[PATCH] Btrfs: setup a nofs context for memory allocation at __btrfs_set_acl

[PATCH] Btrfs: setup a nofs context for memory allocation at __btrfs_set_acl

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

We are holding a transaction handle when setting an acl, therefore we can
not allocate the xattr value buffer using GFP_KERNEL, as we could deadlock
if reclaim is triggered by the allocation, therefore setup a nofs context.

Fixes: 39a27ec1004e8 ("btrfs: use GFP_KERNEL for xattr and acl allocations")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/acl.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
index 3b66c957ea6f..5810463dc6d2 100644
--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -9,6 +9,7 @@
 #include <linux/posix_acl_xattr.h>
 #include <linux/posix_acl.h>
 #include <linux/sched.h>
+#include <linux/sched/mm.h>
 #include <linux/slab.h>
 
 #include "ctree.h"
@@ -72,8 +73,16 @@ static int __btrfs_set_acl(struct btrfs_trans_handle *trans,
 	}
 
 	if (acl) {
+		unsigned int nofs_flag;
+
 		size = posix_acl_xattr_size(acl->a_count);
+		/*
+		 * We're holding a transaction handle, so use a NOFS memory
+		 * allocation context to avoid deadlock if reclaim happens.
+		 */
+		nofs_flag = memalloc_nofs_save();
 		value = kmalloc(size, GFP_KERNEL);
+		memalloc_nofs_restore(nofs_flag);
 		if (!value) {
 			ret = -ENOMEM;
 			goto out;
-- 
2.11.0

Re: [PATCH] Btrfs: setup a nofs context for memory allocation at __btrfs_set_acl

[Nikolay Borisov]

On 13.12.18 г. 23:16 ч., fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> We are holding a transaction handle when setting an acl, therefore we can
> not allocate the xattr value buffer using GFP_KERNEL, as we could deadlock
> if reclaim is triggered by the allocation, therefore setup a nofs context.
> 
> 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/acl.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
> index 3b66c957ea6f..5810463dc6d2 100644
> --- a/fs/btrfs/acl.c
> +++ b/fs/btrfs/acl.c
> @@ -9,6 +9,7 @@
>  #include <linux/posix_acl_xattr.h>
>  #include <linux/posix_acl.h>
>  #include <linux/sched.h>
> +#include <linux/sched/mm.h>
>  #include <linux/slab.h>
>  
>  #include "ctree.h"
> @@ -72,8 +73,16 @@ static int __btrfs_set_acl(struct btrfs_trans_handle *trans,
>  	}
>  
>  	if (acl) {
> +		unsigned int nofs_flag;
> +
>  		size = posix_acl_xattr_size(acl->a_count);
> +		/*
> +		 * We're holding a transaction handle, so use a NOFS memory
> +		 * allocation context to avoid deadlock if reclaim happens.
> +		 */
> +		nofs_flag = memalloc_nofs_save();
>  		value = kmalloc(size, GFP_KERNEL);
> +		memalloc_nofs_restore(nofs_flag);
>  		if (!value) {
>  			ret = -ENOMEM;
>  			goto out;
> 

Re: [PATCH] Btrfs: setup a nofs context for memory allocation at __btrfs_set_acl

[David Sterba]

On Thu, Dec 13, 2018 at 09:16:56PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> We are holding a transaction handle when setting an acl, therefore we can
> not allocate the xattr value buffer using GFP_KERNEL, as we could deadlock
> if reclaim is triggered by the allocation, therefore setup a nofs context.
> 
> Fixes: 39a27ec1004e8 ("btrfs: use GFP_KERNEL for xattr and acl allocations")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next, thanks.