Re: [PATCH] Btrfs: use nofs context when initializing security xattrs to avoid deadlock

[Nikolay Borisov <nborisov@suse.com>]

On 10.12.18 г. 19:53 ч., fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> When initializing the security xattrs, we are holding a transaction handle
> therefore we need to use a GFP_NOFS context in order to avoid a deadlock
> with reclaim in case it's triggered.
> 
> Fixes: 39a27ec1004e8 ("btrfs: use GFP_KERNEL for xattr and acl allocations")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/xattr.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> index ea78c3d6dcfc..f141b45ce349 100644
> --- a/fs/btrfs/xattr.c
> +++ b/fs/btrfs/xattr.c
> @@ -11,6 +11,7 @@
>  #include <linux/security.h>
>  #include <linux/posix_acl_xattr.h>
>  #include <linux/iversion.h>
> +#include <linux/sched/mm.h>
>  #include "ctree.h"
>  #include "btrfs_inode.h"
>  #include "transaction.h"
> @@ -422,9 +423,15 @@ static int btrfs_initxattrs(struct inode *inode,
>  {
>  	const struct xattr *xattr;
>  	struct btrfs_trans_handle *trans = fs_info;
> +	unsigned int nofs_flag;
>  	char *name;
>  	int err = 0;
>  
> +	/*
> +	 * We're holding a transaction handle, so use a NOFS memory allocation
> +	 * context to avoid deadlock if reclaim happens.
> +	 */
> +	nofs_flag = memalloc_nofs_save();
>  	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
>  		name = kmalloc(XATTR_SECURITY_PREFIX_LEN +
>  			       strlen(xattr->name) + 1, GFP_KERNEL);
> @@ -440,6 +447,7 @@ static int btrfs_initxattrs(struct inode *inode,
>  		if (err < 0)
>  			break;
>  	}
> +	memalloc_nofs_restore(nofs_flag);
>  	return err;
>  }
>  
>