From 8c85e455f7c9682d2728e64aaaf36b8c490dfce3 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 9 Apr 2020 11:29:47 +0300 Subject: 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: Dmitry Monakhov Signed-off-by: Konstantin Khlebnikov Reviewed-by: Amir Goldstein Signed-off-by: Miklos Szeredi Stable-dep-of: b836c4d29f27 ("ima: detect changes to the backing overlay file") Signed-off-by: Sasha Levin --- fs/overlayfs/super.c | 5 +++-- fs/sync.c | 3 ++- include/linux/fs.h | 2 ++ 3 files changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index f5cf0938f298..fcf453f7f4ae 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -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)); diff --git a/fs/sync.c b/fs/sync.c index 4d1ff010bc5a..16c2630ee4bf 100644 --- a/fs/sync.c +++ b/fs/sync.c @@ -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); } diff --git a/include/linux/fs.h b/include/linux/fs.h index 4b1553f570f2..fbbd7ef7f653 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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 */ -- cgit v1.2.3