linux-kernel - Re: bug in migrate page

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Message-Id: <20070822115258.7d59aaa1.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 22 Aug 2007 11:52:58 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, clameter@....com
Subject: Re: bug in migrate page

On Wed, 22 Aug 2007 10:08:09 +0800
Shaohua Li <shaohua.li@...el.com> wrote:

> commit dc386d4d1e98bb39fb967ee156cd456c802fc692 adds rcu_read_lock, but
> some routines in the lock range might sleep (like lock_buffer,
> aops->writepage), I saw a 'sleep in atomic' warning. It appears the
> patch has several versions before. Doing rcu_read_lock in PageAnon
> sounds break the case of PageAnon(page) && PageSwapCache(page),
> as .writepage might be called. The dummy anon patch maybe is ok.
> 

Thank you for catching.

Maybe you're correct.

BTW, in PageAnon(page) && PageSwapCache(page) case, I can't find when
.writepage is called. Could you explain ?

In my understanding,

rcu_read_lock()
	-> try_to_unmap()
	-> move_to_new_page()
		-> migrate_page() // swap has .migratepage member.
			-> migrate_page_move_mapping().
			-> migrate_page_copy().
		-> remove_migration_ptes().


At quick glance, above path has no writepage() ops.
just replace swap's radix tree entry.

Thanks,
-Kame

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