drm: Use srcu to protect drm_device.unplugged

PATCH In review Oleksandr Andrushchenko 3 participants 6 messages Mar 28, 2018 – Mar 29, 2018

Subsystems (2)

DRM drivers DRM misc

lore

Share & tools

lore

Oleksandr Andrushchenko

author

2018-03-28 07:38 UTC #0 lore raw

PATCH 1/1 drm: Use srcu to protect drm_device.unplugged

From: Noralf Trønnes <[email protected]>

Use srcu to protect drm_device.unplugged in a race free manner. Drivers can use drm_dev_enter()/drm_dev_exit() to protect and mark sections preventing access to device resources that are not available after the device is gone.

Signed-off-by Noralf Trønnes <[email protected]>

Signed-off-by Oleksandr Andrushchenko <[email protected]>

Reviewed-by Oleksandr Andrushchenko <[email protected]>

Tested-by Oleksandr Andrushchenko <[email protected]>

Cc [email protected]

---
 drivers/gpu/drm/drm_drv.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
 include/drm/drm_device.h  |  9 +++++++-
 include/drm/drm_drv.h     | 15 +++++++++----
 3 files changed, 68 insertions(+), 10 deletions(-)

drivers/gpu/drm/drm_drv.c +49 -5

index a1b9338736e3..32a83b41ab61 100644
@@ -32,6 +32,7 @@
 #include <linux/moduleparam.h>
 #include <linux/mount.h>
 #include <linux/slab.h>
+#include <linux/srcu.h>
 
 #include <drm/drm_drv.h>
 #include <drm/drmP.h>

@@ -75,6 +76,8 @@ static bool drm_core_init_complete = false;
 
 static struct dentry *drm_debugfs_root;
 
+DEFINE_STATIC_SRCU(drm_unplug_srcu);
+
 /*
  * DRM Minors
  * A DRM device can provide several char-dev interfaces on the DRM-Major. Each

@@ -318,18 +321,51 @@ void drm_put_dev(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_put_dev);
 
-static void drm_device_set_unplugged(struct drm_device *dev)
+/**
+ * drm_dev_enter - Enter device critical section
+ * @dev: DRM device
+ * @idx: Pointer to index that will be passed to the matching drm_dev_exit()
+ *
+ * This function marks and protects the beginning of a section that should not
+ * be entered after the device has been unplugged. The section end is marked
+ * with drm_dev_exit(). Calls to this function can be nested.
+ *
+ * Returns:
+ * True if it is OK to enter the section, false otherwise.
+ */
+bool drm_dev_enter(struct drm_device *dev, int *idx)
+{
+	*idx = srcu_read_lock(&drm_unplug_srcu);
+
+	if (dev->unplugged) {
+		srcu_read_unlock(&drm_unplug_srcu, *idx);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(drm_dev_enter);
+
+/**
+ * drm_dev_exit - Exit device critical section
+ * @idx: index returned from drm_dev_enter()
+ *
+ * This function marks the end of a section that should not be entered after
+ * the device has been unplugged.
+ */
+void drm_dev_exit(int idx)
 {
-	smp_wmb();
-	atomic_set(&dev->unplugged, 1);
+	srcu_read_unlock(&drm_unplug_srcu, idx);
 }
+EXPORT_SYMBOL(drm_dev_exit);
 
 /**
  * drm_dev_unplug - unplug a DRM device
  * @dev: DRM device
  *
  * This unplugs a hotpluggable DRM device, which makes it inaccessible to
- * userspace operations. Entry-points can use drm_dev_is_unplugged(). This
+ * userspace operations. Entry-points can use drm_dev_enter() and
+ * drm_dev_exit() to protect device resources in a race free manner. This
  * essentially unregisters the device like drm_dev_unregister(), but can be
  * called while there are still open users of @dev.
  */

