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ovl: skip overlayfs superblocks at global sync

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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>
This commit is contained in:
Konstantin Khlebnikov
2020-04-09 11:29:47 +03:00
committed by Miklos Szeredi
parent 62a8a85be8
commit 32b1924b21
3 changed files with 7 additions and 3 deletions
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5
fs/overlayfs/super.c
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@@ -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);