linux-kernel - Re: dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry

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Message-ID: <20180313003647.GS30522@ZenIV.linux.org.uk>
Date:   Tue, 13 Mar 2018 00:36:47 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: dcache: remove trylock loops (was Re: [BUG] lock_parent()
 breakage when used from shrink_dentry_list())

On Mon, Mar 12, 2018 at 06:28:30PM -0500, Eric W. Biederman wrote:

> Given that nfs_kill_super calls generic_shutdown_super and
> generic_shutdown_super calls shrink_dcache_for_umount
> I would argue that nfsv2 and nfsv3 are buggy in the same
> case, as shrink_dcache_for_umount is called on something
> that is not the root of the filesystem's dentry tree.

That's not a problem - it will simply evict a subtree first,
then go through ->s_roots and kill each piece.