@@ -338,10 +374,18 @@ void drm_dev_unplug(struct drm_device *dev)
 	drm_dev_unregister(dev);
 
 	mutex_lock(&drm_global_mutex);
-	drm_device_set_unplugged(dev);
 	if (dev->open_count == 0)
 		drm_dev_put(dev);
 	mutex_unlock(&drm_global_mutex);
+
+	/*
+	 * After synchronizing any critical read section is guaranteed to see
+	 * the new value of ->unplugged, and any critical section which might
+	 * still have seen the old value of ->unplugged is guaranteed to have
+	 * finished.
+	 */
+	dev->unplugged = true;
+	synchronize_srcu(&drm_unplug_srcu);
 }
 EXPORT_SYMBOL(drm_dev_unplug);

include/drm/drm_device.h +8 -1

index 7c4fa32f3fc6..3a0eac2885b7 100644
@@ -46,7 +46,14 @@ struct drm_device {
 	/* currently active master for this device. Protected by master_mutex */
 	struct drm_master *master;
 
-	atomic_t unplugged;			/**< Flag whether dev is dead */
+	/**
+	 * @unplugged:
+	 *
+	 * Flag to tell if the device has been unplugged.
+	 * See drm_dev_enter() and drm_dev_is_unplugged().
+	 */
+	bool unplugged;
+
 	struct inode *anon_inode;		/**< inode for private address-space */
 	char *unique;				/**< unique name of the device */
 	/*@} */

include/drm/drm_drv.h +11 -4

index d23dcdd1bd95..7e545f5f94d3 100644
@@ -624,6 +624,8 @@ void drm_dev_get(struct drm_device *dev);
 void drm_dev_put(struct drm_device *dev);
 void drm_dev_unref(struct drm_device *dev);
 void drm_put_dev(struct drm_device *dev);
+bool drm_dev_enter(struct drm_device *dev, int *idx);
+void drm_dev_exit(int idx);
 void drm_dev_unplug(struct drm_device *dev);
 
 /**

@@ -635,11 +637,16 @@ void drm_dev_unplug(struct drm_device *dev);
  * unplugged, these two functions guarantee that any store before calling
  * drm_dev_unplug() is visible to callers of this function after it completes
  */
-static inline int drm_dev_is_unplugged(struct drm_device *dev)
+static inline bool drm_dev_is_unplugged(struct drm_device *dev)
 {
-	int ret = atomic_read(&dev->unplugged);
-	smp_rmb();
-	return ret;
+	int idx;
+
+	if (drm_dev_enter(dev, &idx)) {
+		drm_dev_exit(idx);
+		return false;
+	}
+
+	return true;
 }

Signature · 6 lines

2.7.4

_______________________________________________
Intel-gfx mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Patchwork

2018-03-28 07:54 UTC #1 lore raw

✗ Fi.CI.SPARSE: warning for drm: Use srcu to protect drm_device.unplugged

== Series Details ==

Series: drm: Use srcu to protect drm_device.unplugged
URL : https://patchwork.freedesktop.org/series/40793/
State : warning

== Summary ==

$ dim sparse origin/drm-tip
Commit: drm: Use srcu to protect drm_device.unplugged
+drivers/gpu/drm/drm_drv.c:336:6: warning: context imbalance in 'drm_dev_enter' - different lock contexts for basic block
+drivers/gpu/drm/drm_drv.c:356:6: warning: context imbalance in 'drm_dev_exit' - unexpected unlock

_______________________________________________
Intel-gfx mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Patchwork

2018-03-28 08:08 UTC #2 lore raw

✓ Fi.CI.BAT: success for drm: Use srcu to protect drm_device.unplugged

In reply to Oleksandr Andrushchenko

== Series Details ==

Series: drm: Use srcu to protect drm_device.unplugged
URL : https://patchwork.freedesktop.org/series/40793/
State : success

== Summary ==

Series 40793v1 drm: Use srcu to protect drm_device.unplugged
https://patchwork.freedesktop.org/api/1.0/series/40793/revisions/1/mbox/

---- Known issues:

Test debugfs_test:

