* [PATCH] Btrfs: fix race between enabling quotas and subvolume creation
@ 2018-11-19 16:20 fdmanana
2018-11-20 0:33 ` Qu Wenruo
2018-11-21 16:02 ` David Sterba
0 siblings, 2 replies; 3+ messages in thread
From: fdmanana @ 2018-11-19 16:20 UTC (permalink / raw)
To: linux-btrfs
From: Filipe Manana <fdmanana@suse.com>
We have a race between enabling quotas end subvolume creation that cause
subvolume creation to fail with -EINVAL, and the following diagram shows
how it happens:
CPU 0 CPU 1
btrfs_ioctl()
btrfs_ioctl_quota_ctl()
btrfs_quota_enable()
mutex_lock(fs_info->qgroup_ioctl_lock)
btrfs_ioctl()
create_subvol()
btrfs_qgroup_inherit()
-> save fs_info->quota_root
into quota_root
-> stores a NULL value
-> tries to lock the mutex
qgroup_ioctl_lock
-> blocks waiting for
the task at CPU0
-> sets BTRFS_FS_QUOTA_ENABLED in fs_info
-> sets quota_root in fs_info->quota_root
(non-NULL value)
mutex_unlock(fs_info->qgroup_ioctl_lock)
-> checks quota enabled
flag is set
-> returns -EINVAL because
fs_info->quota_root was
NULL before it acquired
the mutex
qgroup_ioctl_lock
-> ioctl returns -EINVAL
Returning -EINVAL to user space will be confusing if all the arguments
passed to the subvolume creation ioctl were valid.
Fix it by grabbing the value from fs_info->quota_root after acquiring
the mutex.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
fs/btrfs/qgroup.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index ae1358253b7b..0bdf28499790 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2250,7 +2250,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
int i;
u64 *i_qgroups;
struct btrfs_fs_info *fs_info = trans->fs_info;
- struct btrfs_root *quota_root = fs_info->quota_root;
+ struct btrfs_root *quota_root;
struct btrfs_qgroup *srcgroup;
struct btrfs_qgroup *dstgroup;
u32 level_size = 0;
@@ -2260,6 +2260,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
goto out;
+ quota_root = fs_info->quota_root;
if (!quota_root) {
ret = -EINVAL;
goto out;
--
2.11.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] Btrfs: fix race between enabling quotas and subvolume creation
2018-11-19 16:20 [PATCH] Btrfs: fix race between enabling quotas and subvolume creation fdmanana
@ 2018-11-20 0:33 ` Qu Wenruo
2018-11-21 16:02 ` David Sterba
1 sibling, 0 replies; 3+ messages in thread
From: Qu Wenruo @ 2018-11-20 0:33 UTC (permalink / raw)
To: fdmanana, linux-btrfs
[-- Attachment #1.1: Type: text/plain, Size: 3293 bytes --]
On 2018/11/20 上午12:20, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
>
> We have a race between enabling quotas end subvolume creation that cause
> subvolume creation to fail with -EINVAL, and the following diagram shows
> how it happens:
>
> CPU 0 CPU 1
>
> btrfs_ioctl()
> btrfs_ioctl_quota_ctl()
> btrfs_quota_enable()
> mutex_lock(fs_info->qgroup_ioctl_lock)
>
> btrfs_ioctl()
> create_subvol()
> btrfs_qgroup_inherit()
> -> save fs_info->quota_root
> into quota_root
> -> stores a NULL value
> -> tries to lock the mutex
> qgroup_ioctl_lock
> -> blocks waiting for
> the task at CPU0
>
> -> sets BTRFS_FS_QUOTA_ENABLED in fs_info
> -> sets quota_root in fs_info->quota_root
> (non-NULL value)
>
> mutex_unlock(fs_info->qgroup_ioctl_lock)
>
> -> checks quota enabled
> flag is set
> -> returns -EINVAL because
> fs_info->quota_root was
> NULL before it acquired
> the mutex
> qgroup_ioctl_lock
> -> ioctl returns -EINVAL
>
> Returning -EINVAL to user space will be confusing if all the arguments
> passed to the subvolume creation ioctl were valid.
>
> Fix it by grabbing the value from fs_info->quota_root after acquiring
> the mutex.
>
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Thanks,
Qu
> ---
> fs/btrfs/qgroup.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index ae1358253b7b..0bdf28499790 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -2250,7 +2250,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
> int i;
> u64 *i_qgroups;
> struct btrfs_fs_info *fs_info = trans->fs_info;
> - struct btrfs_root *quota_root = fs_info->quota_root;
> + struct btrfs_root *quota_root;
> struct btrfs_qgroup *srcgroup;
> struct btrfs_qgroup *dstgroup;
> u32 level_size = 0;
> @@ -2260,6 +2260,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
> if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
> goto out;
>
> + quota_root = fs_info->quota_root;
> if (!quota_root) {
> ret = -EINVAL;
> goto out;
>
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] Btrfs: fix race between enabling quotas and subvolume creation
2018-11-19 16:20 [PATCH] Btrfs: fix race between enabling quotas and subvolume creation fdmanana
2018-11-20 0:33 ` Qu Wenruo
@ 2018-11-21 16:02 ` David Sterba
1 sibling, 0 replies; 3+ messages in thread
From: David Sterba @ 2018-11-21 16:02 UTC (permalink / raw)
To: fdmanana; +Cc: linux-btrfs
On Mon, Nov 19, 2018 at 04:20:34PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
>
> We have a race between enabling quotas end subvolume creation that cause
> subvolume creation to fail with -EINVAL, and the following diagram shows
> how it happens:
>
> CPU 0 CPU 1
>
> btrfs_ioctl()
> btrfs_ioctl_quota_ctl()
> btrfs_quota_enable()
> mutex_lock(fs_info->qgroup_ioctl_lock)
>
> btrfs_ioctl()
> create_subvol()
> btrfs_qgroup_inherit()
> -> save fs_info->quota_root
> into quota_root
> -> stores a NULL value
> -> tries to lock the mutex
> qgroup_ioctl_lock
> -> blocks waiting for
> the task at CPU0
>
> -> sets BTRFS_FS_QUOTA_ENABLED in fs_info
> -> sets quota_root in fs_info->quota_root
> (non-NULL value)
>
> mutex_unlock(fs_info->qgroup_ioctl_lock)
>
> -> checks quota enabled
> flag is set
> -> returns -EINVAL because
> fs_info->quota_root was
> NULL before it acquired
> the mutex
> qgroup_ioctl_lock
> -> ioctl returns -EINVAL
>
> Returning -EINVAL to user space will be confusing if all the arguments
> passed to the subvolume creation ioctl were valid.
>
> Fix it by grabbing the value from fs_info->quota_root after acquiring
> the mutex.
>
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Added to misc-next, thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2018-11-19 16:20 [PATCH] Btrfs: fix race between enabling quotas and subvolume creation fdmanana
2018-11-20 0:33 ` Qu Wenruo
2018-11-21 16:02 ` David Sterba
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