linux-ext4 - Re: [PATCH 2/8] ext4: remove i_alloc

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Date:	Tue, 21 Jun 2011 18:48:13 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Lukas Czerner <lczerner@...hat.com>
cc:	Christoph Hellwig <hch@...radead.org>, viro@...iv.linux.org.uk,
	tglx@...utronix.de, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
	hirofumi@...l.parknet.co.jp, mfasheh@...e.com, jlbec@...lplan.org
Subject: Re: [PATCH 2/8] ext4: remove i_alloc_sem abuse

On Tue, 21 Jun 2011, Lukas Czerner wrote:

> On Mon, 20 Jun 2011, Christoph Hellwig wrote:
> 
> > Add a new rw_semaphore to protect page_mkwrite against truncate.  Previous
> > i_alloc_sem was abused for this, but it's going away in this series.
> > 
> > Signed-off-by: Christoph Hellwig <hch@....de>
> > 
> > Index: linux-2.6/fs/ext4/inode.c
> > ===================================================================
> > --- linux-2.6.orig/fs/ext4/inode.c	2011-06-20 14:25:33.779248128 +0200
> > +++ linux-2.6/fs/ext4/inode.c	2011-06-20 14:27:53.025907745 +0200
> > @@ -5357,6 +5357,7 @@ int ext4_setattr(struct dentry *dentry,
> >  			if (attr->ia_size > sbi->s_bitmap_maxbytes)
> >  				return -EFBIG;
> >  		}
> > +		down_write(&(EXT4_I(inode)->truncate_lock));
> >  	}
> >  
> >  	if (S_ISREG(inode->i_mode) &&
> > @@ -5405,6 +5406,9 @@ int ext4_setattr(struct dentry *dentry,
> >  			ext4_truncate(inode);
> >  	}
> >  
> > +	if (attr->ia_valid & ATTR_SIZE)
> > +		up_write(&(EXT4_I(inode)->truncate_lock));
> > +
> 
> Hi Christoph,
> 
> this looks like a bug fix, so we should rather do it in a separate
> commit. Could you send it separately, or at least mention that in commit
> description ?

That's stupid note, it is not a bugfix of course. Ignore it, sorry for
the noise.

> 
> Otherwise the patch looks good.
> 
> Thanks!
> -Lukas
> 
> >  	if (!rc) {
> >  		setattr_copy(inode, attr);
> >  		mark_inode_dirty(inode);
> > @@ -5850,10 +5854,10 @@ int ext4_page_mkwrite(struct vm_area_str
> >  	struct address_space *mapping = inode->i_mapping;
> >  
> >  	/*
> > -	 * Get i_alloc_sem to stop truncates messing with the inode. We cannot
> > -	 * get i_mutex because we are already holding mmap_sem.
> > +	 * Get truncate_lock to stop truncates messing with the inode. We
> > +	 * cannot get i_mutex because we are already holding mmap_sem.
> >  	 */
> > -	down_read(&inode->i_alloc_sem);
> > +	down_read(&(EXT4_I(inode)->truncate_lock));
> >  	size = i_size_read(inode);
> >  	if (page->mapping != mapping || size <= page_offset(page)
> >  	    || !PageUptodate(page)) {
> > @@ -5865,7 +5869,7 @@ int ext4_page_mkwrite(struct vm_area_str
> >  	lock_page(page);
> >  	wait_on_page_writeback(page);
> >  	if (PageMappedToDisk(page)) {
> > -		up_read(&inode->i_alloc_sem);
> > +		up_read(&(EXT4_I(inode)->truncate_lock));
> >  		return VM_FAULT_LOCKED;
> >  	}
> >  
> > @@ -5883,7 +5887,7 @@ int ext4_page_mkwrite(struct vm_area_str
> >  	if (page_has_buffers(page)) {
> >  		if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
> >  					ext4_bh_unmapped)) {
> > -			up_read(&inode->i_alloc_sem);
> > +			up_read(&(EXT4_I(inode)->truncate_lock));
> >  			return VM_FAULT_LOCKED;
> >  		}
> >  	}
> > @@ -5912,11 +5916,11 @@ int ext4_page_mkwrite(struct vm_area_str
> >  	 */
> >  	lock_page(page);
> >  	wait_on_page_writeback(page);
> > -	up_read(&inode->i_alloc_sem);
> > +	up_read(&(EXT4_I(inode)->truncate_lock));
> >  	return VM_FAULT_LOCKED;
> >  out_unlock:
> >  	if (ret)
> >  		ret = VM_FAULT_SIGBUS;
> > -	up_read(&inode->i_alloc_sem);
> > +	up_read(&(EXT4_I(inode)->truncate_lock));
> >  	return ret;
> >  }
> > Index: linux-2.6/fs/ext4/super.c
> > ===================================================================
> > --- linux-2.6.orig/fs/ext4/super.c	2011-06-20 14:25:33.795914793 +0200
> > +++ linux-2.6/fs/ext4/super.c	2011-06-20 14:27:06.269243443 +0200
> > @@ -871,6 +871,7 @@ static struct inode *ext4_alloc_inode(st
> >  	ei->i_datasync_tid = 0;
> >  	atomic_set(&ei->i_ioend_count, 0);
> >  	atomic_set(&ei->i_aiodio_unwritten, 0);
> > +	init_rwsem(&ei->truncate_lock);
> >  
> >  	return &ei->vfs_inode;
> >  }
> > Index: linux-2.6/fs/ext4/ext4.h
> > ===================================================================
> > --- linux-2.6.orig/fs/ext4/ext4.h	2011-06-20 14:25:33.752581461 +0200
> > +++ linux-2.6/fs/ext4/ext4.h	2011-06-20 14:27:06.272576777 +0200
> > @@ -844,6 +844,9 @@ struct ext4_inode_info {
> >  	/* on-disk additional length */
> >  	__u16 i_extra_isize;
> >  
> > +	/* protect page_mkwrite against truncates */
> > +	struct rw_semaphore truncate_lock;
> > +
> >  #ifdef CONFIG_QUOTA
> >  	/* quota space reservation, managed internally by quota code */
> >  	qsize_t i_reserved_quota;
> > 
> > --
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> > 
> 
> 

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