[PATCH 0/4] btrfs_device fixes

[PATCH 0/4] btrfs_device fixes

[Ilya Dryomov]

Hello,

This patch series does two things:

- adds allocation helpers for struct btrfs_device and struct
  btrfs_fs_devices so that all the list_heads, spinlocks, etc are
  properly initialized and the code for that is in one place;

- fixes a bug in the umount sequence, which, under certain conditions,
  can lead to mount failures.

This is on top of 3.11-rc3, but applies cleanly to btrfs-next/master as
of now.  You can pull from:

git://github.com/idryomov/btrfs-unstable.git dev-fixes
 
Thanks,

		Ilya


Ilya Dryomov (4):
  Btrfs: find_next_devid: root -> fs_info
  Btrfs: add btrfs_alloc_device and switch to it
  Btrfs: add alloc_fs_devices and switch to it
  Btrfs: rollback btrfs_device fields on umount

 fs/btrfs/volumes.c |  250 +++++++++++++++++++++++++++++++++-------------------
 fs/btrfs/volumes.h |    3 +
 2 files changed, 162 insertions(+), 91 deletions(-)

-- 
1.7.10.4

[PATCH 1/4] Btrfs: find_next_devid: root -> fs_info

[Ilya Dryomov]

find_next_devid() knows which root to search, so it should take an
fs_info instead of an arbitrary root.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 fs/btrfs/volumes.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 78b8717..ae1bcb0 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1307,15 +1307,14 @@ static u64 find_next_chunk(struct btrfs_fs_info *fs_info)
 	return ret;
 }
 
-static noinline int find_next_devid(struct btrfs_root *root, u64 *objectid)
+static noinline int find_next_devid(struct btrfs_fs_info *fs_info,
+				    u64 *devid_ret)
 {
 	int ret;
 	struct btrfs_key key;
 	struct btrfs_key found_key;
 	struct btrfs_path *path;
 
-	root = root->fs_info->chunk_root;
-
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
@@ -1324,20 +1323,21 @@ static noinline int find_next_devid(struct btrfs_root *root, u64 *objectid)
 	key.type = BTRFS_DEV_ITEM_KEY;
 	key.offset = (u64)-1;
 
-	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	ret = btrfs_search_slot(NULL, fs_info->chunk_root, &key, path, 0, 0);
 	if (ret < 0)
 		goto error;
 
 	BUG_ON(ret == 0); /* Corruption */
 
-	ret = btrfs_previous_item(root, path, BTRFS_DEV_ITEMS_OBJECTID,
+	ret = btrfs_previous_item(fs_info->chunk_root, path,
+				  BTRFS_DEV_ITEMS_OBJECTID,
 				  BTRFS_DEV_ITEM_KEY);
 	if (ret) {
-		*objectid = 1;
+		*devid_ret = 1;
 	} else {
 		btrfs_item_key_to_cpu(path->nodes[0], &found_key,
 				      path->slots[0]);
-		*objectid = found_key.offset + 1;
+		*devid_ret = found_key.offset + 1;
 	}
 	ret = 0;
 error:
@@ -1971,7 +1971,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
 	}
 	rcu_assign_pointer(device->name, name);
 
-	ret = find_next_devid(root, &device->devid);
+	ret = find_next_devid(root->fs_info, &device->devid);
 	if (ret) {
 		rcu_string_free(device->name);
 		kfree(device);
-- 
1.7.10.4

[PATCH 2/4] Btrfs: add btrfs_alloc_device and switch to it

[Ilya Dryomov]

Currently btrfs_device is allocated ad-hoc in a few different places,
and as a result not all fields are initialized properly.  In particular,
readahead state is only initialized in device_list_add (at scan time),
and not in btrfs_init_new_device (when the new device is added with
'btrfs dev add').  Fix this by adding an allocation helper and switch
everybody but __btrfs_close_devices to it.  (__btrfs_close_devices is
dealt with in a later commit.)

