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

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, May 22, 2018 at 02:40:09PM -0400, Brian Foster wrote:
> 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.
> 	 */

I settled on:

	/*
	 * In-core inode reinit does not clear 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>

Thanks for the review!

--D

> 
> >  	/*
> >  	 * 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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