On Sun, Feb 10, 2019 at 04:24:22AM +0000, Al Viro wrote:
> In "net/unix/af_unix.c: Set ATIME on socket inode" (back in
> 2002) we'd grown something rather odd in unix_find_other(). In the
> original patch it was
> u=unix_find_socket_byname(sunname, len, type, hash);
> - if (!u)
> + if (u) {
> + struct dentry *dentry;
> + dentry = u->protinfo.af_unix.dentry;
> + if (dentry)
> + UPDATE_ATIME(dentry->d_inode);
> + } else
> goto fail;
It's this commit:
https://github.com/dmgerman/linux-bitkeeper/commit/80cbc5b9c7393c4456236543ca1e639ea0841c19
There are two hunks in that patch: one after "if (sunname->sun_path[0])"
and the other after "else". I just did some more digging and found the
private discussion of the time, as well as a previous revision of the
patch (against 2.2.21, whereas the committed one was against 2.4.x of
the same era). Even the earliest revision I found already has both
hunks. I couldn't find any discussion as to why the second hunk was
possibly needed. It is quite possible that I had added it in error.
The original problem this patch addressed was stmpclean deleting sockets
that were still actively used - specifically, PostgreSQL's. I found
that I also tested the patch on /dev/log and X11 sockets. However, I
can't find any indication of me ever testing with the first hunk only,
so it's quite possible I wrote both hunks at once and only tested both.
> These days the code is
>
> u = unix_find_socket_byname(net, sunname, len, type, hash);
> if (u) {
> struct dentry *dentry;
> dentry = unix_sk(u)->path.dentry;
> if (dentry)
> touch_atime(&unix_sk(u)->path);
> } else
> goto fail;
>
> but the logics is the same. It's the abstract address case - we have
> '\0' in sunname->sun_path[0]. How in hell could that possibly have
> non-NULL ->path.dentry and what would it be?
This is probably in fact impossible.
I think it'd make sense to drop this logic, reverting to:
if (!u)
goto fail;
and then see if atime on an actively used socket in /tmp or on /dev/log
keeps getting updated (due to the first hunk of the above commit).
Alexander