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 fs/btrfs/volumes.c |  150 ++++++++++++++++++++++++++++++++--------------------
 fs/btrfs/volumes.h |    3 ++
 2 files changed, 96 insertions(+), 57 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index ae1bcb0..fe52704 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -101,6 +101,27 @@ void btrfs_cleanup_fs_uuids(void)
 	}
 }
 
+static struct btrfs_device *__alloc_device(void)
+{
+	struct btrfs_device *dev;
+
+	dev = kzalloc(sizeof(*dev), GFP_NOFS);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&dev->dev_list);
+	INIT_LIST_HEAD(&dev->dev_alloc_list);
+
+	spin_lock_init(&dev->io_lock);
+
+	spin_lock_init(&dev->reada_lock);
+	atomic_set(&dev->reada_in_flight, 0);
+	INIT_RADIX_TREE(&dev->reada_zones, GFP_NOFS & ~__GFP_WAIT);
+	INIT_RADIX_TREE(&dev->reada_extents, GFP_NOFS & ~__GFP_WAIT);
+
+	return dev;
+}
+
 static noinline struct btrfs_device *__find_device(struct list_head *head,
 						   u64 devid, u8 *uuid)
 {
@@ -414,17 +435,12 @@ static noinline int device_list_add(const char *path,
 		if (fs_devices->opened)
 			return -EBUSY;
 
-		device = kzalloc(sizeof(*device), GFP_NOFS);
-		if (!device) {
+		device = btrfs_alloc_device(NULL, &devid,
+					    disk_super->dev_item.uuid);
+		if (IS_ERR(device)) {
 			/* we can safely leave the fs_devices entry around */
-			return -ENOMEM;
+			return PTR_ERR(device);
 		}
-		device->devid = devid;
-		device->dev_stats_valid = 0;
-		device->work.func = pending_bios_fn;
-		memcpy(device->uuid, disk_super->dev_item.uuid,
-		       BTRFS_UUID_SIZE);
-		spin_lock_init(&device->io_lock);
 
 		name = rcu_string_strdup(path, GFP_NOFS);
 		if (!name) {
@@ -432,15 +448,6 @@ static noinline int device_list_add(const char *path,
 			return -ENOMEM;
 		}
 		rcu_assign_pointer(device->name, name);
-		INIT_LIST_HEAD(&device->dev_alloc_list);
-
-		/* init readahead state */
-		spin_lock_init(&device->reada_lock);
-		device->reada_curr_zone = NULL;
-		atomic_set(&device->reada_in_flight, 0);
-		device->reada_next = 0;
-		INIT_RADIX_TREE(&device->reada_zones, GFP_NOFS & ~__GFP_WAIT);
-		INIT_RADIX_TREE(&device->reada_extents, GFP_NOFS & ~__GFP_WAIT);
 
 		mutex_lock(&fs_devices->device_list_mutex);
 		list_add_rcu(&device->dev_list, &fs_devices->devices);
@@ -491,8 +498,9 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
 	list_for_each_entry(orig_dev, &orig->devices, dev_list) {
 		struct rcu_string *name;
 
-		device = kzalloc(sizeof(*device), GFP_NOFS);
-		if (!device)
+		device = btrfs_alloc_device(NULL, &orig_dev->devid,
+					    orig_dev->uuid);
+		if (IS_ERR(device))
 			goto error;
 
 		/*
@@ -506,13 +514,6 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
 		}
 		rcu_assign_pointer(device->name, name);
 
-		device->devid = orig_dev->devid;
-		device->work.func = pending_bios_fn;
-		memcpy(device->uuid, orig_dev->uuid, sizeof(device->uuid));
-		spin_lock_init(&device->io_lock);
-		INIT_LIST_HEAD(&device->dev_list);
-		INIT_LIST_HEAD(&device->dev_alloc_list);
-
 		list_add(&device->dev_list, &fs_devices->devices);
 		device->fs_devices = fs_devices;
 		fs_devices->num_devices++;
@@ -1956,10 +1957,10 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
 	}
 	mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
 
-	device = kzalloc(sizeof(*device), GFP_NOFS);
-	if (!device) {
+	device = btrfs_alloc_device(root->fs_info, NULL, NULL);
+	if (IS_ERR(device)) {
 		/* we can safely leave the fs_devices entry around */
-		ret = -ENOMEM;
+		ret = PTR_ERR(device);
 		goto error;
 	}
 
@@ -1971,13 +1972,6 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
 	}
 	rcu_assign_pointer(device->name, name);
 
-	ret = find_next_devid(root->fs_info, &device->devid);
-	if (ret) {
-		rcu_string_free(device->name);
-		kfree(device);
-		goto error;
-	}
-
 	trans = btrfs_start_transaction(root, 0);
 	if (IS_ERR(trans)) {
 		rcu_string_free(device->name);
@@ -1992,9 +1986,6 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
 	if (blk_queue_discard(q))
 		device->can_discard = 1;
 	device->writeable = 1;
-	device->work.func = pending_bios_fn;
-	generate_random_uuid(device->uuid);
-	spin_lock_init(&device->io_lock);
 	device->generation = trans->transid;
 	device->io_width = root->sectorsize;
 	device->io_align = root->sectorsize;
@@ -2142,9 +2133,9 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_root *root, char *device_path,
 		}
 	}
 
