From: Minchan Kim <minc...@kernel.org>

commit 8b7b2eb131d3476062ffd34358785b44be25172f upstream.

The swap address_space doesn't have host. Thus, it makes kernel crash once
swap write meets error. Fix it.

Fixes: 735e4ae5ba28 ("vfs: track per-sb writeback errors and report them to 
syncfs")
Signed-off-by: Minchan Kim <minc...@kernel.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Acked-by: Jeff Layton <jlay...@kernel.org>
Cc: Jan Kara <j...@suse.cz>
Cc: Andres Freund <and...@anarazel.de>
Cc: Matthew Wilcox <wi...@infradead.org>
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Christoph Hellwig <h...@infradead.org>
Cc: Dave Chinner <da...@fromorbit.com>
Cc: David Howells <dhowe...@redhat.com>
Cc: <sta...@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201010000650.750063-1-minc...@kernel.org
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 include/linux/pagemap.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -54,7 +54,8 @@ static inline void mapping_set_error(str
        __filemap_set_wb_err(mapping, error);
 
        /* Record it in superblock */
-       errseq_set(&mapping->host->i_sb->s_wb_err, error);
+       if (mapping->host)
+               errseq_set(&mapping->host->i_sb->s_wb_err, error);
 
        /* Record it in flags for now, for legacy callers */
        if (error == -ENOSPC)


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