linux-kernel - Re: [PATCH][RESEND for 2.6.29-rc8-mm1] skip I

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Date:	Wed, 1 Apr 2009 08:53:09 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"stable@...nel.org" <stable@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jack@...e.cz" <jack@...e.cz>,
	"m.mizuma@...fujitsu.com" <m.mizuma@...fujitsu.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"npiggin@...e.de" <npiggin@...e.de>
Subject: Re: [PATCH][RESEND for 2.6.29-rc8-mm1] skip I_CLEAR state inodes

On Wed, Apr 01, 2009 at 07:43:32AM +0800, Andrew Morton wrote:
> On Mon, 30 Mar 2009 15:18:24 +0800
> Wu Fengguang <fengguang.wu@...el.com> wrote:
>
> > clear_inode() will switch inode state from I_FREEING to I_CLEAR,
> > and do so _outside_ of inode_lock. So any I_FREEING testing is
> > incomplete without a coupled testing of I_CLEAR.
> >
> > So add I_CLEAR tests to drop_pagecache_sb(), generic_sync_sb_inodes() and
> > add_dquot_ref().
> >
> > Masayoshi MIZUMA discovered the bug in drop_pagecache_sb() and Jan Kara
> > reminds fixing the other two cases.
>
> ok...
>
> But what is the user-visible consequence of this?  You cc'ed
> stable@...nel.org so I assume it's serious.  People will want to know
> what problem we're fixing!

Sorry, the changelog could be expanded with the following paragraph:

Fix real kernel panics.  Masayoshi MIZUMA has a nice panic flow:
----------------------------------------------------------------------
            [process A]               |        [process B]
 |                                    |
 |    prune_icache()                  | drop_pagecache()
 |      spin_lock(&inode_lock)        |   drop_pagecache_sb()
 |      inode->i_state |= I_FREEING;  |       |
 |      spin_unlock(&inode_lock)      |       V
 |          |                         |     spin_lock(&inode_lock)
 |          V                         |         |
 |      dispose_list()                |         |
 |        list_del()                  |         |
 |        clear_inode()               |         |
 |          inode->i_state = I_CLEAR  |         |
 |            |                       |         V
 |            |                       |      if (inode->i_state & (I_FREEING|I_WILL_FREE))
 |            |                       |              continue;           <==== NOT MATCH
 |            |                       |
 |            |                       | (DANGER from here on! Accessing disposing inode!)
 |            |                       |
 |            |                       |      __iget()
 |            |                       |        list_move() <===== PANIC on poisoned list !!
 V            V                       |
(time)
----------------------------------------------------------------------

Thanks,
Fengguang

> >
> > --- mm.orig/fs/drop_caches.c
> > +++ mm/fs/drop_caches.c
> > @@ -18,7 +18,7 @@ static void drop_pagecache_sb(struct sup
> >
> >  	spin_lock(&inode_lock);
> >  	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
> > -		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
> > +		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
> >  			continue;
> >  		if (inode->i_mapping->nrpages == 0)
> >  			continue;
> > --- mm.orig/fs/fs-writeback.c
> > +++ mm/fs/fs-writeback.c
> > @@ -538,7 +538,8 @@ void generic_sync_sb_inodes(struct super
> >  		list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
> >  			struct address_space *mapping;
> >
> > -			if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
> > +			if (inode->i_state &
> > +					(I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
> >  				continue;
> >  			mapping = inode->i_mapping;
> >  			if (mapping->nrpages == 0)
> > --- mm.orig/fs/quota/dquot.c
> > +++ mm/fs/quota/dquot.c
> > @@ -823,7 +823,7 @@ static void add_dquot_ref(struct super_b
> >
> >  	spin_lock(&inode_lock);
> >  	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
> > -		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
> > +		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
> >  			continue;
> >  		if (!atomic_read(&inode->i_writecount))
> >  			continue;
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