From b71759ef1e1730db81dab98e9dab9455e8c7f5a2 Mon Sep 17 00:00:00 2001 From: Chengguang Xu Date: Sat, 24 Apr 2021 22:03:15 +0800 Subject: ovl: skip checking lower file's i_writecount on truncate It is possible that a directory tree is shared between multiple overlay instances as a lower layer. In this case when one instance executes a file residing on the lower layer, the other instance denies a truncate(2) call on this file. This only happens for truncate(2) and not for open(2) with the O_TRUNC flag. Fix this interference and inconsistency by removing the preliminary i_writecount check before copy-up. This means that unlike on normal filesystems truncate(argv[0]) will now succeed. If this ever causes a regression in a real world use case this needs to be revisited. One way to fix this properly would be to keep a correct i_writecount in the overlay inode, but that is difficult due to memory mapping code only dealing with the real file/inode. Signed-off-by: Chengguang Xu Signed-off-by: Miklos Szeredi --- fs/overlayfs/inode.c | 6 ------ 1 file changed, 6 deletions(-) (limited to 'fs/overlayfs') diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 37300e972a39..8aa370e8143a 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -33,12 +33,6 @@ int ovl_setattr(struct user_namespace *mnt_userns, struct dentry *dentry, goto out; if (attr->ia_valid & ATTR_SIZE) { - struct inode *realinode = d_inode(ovl_dentry_real(dentry)); - - err = -ETXTBSY; - if (atomic_read(&realinode->i_writecount) < 0) - goto out_drop_write; - /* Truncate should trigger data copy up as well */ full_copy_up = true; } -- cgit v1.2.3