linux-kernel - Re: [PATCH] mm: documentation: remove hopelessly out-of-date locking doc

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Message-ID: <52AAC1FE.1010409@suse.cz>
Date:	Fri, 13 Dec 2013 09:14:54 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Dave Hansen <dave.hansen@...el.com>, akpm@...ux-foundation.org
CC:	hughd@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: documentation: remove hopelessly out-of-date locking
 doc

On 12/10/2013 08:18 PM, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@...el.com>
>
> Documentation/vm/locking is a blast from the past.  In the entire
> git history, it has had precisely Three modifications.  Two of
> those look to be pure renames, and the third was from 2005.
>
> The doc contains such gems as:
>
>> The page_table_lock is grabbed while holding the
>> kernel_lock spinning monitor.
>
>> Page stealers hold kernel_lock to protect against a bunch of
>> races.
>
> Or this which talks about mmap_sem:
>
>> 4. The exception to this rule is expand_stack, which just
>>     takes the read lock and the page_table_lock, this is ok
>>     because it doesn't really modify fields anybody relies on.
>
> expand_stack() doesn't take any locks any more directly, and the
> mmap_sem acquisition was long ago moved up in to the page fault
> code itself.
>
> It could be argued that we need to rewrite this, but it is
> dangerous to leave it as-is.  It will confuse more people than it
> helps.

Heh yeah, when I started few months ago and stumbled upon this doc, 
people in the office suggested that I could send a patch that just 
deletes it. I wasn't that brave, but I agree nevertheless.

> Signed-off-by: Dave Hansen <dave.hansen@...el.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

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