linux-kernel - Re: d_lookup: Unable to handle kernel paging request

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Date:   Sat, 25 May 2019 00:21:11 +0200
From:   Vicente Bergas <vicencb@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: d_lookup: Unable to handle kernel paging request

On Wednesday, May 22, 2019 6:29:46 PM CEST, Al Viro wrote:
> On Wed, May 22, 2019 at 05:44:30PM +0200, Vicente Bergas wrote:
> ...
> IOW, here we have also run into bogus hlist forward pointer or head -
> same 0x1000000 in one case and 0x0000880001000000 in two others.
>
> Have you tried to see if KASAN catches anything on those loads?
> Use-after-free, for example...  Another thing to try: slap
> 	WARN_ON(entry->d_flags & DCACHE_NORCU);
> in __d_rehash() and see if it triggers.

Hi,
i have been running 3 days with KASAN enabled and also with
diff a/fs/dcache.c b/fs/dcache.c
@@ -2395,3 +2395,4 @@ static void __d_rehash(struct dentry *entry)
 	struct hlist_bl_head *b = d_hash(entry->d_name.hash);
 
+	WARN_ON(entry->d_flags & DCACHE_NORCU);
 	hlist_bl_lock(b);
but the issue has not appeared again.
Next week i will try -rc2 without KASAN and with WARN_ON and see if it
triggers.

Regards,
  Vicenç.