linux-kernel - Re: How to explain to lock validator: locking inodes in inode order

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Message-Id: <1153193513.4533.3.camel@testmachine>
Date:	Tue, 18 Jul 2006 05:31:53 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Joshua Hudson <joshudson@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: How to explain to lock validator: locking inodes in inode order

On Mon, 2006-07-17 at 19:24 -0700, Joshua Hudson wrote:
> Code does this:
> 
> /* Lock two items. See locking.txt */
> static inline void kb0_lock2m(struct kb0_idata *m1, struct kb0_idata *m2)
> {
>         if (m1->vi.i_ino > m2->vi.i_ino)
>                 mutex_lock(&m2->k_mutex);
>         mutex_lock(&m1->k_mutex);
>         if (m1->vi.i_ino < m2->vi.i_ino)
>                 mutex_lock(&m2->k_mutex);
> }
> 
> Not sure how to explain to the lock validator that this code can never deadlock.

you're sure it can;t? (which fs is this btw?)

all places in the kernel that take this mutex in that order only do it
in i_ino order, including all directory operations like cross directory
rename?

(if so you can explain normal parent/child nesting, but only if so)

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