        Subgroup read_all_entries:
                pass       -> INCOMPLETE (fi-snb-2520m) fdo#103713
Test kms_pipe_crc_basic:
        Subgroup read-crc-pipe-b-frame-sequence:
                pass       -> FAIL       (fi-skl-guc) fdo#103191
        Subgroup suspend-read-crc-pipe-c:
                pass       -> INCOMPLETE (fi-bxt-dsi) fdo#103927
Test prime_vgem:
        Subgroup basic-fence-flip:
                pass       -> FAIL       (fi-ilk-650) fdo#104008

fdo#103713 https://bugs.freedesktop.org/show_bug.cgi?id=103713
fdo#103191 https://bugs.freedesktop.org/show_bug.cgi?id=103191
fdo#103927 https://bugs.freedesktop.org/show_bug.cgi?id=103927
fdo#104008 https://bugs.freedesktop.org/show_bug.cgi?id=104008

fi-bdw-5557u     total:285  pass:264  dwarn:0   dfail:0   fail:0   skip:21  time:432s
fi-bdw-gvtdvm    total:285  pass:261  dwarn:0   dfail:0   fail:0   skip:24  time:439s
fi-blb-e6850     total:285  pass:220  dwarn:1   dfail:0   fail:0   skip:64  time:379s
fi-bsw-n3050     total:285  pass:239  dwarn:0   dfail:0   fail:0   skip:46  time:545s
fi-bwr-2160      total:285  pass:180  dwarn:0   dfail:0   fail:0   skip:105 time:297s
fi-bxt-dsi       total:243  pass:216  dwarn:0   dfail:0   fail:0   skip:26 
fi-bxt-j4205     total:285  pass:256  dwarn:0   dfail:0   fail:0   skip:29  time:521s
fi-byt-j1900     total:285  pass:250  dwarn:0   dfail:0   fail:0   skip:35  time:523s
fi-byt-n2820     total:285  pass:246  dwarn:0   dfail:0   fail:0   skip:39  time:519s
fi-cfl-8700k     total:285  pass:257  dwarn:0   dfail:0   fail:0   skip:28  time:414s
fi-cfl-s3        total:285  pass:259  dwarn:0   dfail:0   fail:0   skip:26  time:571s
fi-cfl-u         total:285  pass:259  dwarn:0   dfail:0   fail:0   skip:26  time:512s
fi-cnl-y3        total:285  pass:259  dwarn:0   dfail:0   fail:0   skip:26  time:590s
fi-elk-e7500     total:285  pass:225  dwarn:1   dfail:0   fail:0   skip:59  time:426s
fi-gdg-551       total:285  pass:177  dwarn:0   dfail:0   fail:0   skip:108 time:323s
fi-glk-1         total:285  pass:257  dwarn:0   dfail:0   fail:0   skip:28  time:541s
fi-hsw-4770      total:285  pass:258  dwarn:0   dfail:0   fail:0   skip:27  time:405s
fi-ilk-650       total:285  pass:224  dwarn:0   dfail:0   fail:1   skip:60  time:420s
fi-ivb-3520m     total:285  pass:256  dwarn:0   dfail:0   fail:0   skip:29  time:476s
fi-ivb-3770      total:285  pass:252  dwarn:0   dfail:0   fail:0   skip:33  time:432s
fi-kbl-7500u     total:285  pass:260  dwarn:1   dfail:0   fail:0   skip:24  time:477s
fi-kbl-7567u     total:285  pass:265  dwarn:0   dfail:0   fail:0   skip:20  time:469s
fi-kbl-r         total:285  pass:258  dwarn:0   dfail:0   fail:0   skip:27  time:516s
fi-pnv-d510      total:285  pass:219  dwarn:1   dfail:0   fail:0   skip:65  time:663s
fi-skl-6260u     total:285  pass:265  dwarn:0   dfail:0   fail:0   skip:20  time:439s
fi-skl-6600u     total:285  pass:258  dwarn:0   dfail:0   fail:0   skip:27  time:537s
fi-skl-6700k2    total:285  pass:261  dwarn:0   dfail:0   fail:0   skip:24  time:500s
fi-skl-6770hq    total:285  pass:265  dwarn:0   dfail:0   fail:0   skip:20  time:503s
fi-skl-guc       total:285  pass:256  dwarn:0   dfail:0   fail:1   skip:28  time:427s
fi-skl-gvtdvm    total:285  pass:262  dwarn:0   dfail:0   fail:0   skip:23  time:443s
fi-snb-2520m     total:3    pass:2    dwarn:0   dfail:0   fail:0   skip:0  
Blacklisted hosts:
fi-cnl-psr       total:285  pass:256  dwarn:3   dfail:0   fail:0   skip:26  time:529s
fi-glk-j4005     total:285  pass:256  dwarn:0   dfail:0   fail:0   skip:29  time:488s

