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

[Marek Szyprowski <m.szyprowski@samsung.com>]

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