[dm-devel] [PATCH] dm: introduce a no open flag for deferred remove

[Brian Geffon <bgeffon@google.com>]

When a device is being removed with deferred remove it's
still possible to open and use the device. This change
introduces a flag called DM_DEFERRED_REMOVE_NO_OPEN_FLAG
which when used with DM_DEFERRED_REMOVE will cause any
new opens to fail with -ENXIO.

If this flag is used without DM_DEFERRED_REMOVE it will
result in an -EINVAL.

Signed-off-by: Brian Geffon <bgeffon@google.com>
---
 drivers/md/dm-core.h          |  1 +
 drivers/md/dm-ioctl.c         | 39 +++++++++++++++++++++++++++--------
 drivers/md/dm.c               | 21 ++++++++++++++++---
 drivers/md/dm.h               |  9 +++++++-
 include/uapi/linux/dm-ioctl.h | 12 +++++++++--
 5 files changed, 67 insertions(+), 15 deletions(-)

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index b855fef4f38a..b30e59deb4a8 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -139,6 +139,7 @@ struct mapped_device {
 #define DMF_SUSPENDED_INTERNALLY 7
 #define DMF_POST_SUSPENDING 8
 #define DMF_EMULATE_ZONE_APPEND 9
+#define DMF_DEFERRED_REMOVE_NO_OPEN 10
 
 void disable_discard(struct mapped_device *md);
 void disable_write_same(struct mapped_device *md);
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 21fe8652b095..07bb679880de 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -60,7 +60,8 @@ struct vers_iter {
 static struct rb_root name_rb_tree = RB_ROOT;
 static struct rb_root uuid_rb_tree = RB_ROOT;
 
-static void dm_hash_remove_all(bool keep_open_devices, bool mark_deferred, bool only_deferred);
+static void dm_hash_remove_all(bool keep_open_devices, bool mark_deferred,
+		bool deferred_no_open, bool only_deferred);
 
 /*
  * Guards access to both hash tables.
@@ -74,7 +75,7 @@ static DEFINE_MUTEX(dm_hash_cells_mutex);
 
 static void dm_hash_exit(void)
 {
-	dm_hash_remove_all(false, false, false);
+	dm_hash_remove_all(false, false, false, false);
 }
 
 /*-----------------------------------------------------------------
@@ -315,7 +316,8 @@ static struct dm_table *__hash_remove(struct hash_cell *hc)
 	return table;
 }
 
-static void dm_hash_remove_all(bool keep_open_devices, bool mark_deferred, bool only_deferred)
+static void dm_hash_remove_all(bool keep_open_devices, bool mark_deferred,
+		bool deferred_no_open, bool only_deferred)
 {
 	int dev_skipped;
 	struct rb_node *n;
@@ -334,7 +336,8 @@ static void dm_hash_remove_all(bool keep_open_devices, bool mark_deferred, bool
 		dm_get(md);
 
 		if (keep_open_devices &&
-		    dm_lock_for_deletion(md, mark_deferred, only_deferred)) {
+		    dm_lock_for_deletion(md, mark_deferred, deferred_no_open,
+				    only_deferred)) {
 			dm_put(md);
 			dev_skipped++;
 			continue;
@@ -496,7 +499,7 @@ static struct mapped_device *dm_hash_rename(struct dm_ioctl *param,
 
 void dm_deferred_remove(void)
 {
-	dm_hash_remove_all(true, false, true);
+	dm_hash_remove_all(true, false, false, true);
 }
 
