On 19.07.2018 17:49, Josef Bacik wrote:
> If we're allocating a new space cache inode it's likely going to be
> under a transaction handle, so we need to use GFP_NOFS to keep from
> deadlocking. Otherwise GFP_KERNEL is fine.
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/free-space-cache.c | 5 +++++
> fs/btrfs/inode.c | 3 ++-
> fs/btrfs/transaction.h | 1 +
> 3 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index d5f80cb300be..13bc514e4e16 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -68,7 +68,12 @@ static struct inode *__lookup_free_space_inode(struct btrfs_root *root,
> btrfs_disk_key_to_cpu(&location, &disk_key);
> btrfs_release_path(path);
>
> + /* We need this set so that we use GFP_NOFS when allocating our inode. */
> + if (current->journal_info == NULL)
> + current->journal_info = BTRFS_TRANS_STUB;
> inode = btrfs_iget(fs_info->sb, &location, root, NULL);
> + if (current->journal_info == BTRFS_TRANS_STUB)
> + current->journal_info = NULL;
This is not safe in the face of stacked filesystem, i.e ext4 uses the
journal_info.
> if (IS_ERR(inode))
> return inode;
> if (is_bad_inode(inode)) {
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index eba61bcb9bb3..14ecfe5d6110 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -9211,8 +9211,9 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
> struct btrfs_fs_info *fs_info = btrfs_sb(sb);
> struct btrfs_inode *ei;
> struct inode *inode;
> + gfp_t flags = (current->journal_info) ? GFP_NOFS : GFP_KERNEL;
>
> - ei = kmem_cache_alloc(btrfs_inode_cachep, GFP_KERNEL);
> + ei = kmem_cache_alloc(btrfs_inode_cachep, flags);
Why don't you just hardcode GFP_NOFS? We should be striving at removing
abuse of ->journal_info than proliferating it.
> if (!ei)
> return NULL;
>
> diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
> index 94439482a0ec..172ff923bf15 100644
> --- a/fs/btrfs/transaction.h
> +++ b/fs/btrfs/transaction.h
> @@ -106,6 +106,7 @@ struct btrfs_transaction {
> #define TRANS_EXTWRITERS (__TRANS_START | __TRANS_ATTACH)
>
> #define BTRFS_SEND_TRANS_STUB ((void *)1)
> +#define BTRFS_TRANS_STUB ((void *)2)
>
> struct btrfs_trans_handle {
> u64 transid;
>
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