23c67dc0cf31917b696b87dac997aca76c0d248d drm-tip: 2018y-03m-28d-06h-36m-40s UTC integration manifest 2eceb2811170 drm: Use srcu to protect drm_device.unplugged

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_8514/issues.html
_______________________________________________
Intel-gfx mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Patchwork

2018-03-28 13:21 UTC #3 lore raw

✓ Fi.CI.IGT: success for drm: Use srcu to protect drm_device.unplugged

In reply to Oleksandr Andrushchenko

== Series Details ==

Series: drm: Use srcu to protect drm_device.unplugged
URL : https://patchwork.freedesktop.org/series/40793/
State : success

== Summary ==

---- Known issues:

Test kms_flip:

        Subgroup 2x-plain-flip-ts-check-interruptible:
                fail       -> PASS       (shard-hsw) fdo#100368 +2
        Subgroup flip-vs-expired-vblank-interruptible:
                pass       -> FAIL       (shard-hsw) fdo#102887 +1
Test kms_plane:
        Subgroup plane-panning-bottom-right-suspend-pipe-b-planes:
                pass       -> FAIL       (shard-apl) fdo#103375
Test kms_setmode:
        Subgroup basic:
                pass       -> FAIL       (shard-hsw) fdo#99912

fdo#100368 https://bugs.freedesktop.org/show_bug.cgi?id=100368
fdo#102887 https://bugs.freedesktop.org/show_bug.cgi?id=102887
fdo#103375 https://bugs.freedesktop.org/show_bug.cgi?id=103375
fdo#99912 https://bugs.freedesktop.org/show_bug.cgi?id=99912

shard-apl        total:3495 pass:1830 dwarn:1   dfail:0   fail:8   skip:1655 time:12974s
shard-hsw        total:3495 pass:1780 dwarn:1   dfail:0   fail:4   skip:1709 time:11632s
shard-snb        total:3495 pass:1373 dwarn:1   dfail:0   fail:4   skip:2117 time:7102s

Blacklisted hosts:
shard-kbl total:3495 pass:1956 dwarn:1 dfail:1 fail:9 skip:1528 time:9683s

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_8514/shards.html
_______________________________________________
Intel-gfx mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Daniel Vetter

Reviewed-by on v1 1/1

2018-03-28 15:09 UTC #4 lore raw

In reply to Oleksandr Andrushchenko

Quoted 7 lines · Oleksandr Andrushchenko

From: Noralf Trønnes <[email protected]>
Use srcu to protect drm_device.unplugged in a race free manner. Drivers can use drm_dev_enter()/drm_dev_exit() to protect and mark sections preventing access to device resources that are not available after the device is gone.

Quoted 6 lines

Suggested-by Daniel Vetter <[email protected]>
Signed-off-by Noralf Trønnes <[email protected]>
Signed-off-by Oleksandr Andrushchenko <[email protected]>
Reviewed-by Oleksandr Andrushchenko <[email protected]>
Tested-by Oleksandr Andrushchenko <[email protected]>
Cc [email protected]

Reviewed-by Daniel Vetter <[email protected]>

Oleksandr, please push to drm-misc-next once you have dim tools setup up and everything.

