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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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3
fs/sync.c
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@ -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);
}