linux-ext4 - Re: [PATCH 3/3] ext4: Gracefully handle ext4_break

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Date:   Tue, 21 May 2019 11:27:32 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/3] ext4: Gracefully handle ext4_break_layouts() failure
 during truncate

On Tue, May 21, 2019 at 09:43:58AM +0200, Jan Kara wrote:
> ext4_break_layouts() may fail e.g. due to a signal being delivered.
> Thus we need to handle its failure gracefully and not by taking the
> filesystem down. Currently ext4_break_layouts() failure is rare but it
> may become more common once RDMA uses layout leases for handling
> long-term page pins for DAX mappings.
> 
> To handle the failure we need to move ext4_break_layouts() earlier
> during setattr handling before we do hard to undo changes such as
> modifying inode size. To be able to do that we also have to move some
> other checks which are better done without holding i_mmap_sem earlier.
> 
> Reported-by: "Weiny, Ira" <ira.weiny@...el.com>
> Signed-off-by: Jan Kara <jack@...e.cz>


This fixes the bug I was seeing WRT ext4_break_layouts().  Thanks for the help!
One more NIT comment below.

> ---
>  fs/ext4/inode.c | 55 ++++++++++++++++++++++++++++---------------------------
>  1 file changed, 28 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index c7f77c643008..979570b42e18 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5571,7 +5571,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>  	if (attr->ia_valid & ATTR_SIZE) {
>  		handle_t *handle;
>  		loff_t oldsize = inode->i_size;
> -		int shrink = (attr->ia_size <= inode->i_size);
> +		int shrink = (attr->ia_size < inode->i_size);
>  
>  		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
>  			struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> @@ -5585,18 +5585,35 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>  		if (IS_I_VERSION(inode) && attr->ia_size != inode->i_size)
>  			inode_inc_iversion(inode);
>  
> -		if (ext4_should_order_data(inode) &&
> -		    (attr->ia_size < inode->i_size)) {
> -			error = ext4_begin_ordered_truncate(inode,
> +		if (shrink) {
> +			if (ext4_should_order_data(inode)) {
> +				error = ext4_begin_ordered_truncate(inode,
>  							    attr->ia_size);
> -			if (error)
> -				goto err_out;
> +				if (error)
> +					goto err_out;
> +			}
> +			/*
> +			 * Blocks are going to be removed from the inode. Wait
> +			 * for dio in flight.
> +			 */
> +			inode_dio_wait(inode);
> +		} else {
> +			pagecache_isize_extended(inode, oldsize, inode->i_size);
>  		}
> +
> +		down_write(&EXT4_I(inode)->i_mmap_sem);
> +
> +		rc = ext4_break_layouts(inode);
> +		if (rc) {
> +			up_write(&EXT4_I(inode)->i_mmap_sem);
> +			return rc;
> +		}
> +
>  		if (attr->ia_size != inode->i_size) {
>  			handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
>  			if (IS_ERR(handle)) {
>  				error = PTR_ERR(handle);
> -				goto err_out;
> +				goto out_mmap_sem;
>  			}
>  			if (ext4_handle_valid(handle) && shrink) {
>  				error = ext4_orphan_add(handle, inode);
> @@ -5627,29 +5644,12 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>  			if (error) {
>  				if (orphan && inode->i_nlink)
>  					ext4_orphan_del(NULL, inode);
> -				goto err_out;
> +				goto out_mmap_sem;

This goto flows through a second ext4_orphan_del() call which threw me at
first.  But I think this is ok.

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

And with the series applied.

Tested-by: Ira Weiny <ira.weiny@...el.com>

>  			}
>  		}
> -		if (!shrink) {
> -			pagecache_isize_extended(inode, oldsize, inode->i_size);
> -		} else {
> -			/*
> -			 * Blocks are going to be removed from the inode. Wait
> -			 * for dio in flight.
> -			 */
> -			inode_dio_wait(inode);
> -		}
> -		if (orphan && ext4_should_journal_data(inode))
> -			ext4_wait_for_tail_page_commit(inode);
> -		down_write(&EXT4_I(inode)->i_mmap_sem);
> -
> -		rc = ext4_break_layouts(inode);
> -		if (rc) {
> -			up_write(&EXT4_I(inode)->i_mmap_sem);
> -			error = rc;
> -			goto err_out;
> -		}
>  
> +		if (shrink && ext4_should_journal_data(inode))
> +			ext4_wait_for_tail_page_commit(inode);
>  		/*
>  		 * Truncate pagecache after we've waited for commit
>  		 * in data=journal mode to make pages freeable.
> @@ -5660,6 +5660,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>  			if (rc)
>  				error = rc;
>  		}
> +out_mmap_sem:
>  		up_write(&EXT4_I(inode)->i_mmap_sem);
>  	}
>  
> -- 
> 2.16.4
>