4.19-stable review patch. If anyone has any objections, please let me know.
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From: Konstantin Khlebnikov khlebnikov@yandex-team.ru
[ 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 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 Stable-dep-of: b836c4d29f27 ("ima: detect changes to the backing overlay file") Signed-off-by: Sasha Levin sashal@kernel.org --- 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 1a7a1e2988855..1c1eb873e6ecc 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -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)); diff --git a/fs/sync.c b/fs/sync.c index b54e0541ad899..917ebd12c2515 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 95b8ef09b76cf..f89748aac8c32 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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 */