Cc: Javier Martinez Canillas <javier@dowhile0.org>
> > Cc: Shuah Khan <shuahkh@osg.samsung.com>
> > Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
> > Cc: Mark Brown <broonie@kernel.org>
> > Cc: Kevin Hilman <khilman@baylibre.com>
> > Cc: Matt Hart <matthew.hart@linaro.org>
> > Cc: Thierry Escande <thierry.escande@collabora.co.uk>
> > Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> > Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >  drivers/gpu/drm/drm_connector.c     | 50 ++++++++++++++++++++++++++-----------
> >  drivers/gpu/drm/drm_crtc_internal.h |  1 +
> >  drivers/gpu/drm/drm_mode_config.c   |  4 ++-
> >  include/drm/drm_connector.h         | 10 +++++---
> >  include/drm/drm_mode_config.h       | 18 ++++++++++++-
> >  5 files changed, 62 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > index 0b7e0974e6da..3f53f127e1f2 100644
> > --- a/drivers/gpu/drm/drm_connector.c
> > +++ b/drivers/gpu/drm/drm_connector.c
> > @@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
> >         connector->funcs->destroy(connector);
> >  }
> >  
> > -static void drm_connector_free_work_fn(struct work_struct *work)
> > +void drm_connector_free_work_fn(struct work_struct *work)
> >  {
> > -       struct drm_connector *connector =
> > -               container_of(work, struct drm_connector, free_work);
> > -       struct drm_device *dev = connector->dev;
> > +       struct drm_connector *connector, *n;
> > +       struct drm_device *dev =
> > +               container_of(work, struct drm_device, mode_config.connector_free_work);
> > +       struct drm_mode_config *config = &dev->mode_config;
> > +       unsigned long flags;
> > +       struct llist_node *freed;
> >  
> > -       drm_mode_object_unregister(dev, &connector->base);
> > -       connector->funcs->destroy(connector);
> > +       spin_lock_irqsave(&config->connector_list_lock, flags);
> > +       freed = llist_del_all(&config->connector_free_list);
> > +       spin_unlock_irqrestore(&config->connector_list_lock, flags);
> 
> My understanding is that the spinlock here is only used to guard the
> free_list. (It's not protecting the final refcount.) In which case it is
> redundant as llist_del_all/llist_add are a safe lockless combination.
> 
> That just makes the patch bigger than has to be, but it looks correct.
> 
> > +__drm_connector_put_safe(struct drm_connector *conn)
> >  {
> > -       if (refcount_dec_and_test(&conn->base.refcount.refcount))
> > -               schedule_work(&conn->free_work);
> > +       struct drm_mode_config *config = &conn->dev->mode_config;
> > +
> > +       lockdep_assert_held(&config->connector_list_lock);
> > +
> > +       if (!refcount_dec_and_test(&conn->base.refcount.refcount))
> > +               return;
> > +
> > +       llist_add(&conn->free_node, &config->connector_free_list);
> > +       schedule_work(&config->connector_free_work);
> 
> (Didn't like the if (llist_add) nano-optimisation? :)

I thought that one might race, since the schedule_work is what provides the
crucial barrier here. But then I was kinda too lazy to read all the llist
guarantees already and just figured I'll keep the spin_lock stuck around
everything.

But yeah it's all neatly lockless, now I'm tempted to redo it all. If CI
spots something I'll include it in the respin for sure.

> > diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
> > index 9ebb8841778c..af00f42ba269 100644
> > --- a/drivers/gpu/drm/drm_crtc_internal.h
> > +++ b/drivers/gpu/drm/drm_crtc_internal.h
> > @@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
> >                                     uint64_t value);
> >  int drm_connector_create_standard_properties(struct drm_device *dev);
> >  const char *drm_get_connector_force_name(enum drm_connector_force force);
> > +void drm_connector_free_work_fn(struct work_struct *work);
> >  
> >  /* IOCTL */
> >  int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
> > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > index 6ffe952142e6..7681269abe41 100644
> > --- a/drivers/gpu/drm/drm_mode_config.c
> > +++ b/drivers/gpu/drm/drm_mode_config.c
> > @@ -382,6 +382,8 @@ void drm_mode_config_init(struct drm_device *dev)
> >         ida_init(&dev->mode_config.connector_ida);
> >         spin_lock_init(&dev->mode_config.connector_list_lock);
> >  
> > +       INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
> 
> A init_llist_head(&dev->mode_config.connector_free_list) wouldn't go
> amiss here. So perhaps push the connectors init into its own exported
> function from drm_connector.c as opposed to exposing the free_fn.

Imo it doesn't matter much how we go about drm.ko internals. But I'll
stick the init_llist_head in there when applying, somehow I dind't find it
(why is every kernel data type slightly different in this).

> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH] drm: rework delayed connector cleanup in connector_iter

[Daniel Vetter]

On Wed, Dec 13, 2017 at 02:35:16PM +0100, Daniel Vetter wrote:
> On Wed, Dec 13, 2017 at 01:05:49PM +0000, Chris Wilson wrote:
> > Quoting Daniel Vetter (2017-12-13 12:49:36)
> > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > > index 6ffe952142e6..7681269abe41 100644
> > > --- a/drivers/gpu/drm/drm_mode_config.c
> > > +++ b/drivers/gpu/drm/drm_mode_config.c
> > > @@ -382,6 +382,8 @@ void drm_mode_config_init(struct drm_device *dev)
> > >         ida_init(&dev->mode_config.connector_ida);
> > >         spin_lock_init(&dev->mode_config.connector_list_lock);
> > >  
> > > +       INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
> > 
> > A init_llist_head(&dev->mode_config.connector_free_list) wouldn't go
> > amiss here. So perhaps push the connectors init into its own exported
> > function from drm_connector.c as opposed to exposing the free_fn.
> 
> Imo it doesn't matter much how we go about drm.ko internals. But I'll
> stick the init_llist_head in there when applying, somehow I dind't find it
> (why is every kernel data type slightly different in this).
> 
> > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

And applied with init_llist_head added.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch