linux-kernel - Re: Question on fscrypt_d_revalidate() and fstest generic/429

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Date:   Tue, 16 May 2017 08:47:43 +0200
From:   Richard Weinberger <richard@....at>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     linux-fscrypt@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Eric Biggers <ebiggers@...gle.com>,
        Theodore Ts'o <tytso@....edu>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Gstir <david@...ma-star.at>,
        David Oberhollenzer <david.oberhollenzer@...ma-star.at>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        Artem Bityutskiy <dedekind1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: Question on fscrypt_d_revalidate() and fstest generic/429

Eric,

Am 16.05.2017 um 01:25 schrieb Eric Biggers:
> On Mon, May 15, 2017 at 09:51:03PM +0200, Richard Weinberger wrote:
>>>
>>> The test is repeatedly creating and removing a directory "dir" while lookups are
>>> being done in it.  It seems the problem is that many dentries are being created
>>> for "dir", and they pin many different inodes, all at the same time.  This
>>> actually happens for ext4 too; it just doesn't cause an observable error.
>>>
>>> I doubt it's the right solution to make fscrypt_d_revalidate() look at
>>> ->i_nlink, since ->d_revalidate() is meant to validate the filename, not the
>>> inode.  I think there is probably a VFS bug that is causing the dentries to not
>>> be freed.
>>
>> Not sure. Al? :-)
>>
> 
> I can reproduce this on an unencrypted directory after updating path_init() in
> fs/namei.c to always clear LOOKUP_RCU, so that all path lookups are done in
> ref-walk mode.  So I think fscrypt_d_revalidate() was only relevant because it
> causes all path lookups to drop out of rcu-walk mode.

On ext4 or UBIFS?

Thanks,
//richard