-	device = kzalloc(sizeof(*device), GFP_NOFS);
-	if (!device) {
-		ret = -ENOMEM;
+	device = btrfs_alloc_device(NULL, BTRFS_DEV_REPLACE_DEVID, NULL);
+	if (IS_ERR(device)) {
+		ret = PTR_ERR(device);
 		goto error;
 	}
 
@@ -2161,10 +2152,6 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_root *root, char *device_path,
 		device->can_discard = 1;
 	mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
 	device->writeable = 1;
-	device->work.func = pending_bios_fn;
-	generate_random_uuid(device->uuid);
-	device->devid = BTRFS_DEV_REPLACE_DEVID;
-	spin_lock_init(&device->io_lock);
 	device->generation = 0;
 	device->io_width = root->sectorsize;
 	device->io_align = root->sectorsize;
@@ -5314,23 +5301,72 @@ static struct btrfs_device *add_missing_dev(struct btrfs_root *root,
 	struct btrfs_device *device;
 	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
 
-	device = kzalloc(sizeof(*device), GFP_NOFS);
-	if (!device)
+	device = btrfs_alloc_device(NULL, &devid, dev_uuid);
+	if (IS_ERR(device))
 		return NULL;
-	list_add(&device->dev_list,
-		 &fs_devices->devices);
-	device->devid = devid;
-	device->work.func = pending_bios_fn;
+
+	list_add(&device->dev_list, &fs_devices->devices);
 	device->fs_devices = fs_devices;
-	device->missing = 1;
 	fs_devices->num_devices++;
+
+	device->missing = 1;
 	fs_devices->missing_devices++;
-	spin_lock_init(&device->io_lock);
-	INIT_LIST_HEAD(&device->dev_alloc_list);
-	memcpy(device->uuid, dev_uuid, BTRFS_UUID_SIZE);
+
 	return device;
 }
 
+/**
+ * btrfs_alloc_device - allocate struct btrfs_device
+ * @fs_info:	used only for generating a new devid, can be NULL if
+ *		devid is provided (i.e. @devid != NULL).
+ * @devid:	a pointer to devid for this device.  If NULL a new devid
+ *		is generated.
+ * @uuid:	a pointer to UUID for this device.  If NULL a new UUID
+ *		is generated.
+ *
+ * Return: a pointer to a new &struct btrfs_device on success; ERR_PTR()
+ * on error.  Returned struct is not linked onto any lists and can be
+ * destroyed with kfree() right away.
+ */
+struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
+					const u64 *devid,
+					const u8 *uuid)
+{
+	struct btrfs_device *dev;
+	u64 tmp;
+
+	if (!devid && !fs_info) {
+		WARN_ON(1);
+		return ERR_PTR(-EINVAL);
+	}
+
+	dev = __alloc_device();
+	if (IS_ERR(dev))
+		return dev;
+
+	if (devid)
+		tmp = *devid;
+	else {
+		int ret;
+
+		ret = find_next_devid(fs_info, &tmp);
+		if (ret) {
+			kfree(dev);
+			return ERR_PTR(ret);
+		}
+	}
+	dev->devid = tmp;
+
+	if (uuid)
+		memcpy(dev->uuid, uuid, BTRFS_UUID_SIZE);
+	else
+		generate_random_uuid(dev->uuid);
+
+	dev->work.func = pending_bios_fn;
+
+	return dev;
+}
+
 static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
 			  struct extent_buffer *leaf,
 			  struct btrfs_chunk *chunk)
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 8670558..5706cd8 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -298,6 +298,9 @@ void btrfs_close_extra_devices(struct btrfs_fs_info *fs_info,
 int btrfs_find_device_missing_or_by_path(struct btrfs_root *root,
 					 char *device_path,
 					 struct btrfs_device **device);
+struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
+					const u64 *devid,
+					const u8 *uuid);
 int btrfs_rm_device(struct btrfs_root *root, char *device_path);
 void btrfs_cleanup_fs_uuids(void);
 int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len);
-- 
1.7.10.4

[PATCH 3/4] Btrfs: add alloc_fs_devices and switch to it

[Ilya Dryomov]

