diff mbox series

[v2,3/7] btrfs: handle allocation failure in strdup

Message ID 20191113102728.8835-4-jthumshirn@suse.de (mailing list archive)
State New, archived
Headers show
Series [v2,1/7] btrfs: decrement number of open devices after closing the device not before | expand

Commit Message

Johannes Thumshirn Nov. 13, 2019, 10:27 a.m. UTC 
Gracefully handle allocation failures in btrfs_close_one_device()'s
rcu_string_strdup() instead of crashing the machine.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 fs/btrfs/volumes.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

Comments

Anand Jain Nov. 14, 2019, 11 a.m. UTC | #1 
On 13/11/19 6:27 PM, Johannes Thumshirn wrote:
> Gracefully handle allocation failures in btrfs_close_one_device()'s
> rcu_string_strdup() instead of crashing the machine.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
>   fs/btrfs/volumes.c | 22 ++++++++++++++--------
>   1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 0a2a73907563..e5864ca3bb3b 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1064,7 +1064,7 @@ static void btrfs_close_bdev(struct btrfs_device *device)
>   static int btrfs_close_one_device(struct btrfs_device *device)
>   {
>   	struct btrfs_fs_devices *fs_devices = device->fs_devices;
> -	struct btrfs_device *new_device;
> +	struct btrfs_device *new_device = NULL;
>   	struct rcu_string *name;
>   
>   	new_device = btrfs_alloc_device(NULL, &device->devid,
> @@ -1072,6 +1072,15 @@ static int btrfs_close_one_device(struct btrfs_device *device)
>   	if (IS_ERR(new_device))
>   		goto err_close_device;
>   
> +	/* Safe because we are under uuid_mutex */
> +	if (device->name) {
> +		name = rcu_string_strdup(device->name->str, GFP_NOFS);
> +		if (!name)
> +			goto err_free_device;
> +
> +		rcu_assign_pointer(new_device->name, name);
> +	}
> +


  Any idea why do we need to strdup() at all to close a device?

Thanks, Anand


>   	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
>   	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
>   		list_del_init(&device->dev_alloc_list);
> @@ -1085,13 +1094,6 @@ static int btrfs_close_one_device(struct btrfs_device *device)
>   	if (device->bdev)
>   		fs_devices->open_devices--;
>   
> -	/* Safe because we are under uuid_mutex */
> -	if (device->name) {
> -		name = rcu_string_strdup(device->name->str, GFP_NOFS);
> -		BUG_ON(!name); /* -ENOMEM */
> -		rcu_assign_pointer(new_device->name, name);
> -	}
> -
>   	list_replace_rcu(&device->dev_list, &new_device->dev_list);
>   	new_device->fs_devices = device->fs_devices;
>   
> @@ -1100,6 +1102,10 @@ static int btrfs_close_one_device(struct btrfs_device *device)
>   
>   	return 0;
>   
> +err_free_device:
> +	if (new_device)
> +		btrfs_free_device(new_device);
> +
>   err_close_device:
>   	btrfs_close_bdev(device);
>   	if (device->bdev) {
>
David Sterba Nov. 15, 2019, 9:39 a.m. UTC | #2 
On Thu, Nov 14, 2019 at 07:00:54PM +0800, Anand Jain wrote:
> On 13/11/19 6:27 PM, Johannes Thumshirn wrote:
> > Gracefully handle allocation failures in btrfs_close_one_device()'s
> > rcu_string_strdup() instead of crashing the machine.
> > 
> > Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> > ---
> >   fs/btrfs/volumes.c | 22 ++++++++++++++--------
> >   1 file changed, 14 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index 0a2a73907563..e5864ca3bb3b 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -1064,7 +1064,7 @@ static void btrfs_close_bdev(struct btrfs_device *device)
> >   static int btrfs_close_one_device(struct btrfs_device *device)
> >   {
> >   	struct btrfs_fs_devices *fs_devices = device->fs_devices;
> > -	struct btrfs_device *new_device;
> > +	struct btrfs_device *new_device = NULL;
> >   	struct rcu_string *name;
> >   
> >   	new_device = btrfs_alloc_device(NULL, &device->devid,
> > @@ -1072,6 +1072,15 @@ static int btrfs_close_one_device(struct btrfs_device *device)
> >   	if (IS_ERR(new_device))
> >   		goto err_close_device;
> >   
> > +	/* Safe because we are under uuid_mutex */
> > +	if (device->name) {
> > +		name = rcu_string_strdup(device->name->str, GFP_NOFS);
> > +		if (!name)
> > +			goto err_free_device;
> > +
> > +		rcu_assign_pointer(new_device->name, name);
> > +	}
> > +
> 
>   Any idea why do we need to strdup() at all to close a device?