Thanks, Daniel

Quoted 164 lines

---
 drivers/gpu/drm/drm_drv.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
 include/drm/drm_device.h  |  9 +++++++-
 include/drm/drm_drv.h     | 15 +++++++++----
 3 files changed, 68 insertions(+), 10 deletions(-)

drivers/gpu/drm/drm_drv.c +49 -5

index a1b9338736e3..32a83b41ab61 100644
@@ -32,6 +32,7 @@
 #include <linux/moduleparam.h>
 #include <linux/mount.h>
 #include <linux/slab.h>
+#include <linux/srcu.h>
 
 #include <drm/drm_drv.h>
 #include <drm/drmP.h>

@@ -75,6 +76,8 @@ static bool drm_core_init_complete = false;
 
 static struct dentry *drm_debugfs_root;
 
+DEFINE_STATIC_SRCU(drm_unplug_srcu);
+
 /*
  * DRM Minors
  * A DRM device can provide several char-dev interfaces on the DRM-Major. Each

@@ -318,18 +321,51 @@ void drm_put_dev(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_put_dev);
 
-static void drm_device_set_unplugged(struct drm_device *dev)
+/**
+ * drm_dev_enter - Enter device critical section
+ * @dev: DRM device
+ * @idx: Pointer to index that will be passed to the matching drm_dev_exit()
+ *
+ * This function marks and protects the beginning of a section that should not
+ * be entered after the device has been unplugged. The section end is marked
+ * with drm_dev_exit(). Calls to this function can be nested.
+ *
+ * Returns:
+ * True if it is OK to enter the section, false otherwise.
+ */
+bool drm_dev_enter(struct drm_device *dev, int *idx)
+{
+	*idx = srcu_read_lock(&drm_unplug_srcu);
+
+	if (dev->unplugged) {
+		srcu_read_unlock(&drm_unplug_srcu, *idx);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(drm_dev_enter);
+
+/**
+ * drm_dev_exit - Exit device critical section
+ * @idx: index returned from drm_dev_enter()
+ *
+ * This function marks the end of a section that should not be entered after
+ * the device has been unplugged.
+ */
+void drm_dev_exit(int idx)
 {
-	smp_wmb();
-	atomic_set(&dev->unplugged, 1);
+	srcu_read_unlock(&drm_unplug_srcu, idx);
 }
+EXPORT_SYMBOL(drm_dev_exit);
 
 /**
  * drm_dev_unplug - unplug a DRM device
  * @dev: DRM device
  *
  * This unplugs a hotpluggable DRM device, which makes it inaccessible to
- * userspace operations. Entry-points can use drm_dev_is_unplugged(). This
+ * userspace operations. Entry-points can use drm_dev_enter() and
+ * drm_dev_exit() to protect device resources in a race free manner. This
  * essentially unregisters the device like drm_dev_unregister(), but can be
  * called while there are still open users of @dev.
  */

@@ -338,10 +374,18 @@ void drm_dev_unplug(struct drm_device *dev)
 	drm_dev_unregister(dev);
 
 	mutex_lock(&drm_global_mutex);
-	drm_device_set_unplugged(dev);
 	if (dev->open_count == 0)
 		drm_dev_put(dev);
 	mutex_unlock(&drm_global_mutex);
+
+	/*
+	 * After synchronizing any critical read section is guaranteed to see
+	 * the new value of ->unplugged, and any critical section which might
+	 * still have seen the old value of ->unplugged is guaranteed to have
+	 * finished.
+	 */
+	dev->unplugged = true;
+	synchronize_srcu(&drm_unplug_srcu);
 }
 EXPORT_SYMBOL(drm_dev_unplug);

include/drm/drm_device.h +8 -1

index 7c4fa32f3fc6..3a0eac2885b7 100644
@@ -46,7 +46,14 @@ struct drm_device {
 	/* currently active master for this device. Protected by master_mutex */
 	struct drm_master *master;
 