In the spirit of btrfs_alloc_device, add a helper for allocating and
doing some common initialization of btrfs_fs_devices struct.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 fs/btrfs/volumes.c |   71 +++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 53 insertions(+), 18 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index fe52704..af17b17 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -62,6 +62,48 @@ static void unlock_chunks(struct btrfs_root *root)
 	mutex_unlock(&root->fs_info->chunk_mutex);
 }
 
+static struct btrfs_fs_devices *__alloc_fs_devices(void)
+{
+	struct btrfs_fs_devices *fs_devs;
+
+	fs_devs = kzalloc(sizeof(*fs_devs), GFP_NOFS);
+	if (!fs_devs)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_init(&fs_devs->device_list_mutex);
+
+	INIT_LIST_HEAD(&fs_devs->devices);
+	INIT_LIST_HEAD(&fs_devs->alloc_list);
+	INIT_LIST_HEAD(&fs_devs->list);
+
+	return fs_devs;
+}
+
+/**
+ * alloc_fs_devices - allocate struct btrfs_fs_devices
+ * @fsid:	a pointer to UUID for this FS.  If NULL a new UUID is
+ *		generated.
+ *
+ * Return: a pointer to a new &struct btrfs_fs_devices on success;
+ * ERR_PTR() on error.  Returned struct is not linked onto any lists and
+ * can be destroyed with kfree() right away.
+ */
+static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid)
+{
+	struct btrfs_fs_devices *fs_devs;
+
+	fs_devs = __alloc_fs_devices();
+	if (IS_ERR(fs_devs))
+		return fs_devs;
+
+	if (fsid)
+		memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);
+	else
+		generate_random_uuid(fs_devs->fsid);
+
+	return fs_devs;
+}
+
 static void free_fs_devices(struct btrfs_fs_devices *fs_devices)
 {
 	struct btrfs_device *device;
@@ -416,16 +458,14 @@ static noinline int device_list_add(const char *path,
 
 	fs_devices = find_fsid(disk_super->fsid);
 	if (!fs_devices) {
-		fs_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
-		if (!fs_devices)
-			return -ENOMEM;
-		INIT_LIST_HEAD(&fs_devices->devices);
-		INIT_LIST_HEAD(&fs_devices->alloc_list);
+		fs_devices = alloc_fs_devices(disk_super->fsid);
+		if (IS_ERR(fs_devices))
+			return PTR_ERR(fs_devices);
+
 		list_add(&fs_devices->list, &fs_uuids);
-		memcpy(fs_devices->fsid, disk_super->fsid, BTRFS_FSID_SIZE);
 		fs_devices->latest_devid = devid;
 		fs_devices->latest_trans = found_transid;
-		mutex_init(&fs_devices->device_list_mutex);
+
 		device = NULL;
 	} else {
 		device = __find_device(&fs_devices->devices, devid,
@@ -481,18 +521,13 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
 	struct btrfs_device *device;
 	struct btrfs_device *orig_dev;
 
-	fs_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
-	if (!fs_devices)
-		return ERR_PTR(-ENOMEM);
+	fs_devices = alloc_fs_devices(orig->fsid);
+	if (IS_ERR(fs_devices))
+		return fs_devices;
 
-	INIT_LIST_HEAD(&fs_devices->devices);
-	INIT_LIST_HEAD(&fs_devices->alloc_list);
-	INIT_LIST_HEAD(&fs_devices->list);
-	mutex_init(&fs_devices->device_list_mutex);
 	fs_devices->latest_devid = orig->latest_devid;
 	fs_devices->latest_trans = orig->latest_trans;
 	fs_devices->total_devices = orig->total_devices;
-	memcpy(fs_devices->fsid, orig->fsid, sizeof(fs_devices->fsid));
 
 	/* We have held the volume lock, it is safe to get the devices. */
 	list_for_each_entry(orig_dev, &orig->devices, dev_list) {
@@ -1794,9 +1829,9 @@ static int btrfs_prepare_sprout(struct btrfs_root *root)
 	if (!fs_devices->seeding)
 		return -EINVAL;
 
-	seed_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
-	if (!seed_devices)
-		return -ENOMEM;
+	seed_devices = __alloc_fs_devices();
+	if (IS_ERR(seed_devices))
+		return PTR_ERR(seed_devices);
 
 	old_devices = clone_fs_devices(fs_devices);
 	if (IS_ERR(old_devices)) {
-- 
1.7.10.4

[PATCH 4/4] Btrfs: rollback btrfs_device fields on umount

[Ilya Dryomov]