 /*-----------------------------------------------------------------
@@ -510,7 +513,13 @@ typedef int (*ioctl_fn)(struct file *filp, struct dm_ioctl *param, size_t param_
 
 static int remove_all(struct file *filp, struct dm_ioctl *param, size_t param_size)
 {
-	dm_hash_remove_all(true, !!(param->flags & DM_DEFERRED_REMOVE), false);
+	if (param->flags & DM_DEFERRED_REMOVE_NO_OPEN_FLAG &&
+			!(param->flags & DM_DEFERRED_REMOVE)) {
+		return -EINVAL;
+	}
+
+	dm_hash_remove_all(true, !!(param->flags & DM_DEFERRED_REMOVE),
+			!!(param->flags & DM_DEFERRED_REMOVE_NO_OPEN_FLAG), false);
 	param->data_size = 0;
 	return 0;
 }
@@ -811,9 +820,13 @@ static void __dev_status(struct mapped_device *md, struct dm_ioctl *param)
 	if (dm_suspended_internally_md(md))
 		param->flags |= DM_INTERNAL_SUSPEND_FLAG;
 
-	if (dm_test_deferred_remove_flag(md))
+	if (dm_test_deferred_remove_flag(md)) {
 		param->flags |= DM_DEFERRED_REMOVE;
 
+		if (dm_test_deferred_remove_no_open_flag(md))
+			param->flags |= DM_DEFERRED_REMOVE_NO_OPEN_FLAG;
+	}
+
 	param->dev = huge_encode_dev(disk_devt(disk));
 
 	/*
@@ -960,10 +973,18 @@ static int dev_remove(struct file *filp, struct dm_ioctl *param, size_t param_si
 
 	md = hc->md;
 
+	if (param->flags & DM_DEFERRED_REMOVE_NO_OPEN_FLAG &&
+			!(param->flags & DM_DEFERRED_REMOVE)) {
+		up_write(&_hash_lock);
+		dm_put(md);
+		return -EINVAL;
+	}
+
 	/*
 	 * Ensure the device is not open and nothing further can open it.
 	 */
-	r = dm_lock_for_deletion(md, !!(param->flags & DM_DEFERRED_REMOVE), false);
+	r = dm_lock_for_deletion(md, !!(param->flags & DM_DEFERRED_REMOVE),
+			!!(param->flags & DM_DEFERRED_REMOVE_NO_OPEN_FLAG), false);
 	if (r) {
 		if (r == -EBUSY && param->flags & DM_DEFERRED_REMOVE) {
 			up_write(&_hash_lock);
@@ -984,7 +1005,7 @@ static int dev_remove(struct file *filp, struct dm_ioctl *param, size_t param_si
 		dm_table_destroy(t);
 	}
 
-	param->flags &= ~DM_DEFERRED_REMOVE;
+	param->flags &= ~(DM_DEFERRED_REMOVE | DM_DEFERRED_REMOVE_NO_OPEN_FLAG);
 
 	dm_ima_measure_on_device_remove(md, false);
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c0ae8087c602..90b74043e162 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -315,7 +315,10 @@ static int dm_blk_open(struct block_device *bdev, fmode_t mode)
 		goto out;
 
 	if (test_bit(DMF_FREEING, &md->flags) ||
+	    test_bit(DMF_DEFERRED_REMOVE_NO_OPEN, &md->flags) ||
 	    dm_deleting_md(md)) {
+		BUG_ON(test_bit(DMF_DEFERRED_REMOVE_NO_OPEN, &md->flags) &&
+		       !test_bit(DMF_DEFERRED_REMOVE, &md->flags));
 		md = NULL;
 		goto out;
 	}
@@ -355,7 +358,8 @@ int dm_open_count(struct mapped_device *md)
 /*
  * Guarantees nothing is using the device before it's deleted.
  */
-int dm_lock_for_deletion(struct mapped_device *md, bool mark_deferred, bool only_deferred)
+int dm_lock_for_deletion(struct mapped_device *md, bool mark_deferred,
+		bool deferred_no_open, bool only_deferred)
 {
 	int r = 0;
 
