linux-kernel - Re: The bug of iput() removal from flusher thread?

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Message-ID: <20121121014851.GH10507@quack.suse.cz>
Date:	Wed, 21 Nov 2012 02:48:51 +0100
From:	Jan Kara <jack@...e.cz>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: The bug of iput() removal from flusher thread?

On Wed 21-11-12 02:11:11, Jan Kara wrote:
> On Tue 20-11-12 06:53:12, OGAWA Hirofumi wrote:
> > Jan Kara <jack@...e.cz> writes:
> > 
> > >> >  static void inode_sync_complete(struct inode *inode)
> > >> >  {
> > >> > +	/* If inode is clean an unused, put it into LRU now.  */
> > >> > +	if (!(inode->i_state & I_DIRTY) && !atomic_read(&inode->i_count))
> > >> > +		inode_lru_list_add(inode);
> > >> 
> > >> IMHO, open coding this would be bad idea.
> > >   Do you mean creating a separate function for the above two lines?
> > 
> > Yes. And the intent is to consolidate "when adds inode to LRU" with
> > iput_final()'s one.
> > 
> > >> And another one is I_REFERENCED. We really want to remove I_REFERENCED?
> > >   We don't want I_REFERENCED set - noone used the inode. But looking into
> > > the code with fresh eyes, the fix isn't as simple as I thought. First I
> > > need to check MS_ACTIVE and second I need to check I_FREEING... So the
> > > condition will be complex enough to warrant a separate function.
> > 
> > I can't see the issue (sync_filesystem() will wait I_DIRTY before
> > MS_ACTIVE, and I_DIRTY prevents I_FREEING) though, it may be possible.
>   E.g. when inode is deleted it can be both I_DIRTY (and flusher thread
> can be working on it) while it is also marked as I_FREEING. In such case we
> must avoid adding the inode to the LRU.
> 
>   Regarding MS_ACTIVE - you are right that sync_filesystem() should clean
> all dirty inodes but some filesystems dirty their internal inodes during
> umount so it's better to make flusher thread safe and not add such inodes
> to the LRU during umount.
  Here's the patch I currently have BTW.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-writeback-Put-unused-inodes-to-LRU-after-writeback-c.patch" of type "text/x-patch" (3343 bytes)