Re: [PATCH v3] fs: clear writeback errors in inode_init_always

[Brian Foster <bfoster@redhat.com>]

On Tue, May 22, 2018 at 09:43:59AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> In inode_init_always(), we clear the inode mapping flags, which clears
> any retained error (AS_EIO, AS_ENOSPC) bits.  Unfortunately, we do not
> also clear wb_err, which means that old mapping errors can leak through
> to new inodes.
> 
> This is crucial for the XFS inode allocation path because we recycle old
> in-core inodes and we do not want error state from an old file to leak
> into the new file.  This bug was discovered by running generic/036 and
> generic/047 in a loop and noticing that the EIOs generated by the
> collision of direct and buffered writes in generic/036 would survive the
> remount between 036 and 047, and get reported to the fsyncs (on
> different files!) in generic/047.
> 
> Since we're changing the semantics of inode_init_always, we must also
> change xfs_reinit_inode to retain the writeback error state when we go
> to recover an inode that has been torn down in the vfs but not yet
> disposed of by XFS.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> ---
> v3: clear error state when allocating new inode
> v2: retain AS_EIO/AS_ENOSPC across xfs inode reinit
> ---
>  fs/inode.c          |    1 +
>  fs/xfs/xfs_icache.c |    9 +++++++++
>  fs/xfs/xfs_inode.c  |    5 +++++
>  3 files changed, 15 insertions(+)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 13ceb98c3bd3..3b55391072f3 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -178,6 +178,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
>  	mapping->a_ops = &empty_aops;
>  	mapping->host = inode;
>  	mapping->flags = 0;
> +	mapping->wb_err = 0;
>  	atomic_set(&mapping->i_mmap_writable, 0);
>  	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
>  	mapping->private_data = NULL;
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index 164350d91efc..d01f9544ff01 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -298,6 +298,10 @@ xfs_reinit_inode(
>  	uint64_t	version = inode_peek_iversion(inode);
>  	umode_t		mode = inode->i_mode;
>  	dev_t		dev = inode->i_rdev;
> +	errseq_t	old_err = inode->i_mapping->wb_err;
> +	bool		as_eio = test_bit(AS_EIO, &inode->i_mapping->flags);
> +	bool		as_enospc = test_bit(AS_ENOSPC,
> +					     &inode->i_mapping->flags);
>  
>  	error = inode_init_always(mp->m_super, inode);
>  
> @@ -306,6 +310,11 @@ xfs_reinit_inode(
>  	inode_set_iversion_queried(inode, version);
>  	inode->i_mode = mode;
>  	inode->i_rdev = dev;
> +	inode->i_mapping->wb_err = old_err;
> +	if (as_eio)
> +		set_bit(AS_EIO, &inode->i_mapping->flags);
> +	if (as_enospc)
> +		set_bit(AS_ENOSPC, &inode->i_mapping->flags);
>  	return error;
>  }
>  
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 02eae5059231..6c47ea3e577b 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -835,6 +835,11 @@ xfs_ialloc(
>  			inode->i_mode |= S_ISGID;
>  	}
>  
> +	/* Reset all vfs error state. */

I'd prefer a comment that reminds why we have to do this. E.g.,
something like:

	/*
	 * In-core inode reinit carries over vfs error state. Reset it
	 * so we don't leak error state from a previous generation of
	 * the inode.
	 */

... but feel free to reword that.

> +	inode->i_mapping->wb_err = 0;
> +	clear_bit(AS_EIO, &inode->i_mapping->flags);
> +	clear_bit(AS_ENOSPC, &inode->i_mapping->flags);
> +

I also wonder whether it might be cleaner to just reset this stuff in
xfs_ifree() where we kill the i_mode and bump the gen and whatnot, but
afaict this should work too. With the comment fix, at least:

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  	/*
>  	 * If the group ID of the new file does not match the effective group
>  	 * ID or one of the supplementary group IDs, the S_ISGID bit is cleared
> --
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