linux-kernel - [PATCH 5.0 092/238] Btrfs: setup a nofs context for memory allocation at __btrfs_set

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Message-Id: <20190322111304.006504743@linuxfoundation.org>
Date:   Fri, 22 Mar 2019 12:15:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nikolay Borisov <nborisov@...e.com>,
        Filipe Manana <fdmanana@...e.com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 5.0 092/238] Btrfs: setup a nofs context for memory allocation at __btrfs_set_acl

5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Filipe Manana <fdmanana@...e.com>

commit a0873490660246db587849a9e172f2b7b21fa88a upstream.

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")
CC: stable@...r.kernel.org # 4.9+
Reviewed-by: Nikolay Borisov <nborisov@...e.com>
Signed-off-by: Filipe Manana <fdmanana@...e.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/acl.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- 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_
 	}
 
 	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;