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

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jeff Layton <jlayton@kernel.org>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	linux-fsdevel@vger.kernel.org, fstests@vger.kernel.org,
	xfs <linux-xfs@vger.kernel.org>
Subject: Re: [PATCH] fs: clear writeback errors in inode_init_always
Date: Mon, 21 May 2018 10:54:57 -0700	[thread overview]
Message-ID: <20180521175457.GI23858@magnolia> (raw)
In-Reply-To: <20180519153619.GA24698@bombadil.infradead.org>

On Sat, May 19, 2018 at 08:36:19AM -0700, Matthew Wilcox wrote:
> On Sat, May 19, 2018 at 08:27:00AM -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_ENOSC) bits.  Unfortunately, we do not
> 
> typo of ENOSPC in case you do a new version

Fixed, thanks.

> > 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 on a reformatted fs!) 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.
> 
> Don't you also need to preserve inode->i_mapping->flags across the
> reinitialisation for the users which aren't yet using ->wb_err?

At first I thought (mistakenly) that xfs had been completely converted,
but digging further we still use the old filemap_check_errors.  It seems
reasonable to me that if we're going to resurrect an incore inode then
we should try to hang on to AS_EIO/AS_ENOSPC for as long as we can.

--D

> > +++ b/fs/xfs/xfs_icache.c
> > @@ -298,6 +298,7 @@ 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;
> >  
> >  	error = inode_init_always(mp->m_super, inode);
> >  
> > @@ -306,6 +307,7 @@ xfs_reinit_inode(
> >  	inode_set_iversion_queried(inode, version);
> >  	inode->i_mode = mode;
> >  	inode->i_rdev = dev;
> > +	inode->i_mapping->wb_err = old_err;
> >  	return error;
> >  }
> >  
> --
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