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ovl: skip overlayfs superblocks at global sync 

[ Upstream commit 32b1924b21 ]

Stacked filesystems like overlayfs has no own writeback, but they have to
forward syncfs() requests to backend for keeping data integrity.

During global sync() each overlayfs instance calls method ->sync_fs() for
backend although it itself is in global list of superblocks too.  As a
result one syscall sync() could write one superblock several times and send
multiple disk barriers.

This patch adds flag SB_I_SKIP_SYNC into sb->sb_iflags to avoid that.

Reported-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Stable-dep-of: b836c4d29f ("ima: detect changes to the backing overlay file")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Konstantin Khlebnikov 2020-04-09 11:29:47 +03:00 committed by Greg Kroah-Hartman
parent 157c8056ab
commit 8c85e455f7
3 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
fs/overlayfs/super.c
View File

@ -263,8 +263,8 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
return 0;
/*
* If this is a sync(2) call or an emergency sync, all the super blocks
* will be iterated, including upper_sb, so no need to do anything.
* Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
* All the super blocks will be iterated, including upper_sb.
*
* If this is a syncfs(2) call, then we do need to call
* sync_filesystem() on upper_sb, but enough if we do it when being
@ -1710,6 +1710,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
sb->s_xattr = ovl_xattr_handlers;
sb->s_fs_info = ofs;
sb->s_flags |= SB_POSIXACL;
sb->s_iflags |= SB_I_SKIP_SYNC;
err = -ENOMEM;
root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));

3
fs/sync.c
View File

@ -76,7 +76,8 @@ static void sync_inodes_one_sb(struct super_block *sb, void *arg)
static void sync_fs_one_sb(struct super_block *sb, void *arg)
{
if (!sb_rdonly(sb) && sb->s_op->sync_fs)
if (!sb_rdonly(sb) && !(sb->s_iflags & SB_I_SKIP_SYNC) &&
sb->s_op->sync_fs)
sb->s_op->sync_fs(sb, *(int *)arg);
}

2
include/linux/fs.h
View File

@ -1404,6 +1404,8 @@ extern int send_sigurg(struct fown_struct *fown);
#define SB_I_IMA_UNVERIFIABLE_SIGNATURE 0x00000020
#define SB_I_UNTRUSTED_MOUNTER 0x00000040
#define SB_I_SKIP_SYNC 0x00000100 /* Skip superblock at global sync */
/* Possible states of 'frozen' field */
enum {
SB_UNFROZEN = 0, /* FS is unfrozen */