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Commit 410fb31d authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Greg Kroah-Hartman
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ovl: skip overlayfs superblocks at global sync 



[ Upstream commit 32b1924b210a70dcacdf65abd687c5ef86a67541 ]

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: default avatarDmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Stable-dep-of: b836c4d29f27 ("ima: detect changes to the backing overlay file")
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 04e3ec93

fs/overlayfs/super.c

+3 −2
Original line number Diff line number Diff line
@@ -268,8 +268,8 @@ 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
@@ -1664,6 +1664,7 @@ 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));

fs/sync.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

}

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -1351,6 +1351,8 @@ 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 */