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Date:   Wed, 25 Mar 2020 02:13:27 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Qian Cai <cai@lca.pw>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Null-ptr-deref due to "sanitized pathwalk machinery (v4)"
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On Tue, Mar 24, 2020 at 09:49:48PM -0400, Qian Cai wrote:

> It does not catch anything at all with the patch,

You mean, oops happens, but neither WARN_ON() is triggered?
Lovely...  Just to make sure: could you slap the same couple
of lines just before
                if (unlikely(!d_can_lookup(nd->path.dentry))) {
in link_path_walk(), just to check if I have misread the trace
you've got?

Does that (+ other two inserts) end up with
	1) some of these WARN_ON() triggered when oops happens or
	2) oops is happening, but neither WARN_ON() triggers or
	3) oops not happening / becoming harder to hit?