It turns out we don't properly rollback in-core btrfs_device state on
umount.  We zero out ->bdev, ->in_fs_metadata and that's about it.  In
particular, we don't zero out ->generation, and this can lead to us
refusing a mount -- a non-NULL fs_devices->latest_bdev is essential, but
btrfs_close_extra_devices will happily assign NULL to ->latest_bdev if
the first device on the dev_list happens to be missing and consequently
has no bdev attached.  This happens because since commit a6b0d5c8
btrfs_close_extra_devices adjusts ->latest_bdev, and in doing that,
relies on the ->generation.  Fix this, and possibly other problems, by
zeroing out everything except for what device_list_add sets, so that a
mount right after insmod and 'btrfs dev scan' is no different from any
later mount in this respect.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 fs/btrfs/volumes.c |   15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index af17b17..2f6bc12 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -673,22 +673,19 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 		if (device->can_discard)
 			fs_devices->num_can_discard--;
 
-		new_device = kmalloc(sizeof(*new_device), GFP_NOFS);
-		BUG_ON(!new_device); /* -ENOMEM */
-		memcpy(new_device, device, sizeof(*new_device));
+		new_device = btrfs_alloc_device(NULL, &device->devid,
+						device->uuid);
+		BUG_ON(IS_ERR(new_device)); /* -ENOMEM */
 
 		/* Safe because we are under uuid_mutex */
 		if (device->name) {
 			name = rcu_string_strdup(device->name->str, GFP_NOFS);
-			BUG_ON(device->name && !name); /* -ENOMEM */
+			BUG_ON(!name); /* -ENOMEM */
 			rcu_assign_pointer(new_device->name, name);
 		}
-		new_device->bdev = NULL;
-		new_device->writeable = 0;
-		new_device->in_fs_metadata = 0;
-		new_device->can_discard = 0;
-		spin_lock_init(&new_device->io_lock);
+
 		list_replace_rcu(&device->dev_list, &new_device->dev_list);
+		new_device->fs_devices = device->fs_devices;
 
 		call_rcu(&device->rcu, free_device);
 	}
-- 
1.7.10.4

Re: [PATCH 2/4] Btrfs: add btrfs_alloc_device and switch to it

[Stefan Behrens]

On Mon, 12 Aug 2013 14:33:02 +0300, Ilya Dryomov wrote:
> Currently btrfs_device is allocated ad-hoc in a few different places,
> and as a result not all fields are initialized properly.  In particular,
> readahead state is only initialized in device_list_add (at scan time),
> and not in btrfs_init_new_device (when the new device is added with
> 'btrfs dev add').  Fix this by adding an allocation helper and switch
> everybody but __btrfs_close_devices to it.  (__btrfs_close_devices is
> dealt with in a later commit.)
> 
> Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
> ---
>  fs/btrfs/volumes.c |  150 ++++++++++++++++++++++++++++++++--------------------
>  fs/btrfs/volumes.h |    3 ++
>  2 files changed, 96 insertions(+), 57 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index ae1bcb0..fe52704 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
[...]


> @@ -2142,9 +2133,9 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_root *root, char *device_path,
>  		}
>  	}
>  
> -	device = kzalloc(sizeof(*device), GFP_NOFS);
> -	if (!device) {
> -		ret = -ENOMEM;
> +	device = btrfs_alloc_device(NULL, BTRFS_DEV_REPLACE_DEVID, NULL);
> +	if (IS_ERR(device)) {
> +		ret = PTR_ERR(device);

BTRFS_DEV_REPLACE_DEVID is not a "const u64 *devid".


> +struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
> +					const u64 *devid,
> +					const u8 *uuid)
> +{
> +	struct btrfs_device *dev;
> +	u64 tmp;
> +
> +	if (!devid && !fs_info) {
> +		WARN_ON(1);
> +		return ERR_PTR(-EINVAL);
> +	}

This WARN_ON(1) is triggered with the device replace procedure because
BTRFS_DEV_REPLACE_DEVID is zero.

Re: [PATCH 2/4] Btrfs: add btrfs_alloc_device and switch to it

[Ilya Dryomov]

On Fri, Aug 23, 2013 at 10:35 AM, Stefan Behrens
<sbehrens@giantdisaster.de> wrote:
> This WARN_ON(1) is triggered with the device replace procedure because
> BTRFS_DEV_REPLACE_DEVID is zero.

Ah, a dreaded 0 in C.  What a screw up.  This came from my rebuild
branch where btrfs_init_dev_replace_tgtdev is a bit different, and I
just auto-merged it.  I'll fix it up.

Thanks,

                Ilya