Re: [PATCH 01/33] vfs: syscall: Add open_tree(2) to reference or clone a mount [ver #11]
From: Al Viro <viro@ZenIV.linux.org.uk>
Date: 2018-08-02 21:29:23
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On Thu, Aug 02, 2018 at 06:31:06PM +0100, Alan Jenkins wrote:
Hi I found this interesting, though I don't entirely follow the kernel mount/unmount code. I had one puzzle about the code, and two questions which I was largely able to answer. On 01/08/18 16:24, David Howells wrote:quoted
+void dissolve_on_fput(struct vfsmount *mnt) +{ + namespace_lock(); + lock_mount_hash(); + mntget(mnt); + umount_tree(real_mount(mnt), UMOUNT_SYNC); + unlock_mount_hash(); + namespace_unlock(); +}Can I ask why UMOUNT_SYNC is used here? I feel like I must have missed something, but doesn't it skip the IS_MNT_LOCKED() check in disconnect_mount() ? UMOUNT_SYNC seems used for non-lazy unmounts, and in internal cleanups where userspace wouldn't be able to see. But I think userspace can keep watching in this case, e.g. by `fd2 = openat(fd, ".", O_PATH)` (or `fd2 = open_tree(fd, ".", 0)` ?). I would think this function should avoid using UMOUNT_SYNC, like lazy unmount avoids it.
FWIW, I suspect that UMOUNT_CONNECTED might be the right thing here...