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

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Message-ID: <76ca65df-8ffb-97b8-50ca-29f22ecf7c34@nod.at>
Date:   Wed, 17 May 2017 00:27:44 +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 17.05.2017 um 00:07 schrieb Eric Biggers:
>>> 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?
>
> Both; the inode "leak" isn't filesystem-specific, beyond the fact that UBIFS
> apparently limits the number of inodes on its orphan list while ext4 does not.
> (How do I know it happens on ext4 then?  /proc/slabinfo shows that lots of ext4
> inodes have been allocated, and after an unclean shutdown and remounting, it's
> reported that 50,000+ orphan inodes were deleted.)

UBIFS's orphan list is limited by the size of a LEB (logical erase block).
With nandsim's default settings such a LEB is rather small and can store only
2k orphans.

> There are lots of cases in which path lookups switch from rcu-walk mode into
> ref-walk mode, so the fact that it was being caused by ->d_revalidate() in this
> specific situation isn't really important, IMO.
> 
> I think the actual fix would be something along the lines of making vfs_rmdir()
> unhash any negative child dentries, so that they get "killed" by dput() later.

Thanks,
//richard