linux-kernel - Re: DNAME_INLINE_LEN versus CONFIG_GENERIC

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Date:	Thu, 03 Jul 2014 12:53:01 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Nick Piggin <npiggin@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: DNAME_INLINE_LEN versus CONFIG_GENERIC_LOCKBREAK

Rasmus Villemoes <linux@...musvillemoes.dk> writes:

> In dcache.h, DNAME_INLINE_LEN is carefully chosen so that sizeof(struct
> dentry) is a (specific) multiple of 64 bytes. Obviously this breaks when
> certain debug options are chosen (DEBUG_LOCK_ALLOC and DEBUG_SPINLOCK),
> but also, AFAICT, on architectures with CONFIG_GENERIC_LOCKBREAK.
>
> I'm not sure it matters, but if it does, I'd suggest putting a
> BUILD_BUG_ON somewhere, protected by suitable #ifdefs, so that the code
> documents the assumptions that went into the particular choice of
> DNAME_INLINE_LEN (this would also help catch changes to some of the
> structures embedded in struct dentry which would violate those
> assumptions). 

The right fix would be to pad it correctly for these other variants
too.

Checking for magic numbers would be nasty though.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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