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authorVivek Goyal <vgoyal@redhat.com>2018-05-11 11:49:28 -0400
committerMiklos Szeredi <mszeredi@redhat.com>2018-07-20 09:56:08 +0200
commit0c2888749363645d62cc48852d0af98d5ceef332 (patch)
treed2e8932551adc3a41cb164223a0e9db6c8d2a1c0 /fs/overlayfs/super.c
parent2002df85367ca69961d39020f56d3d727897be01 (diff)
downloadlinux-0c2888749363645d62cc48852d0af98d5ceef332.tar.bz2
ovl: A new xattr OVL_XATTR_METACOPY for file on upper
Now we will have the capability to have upper inodes which might be only metadata copy up and data is still on lower inode. So add a new xattr OVL_XATTR_METACOPY to distinguish between two cases. Presence of OVL_XATTR_METACOPY reflects that file has been copied up metadata only and and data will be copied up later from lower origin. So this xattr is set when a metadata copy takes place and cleared when data copy takes place. We also use a bit in ovl_inode->flags to cache OVL_UPPERDATA which reflects whether ovl inode has data or not (as opposed to metadata only copy up). If a file is copied up metadata only and later when same file is opened for WRITE, then data copy up takes place. We copy up data, remove METACOPY xattr and then set the UPPERDATA flag in ovl_inode->flags. While all these operations happen with oi->lock held, read side of oi->flags can be lockless. That is another thread on another cpu can check if UPPERDATA flag is set or not. So this gives us an ordering requirement w.r.t UPPERDATA flag. That is, if another cpu sees UPPERDATA flag set, then it should be guaranteed that effects of data copy up and remove xattr operations are also visible. For example. CPU1 CPU2 ovl_open() acquire(oi->lock) ovl_open_maybe_copy_up() ovl_copy_up_data() open_open_need_copy_up() vfs_removexattr() ovl_already_copied_up() ovl_dentry_needs_data_copy_up() ovl_set_flag(OVL_UPPERDATA) ovl_test_flag(OVL_UPPERDATA) release(oi->lock) Say CPU2 is copying up data and in the end sets UPPERDATA flag. But if CPU1 perceives the effects of setting UPPERDATA flag but not the effects of preceding operations (ex. upper that is not fully copied up), it will be a problem. Hence this patch introduces smp_wmb() on setting UPPERDATA flag operation and smp_rmb() on UPPERDATA flag test operation. May be some other lock or barrier is already covering it. But I am not sure what that is and is it obvious enough that we will not break it in future. So hence trying to be safe here and introducing barriers explicitly for UPPERDATA flag/bit. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Reviewed-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs/super.c')
-rw-r--r--fs/overlayfs/super.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index d4caeee051ee..ab0039161f85 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1485,6 +1485,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
/* Root is always merge -> can have whiteouts */
ovl_set_flag(OVL_WHITEOUTS, d_inode(root_dentry));
ovl_dentry_set_flag(OVL_E_CONNECTED, root_dentry);
+ ovl_set_upperdata(d_inode(root_dentry));
ovl_inode_init(d_inode(root_dentry), upperpath.dentry,
ovl_dentry_lower(root_dentry));