@@ -363,8 +367,12 @@ int dm_lock_for_deletion(struct mapped_device *md, bool mark_deferred, bool only
 
 	if (dm_open_count(md)) {
 		r = -EBUSY;
-		if (mark_deferred)
+		if (mark_deferred) {
 			set_bit(DMF_DEFERRED_REMOVE, &md->flags);
+
+			if (deferred_no_open)
+				set_bit(DMF_DEFERRED_REMOVE_NO_OPEN, &md->flags);
+		}
 	} else if (only_deferred && !test_bit(DMF_DEFERRED_REMOVE, &md->flags))
 		r = -EEXIST;
 	else
@@ -383,8 +391,10 @@ int dm_cancel_deferred_remove(struct mapped_device *md)
 
 	if (test_bit(DMF_DELETING, &md->flags))
 		r = -EBUSY;
-	else
+	else {
 		clear_bit(DMF_DEFERRED_REMOVE, &md->flags);
+		clear_bit(DMF_DEFERRED_REMOVE_NO_OPEN, &md->flags);
+	}
 
 	spin_unlock(&_minor_lock);
 
@@ -2718,6 +2728,11 @@ int dm_test_deferred_remove_flag(struct mapped_device *md)
 	return test_bit(DMF_DEFERRED_REMOVE, &md->flags);
 }
 
+int dm_test_deferred_remove_no_open_flag(struct mapped_device *md)
+{
+	return test_bit(DMF_DEFERRED_REMOVE_NO_OPEN, &md->flags);
+}
+
 int dm_suspended(struct dm_target *ti)
 {
 	return dm_suspended_md(ti->table->md);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 9013dc1a7b00..8d0d4344f882 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -158,6 +158,12 @@ void dm_internal_resume(struct mapped_device *md);
  */
 int dm_test_deferred_remove_flag(struct mapped_device *md);
 
+/*
+ * Test if the device is scheduled for deferred remove while
+ * disallowing opens.
+ */
+int dm_test_deferred_remove_no_open_flag(struct mapped_device *md);
+
 /*
  * Try to remove devices marked for deferred removal.
  */
@@ -198,7 +204,8 @@ void dm_stripe_exit(void);
 void dm_destroy(struct mapped_device *md);
 void dm_destroy_immediate(struct mapped_device *md);
 int dm_open_count(struct mapped_device *md);
-int dm_lock_for_deletion(struct mapped_device *md, bool mark_deferred, bool only_deferred);
+int dm_lock_for_deletion(struct mapped_device *md, bool mark_deferred,
+			 bool deferred_no_open, bool only_deferred);
 int dm_cancel_deferred_remove(struct mapped_device *md);
 int dm_request_based(struct mapped_device *md);
 int dm_get_table_device(struct mapped_device *md, dev_t dev, fmode_t mode,
diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index c12ce30b52df..c0fee607b827 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -286,9 +286,9 @@ enum {
 #define DM_DEV_SET_GEOMETRY	_IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR	4
-#define DM_VERSION_MINOR	45
+#define DM_VERSION_MINOR	46
 #define DM_VERSION_PATCHLEVEL	0
-#define DM_VERSION_EXTRA	"-ioctl (2021-03-22)"
+#define DM_VERSION_EXTRA	"-ioctl (2022-01-21)"
 
 /* Status bits */
 #define DM_READONLY_FLAG	(1 << 0) /* In/Out */
@@ -382,4 +382,12 @@ enum {
  */
 #define DM_IMA_MEASUREMENT_FLAG	(1 << 19) /* In */
 
+/* If set with DF_DEFERRED_REMOVE if an immediate remove is not
+ * possible because the device is still open any new additional
+ * opens will also be rejected.
+ *
+ * It is an error to specify this flag without DM_DEFERRED_REMOVE.
+ */
+#define DM_DEFERRED_REMOVE_NO_OPEN_FLAG	(1 << 20) /* In/Out */
+
 #endif				/* _LINUX_DM_IOCTL_H */
-- 
2.35.0.rc0.227.g00780c9af4-goog

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