From 32b1924b210a70dcacdf65abd687c5ef86a67541 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 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 --- fs/overlayfs/super.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'fs/overlayfs') diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 6e3fa96613f5..f57aa348dcd6 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -261,8 +261,8 @@ 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 @@ -1870,6 +1870,7 @@ 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 = ovl_get_root(sb, upperpath.dentry, oe); -- cgit v1.2.3