-	atomic_t unplugged;			/**< Flag whether dev is dead */
+	/**
+	 * @unplugged:
+	 *
+	 * Flag to tell if the device has been unplugged.
+	 * See drm_dev_enter() and drm_dev_is_unplugged().
+	 */
+	bool unplugged;
+
 	struct inode *anon_inode;		/**< inode for private address-space */
 	char *unique;				/**< unique name of the device */
 	/*@} */

include/drm/drm_drv.h +11 -4

index d23dcdd1bd95..7e545f5f94d3 100644
@@ -624,6 +624,8 @@ void drm_dev_get(struct drm_device *dev);
 void drm_dev_put(struct drm_device *dev);
 void drm_dev_unref(struct drm_device *dev);
 void drm_put_dev(struct drm_device *dev);
+bool drm_dev_enter(struct drm_device *dev, int *idx);
+void drm_dev_exit(int idx);
 void drm_dev_unplug(struct drm_device *dev);
 
 /**

@@ -635,11 +637,16 @@ void drm_dev_unplug(struct drm_device *dev);
  * unplugged, these two functions guarantee that any store before calling
  * drm_dev_unplug() is visible to callers of this function after it completes
  */
-static inline int drm_dev_is_unplugged(struct drm_device *dev)
+static inline bool drm_dev_is_unplugged(struct drm_device *dev)
 {
-	int ret = atomic_read(&dev->unplugged);
-	smp_rmb();
-	return ret;
+	int idx;
+
+	if (drm_dev_enter(dev, &idx)) {
+		drm_dev_exit(idx);
+		return false;
+	}
+
+	return true;
 }

Signature · 6 lines

2.7.4

_______________________________________________
dri-devel mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Signature · 7 lines

Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Oleksandr Andrushchenko

author Applied

2018-03-29 11:18 UTC #5 lore raw

Quoted 14 lines · Daniel Vetter

Quoted 7 lines · Oleksandr Andrushchenko
From: Noralf Trønnes <[email protected]>
Use srcu to protect drm_device.unplugged in a race free manner. Drivers can use drm_dev_enter()/drm_dev_exit() to protect and mark sections preventing access to device resources that are not available after the device is gone.
Quoted 6 lines
Suggested-by Daniel Vetter <[email protected]>
Signed-off-by Noralf Trønnes <[email protected]>
Signed-off-by Oleksandr Andrushchenko <[email protected]>
Reviewed-by Oleksandr Andrushchenko <[email protected]>
Tested-by Oleksandr Andrushchenko <[email protected]>
Cc [email protected]

Quoted 4 lines

Reviewed-by Daniel Vetter <[email protected]>
Oleksandr, please push to drm-misc-next once you have dim tools setup up and everything.

Pushed to drm-misc-next

Quoted 2 lines

Thanks, Daniel

Thank you,
Oleksandr

Quoted 157 lines

---
  drivers/gpu/drm/drm_drv.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
  include/drm/drm_device.h  |  9 +++++++-
  include/drm/drm_drv.h     | 15 +++++++++----
  3 files changed, 68 insertions(+), 10 deletions(-)

drivers/gpu/drm/drm_drv.c +49 -5

index a1b9338736e3..32a83b41ab61 100644
@@ -32,6 +32,7 @@
  #include <linux/moduleparam.h>
  #include <linux/mount.h>
  #include <linux/slab.h>
+#include <linux/srcu.h>
 
  #include <drm/drm_drv.h>
  #include <drm/drmP.h>

@@ -75,6 +76,8 @@ static bool drm_core_init_complete = false;
 
  static struct dentry *drm_debugfs_root;
 
+DEFINE_STATIC_SRCU(drm_unplug_srcu);
+
  /*
   * DRM Minors
   * A DRM device can provide several char-dev interfaces on the DRM-Major. Each

@@ -318,18 +321,51 @@ void drm_put_dev(struct drm_device *dev)
  }
  EXPORT_SYMBOL(drm_put_dev);
 