It shouldn't be needed but that's how it got implemented since the
beginning in e4404d6e8da678d852. The device on close is duplicated, so
has to be the name.
Nikolay Borisov Nov. 15, 2019, 9:11 p.m. UTC | #3 
On 13.11.19 г. 12:27 ч., Johannes Thumshirn wrote:
> Gracefully handle allocation failures in btrfs_close_one_device()'s
> rcu_string_strdup() instead of crashing the machine.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
>  fs/btrfs/volumes.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 0a2a73907563..e5864ca3bb3b 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1064,7 +1064,7 @@ static void btrfs_close_bdev(struct btrfs_device *device)
>  static int btrfs_close_one_device(struct btrfs_device *device)
>  {
>  	struct btrfs_fs_devices *fs_devices = device->fs_devices;
> -	struct btrfs_device *new_device;
> +	struct btrfs_device *new_device = NULL;
>  	struct rcu_string *name;
>  
>  	new_device = btrfs_alloc_device(NULL, &device->devid,
> @@ -1072,6 +1072,15 @@ static int btrfs_close_one_device(struct btrfs_device *device)
>  	if (IS_ERR(new_device))
>  		goto err_close_device;
>  
> +	/* Safe because we are under uuid_mutex */
> +	if (device->name) {
> +		name = rcu_string_strdup(device->name->str, GFP_NOFS);
> +		if (!name)
> +			goto err_free_device;
> +
> +		rcu_assign_pointer(new_device->name, name);
> +	}

This could really be:


diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e148b13905c5..7bb3cd8afa7a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1086,11 +1086,8 @@ static void btrfs_close_one_device(struct
btrfs_device *device)
        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(!name); /* -ENOMEM */
-               rcu_assign_pointer(new_device->name, name);
-       }
+       new_device->name = device->name;
+       device->name = NULL;

        list_replace_rcu(&device->dev_list, &new_device->dev_list);
        new_device->fs_devices = device->fs_devices;

rcu_string_free already checks if device->name is non-NULL.


<snip>
diff mbox series

Patch

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 0a2a73907563..e5864ca3bb3b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1064,7 +1064,7 @@  static void btrfs_close_bdev(struct btrfs_device *device)
 static int btrfs_close_one_device(struct btrfs_device *device)
 {
 	struct btrfs_fs_devices *fs_devices = device->fs_devices;
-	struct btrfs_device *new_device;
+	struct btrfs_device *new_device = NULL;
 	struct rcu_string *name;
 
 	new_device = btrfs_alloc_device(NULL, &device->devid,
@@ -1072,6 +1072,15 @@  static int btrfs_close_one_device(struct btrfs_device *device)
 	if (IS_ERR(new_device))
 		goto err_close_device;
 
+	/* Safe because we are under uuid_mutex */
+	if (device->name) {
+		name = rcu_string_strdup(device->name->str, GFP_NOFS);
+		if (!name)
+			goto err_free_device;
+
+		rcu_assign_pointer(new_device->name, name);
+	}
+
 	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
 	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
 		list_del_init(&device->dev_alloc_list);
@@ -1085,13 +1094,6 @@  static int btrfs_close_one_device(struct btrfs_device *device)
 	if (device->bdev)
 		fs_devices->open_devices--;
 
-	/* Safe because we are under uuid_mutex */
-	if (device->name) {
-		name = rcu_string_strdup(device->name->str, GFP_NOFS);
-		BUG_ON(!name); /* -ENOMEM */
-		rcu_assign_pointer(new_device->name, name);
-	}
-
 	list_replace_rcu(&device->dev_list, &new_device->dev_list);
 	new_device->fs_devices = device->fs_devices;
 
@@ -1100,6 +1102,10 @@  static int btrfs_close_one_device(struct btrfs_device *device)
 
 	return 0;
 
+err_free_device:
+	if (new_device)
+		btrfs_free_device(new_device);
+
 err_close_device:
 	btrfs_close_bdev(device);
 	if (device->bdev) {