-static void drm_device_set_unplugged(struct drm_device *dev)
+/**
+ * drm_dev_enter - Enter device critical section
+ * @dev: DRM device
+ * @idx: Pointer to index that will be passed to the matching drm_dev_exit()
+ *
+ * This function marks and protects the beginning of a section that should not
+ * be entered after the device has been unplugged. The section end is marked
+ * with drm_dev_exit(). Calls to this function can be nested.
+ *
+ * Returns:
+ * True if it is OK to enter the section, false otherwise.
+ */
+bool drm_dev_enter(struct drm_device *dev, int *idx)
+{
+	*idx = srcu_read_lock(&drm_unplug_srcu);
+
+	if (dev->unplugged) {
+		srcu_read_unlock(&drm_unplug_srcu, *idx);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(drm_dev_enter);
+
+/**
+ * drm_dev_exit - Exit device critical section
+ * @idx: index returned from drm_dev_enter()
+ *
+ * This function marks the end of a section that should not be entered after
+ * the device has been unplugged.
+ */
+void drm_dev_exit(int idx)
  {
-	smp_wmb();
-	atomic_set(&dev->unplugged, 1);
+	srcu_read_unlock(&drm_unplug_srcu, idx);
  }
+EXPORT_SYMBOL(drm_dev_exit);
 
  /**
   * drm_dev_unplug - unplug a DRM device
   * @dev: DRM device
   *
   * This unplugs a hotpluggable DRM device, which makes it inaccessible to
- * userspace operations. Entry-points can use drm_dev_is_unplugged(). This
+ * userspace operations. Entry-points can use drm_dev_enter() and
+ * drm_dev_exit() to protect device resources in a race free manner. This
   * essentially unregisters the device like drm_dev_unregister(), but can be
   * called while there are still open users of @dev.
   */

@@ -338,10 +374,18 @@ void drm_dev_unplug(struct drm_device *dev)
  	drm_dev_unregister(dev);
 
  	mutex_lock(&drm_global_mutex);
-	drm_device_set_unplugged(dev);
  	if (dev->open_count == 0)
  		drm_dev_put(dev);
  	mutex_unlock(&drm_global_mutex);
+
+	/*
+	 * After synchronizing any critical read section is guaranteed to see
+	 * the new value of ->unplugged, and any critical section which might
+	 * still have seen the old value of ->unplugged is guaranteed to have
+	 * finished.
+	 */
+	dev->unplugged = true;
+	synchronize_srcu(&drm_unplug_srcu);
  }
  EXPORT_SYMBOL(drm_dev_unplug);

include/drm/drm_device.h +8 -1

index 7c4fa32f3fc6..3a0eac2885b7 100644
@@ -46,7 +46,14 @@ struct drm_device {
  	/* currently active master for this device. Protected by master_mutex */
  	struct drm_master *master;
 
-	atomic_t unplugged;			/**< Flag whether dev is dead */
+	/**
+	 * @unplugged:
+	 *
+	 * Flag to tell if the device has been unplugged.
+	 * See drm_dev_enter() and drm_dev_is_unplugged().
+	 */
+	bool unplugged;
+
  	struct inode *anon_inode;		/**< inode for private address-space */
  	char *unique;				/**< unique name of the device */
  	/*@} */

include/drm/drm_drv.h +11 -4

index d23dcdd1bd95..7e545f5f94d3 100644
@@ -624,6 +624,8 @@ void drm_dev_get(struct drm_device *dev);
  void drm_dev_put(struct drm_device *dev);
  void drm_dev_unref(struct drm_device *dev);
  void drm_put_dev(struct drm_device *dev);
+bool drm_dev_enter(struct drm_device *dev, int *idx);
+void drm_dev_exit(int idx);
  void drm_dev_unplug(struct drm_device *dev);
 
  /**

@@ -635,11 +637,16 @@ void drm_dev_unplug(struct drm_device *dev);
   * unplugged, these two functions guarantee that any store before calling
   * drm_dev_unplug() is visible to callers of this function after it completes
   */
-static inline int drm_dev_is_unplugged(struct drm_device *dev)
+static inline bool drm_dev_is_unplugged(struct drm_device *dev)
  {
-	int ret = atomic_read(&dev->unplugged);
-	smp_rmb();
-	return ret;
+	int idx;
+
+	if (drm_dev_enter(dev, &idx)) {
+		drm_dev_exit(idx);
+		return false;
+	}
+
+	return true;
  }

Quoted 7 lines

Signature · 6 lines

2.7.4

_______________________________________________
dri-devel mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/dri-devel

_______________________________________________
dri-devel mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/dri-devel