[PATCH v2] xfs: shutdown on failure to add page to log bio

[PATCH v2] xfs: shutdown on failure to add page to log bio

[Brian Foster]

If the bio_add_page() call fails, we proceed to write out a
partially constructed log buffer. This corrupts the physical log
such that log recovery is not possible. Worse, persistent
occurrences of this error eventually lead to a BUG_ON() failure in
bio_split() as iclogs wrap the end of the physical log, which
triggers log recovery on subsequent mount.

Rather than warn about writing out a corrupted log buffer, shutdown
the fs as is done for any log I/O related error. This preserves the
consistency of the physical log such that log recovery succeeds on a
subsequent mount. Note that this was observed on a 64k page debug
kernel without upstream commit 59bb47985c1d ("mm, sl[aou]b:
guarantee natural alignment for kmalloc(power-of-two)"), which
demonstrated frequent iclog bio overflows due to unaligned (slab
allocated) iclog data buffers.

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

v2:
- Refactor to keep xlog_map_iclog_data() generic and prevent bio
  submission.
v1: https://lore.kernel.org/linux-xfs/20200324165700.7575-1-bfoster@redhat.com/

 fs/xfs/xfs_log.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 2a90a483c2d6..4a53768c5397 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1703,7 +1703,7 @@ xlog_bio_end_io(
 		   &iclog->ic_end_io_work);
 }
 
-static void
+static int
 xlog_map_iclog_data(
 	struct bio		*bio,
 	void			*data,
@@ -1714,11 +1714,14 @@ xlog_map_iclog_data(
 		unsigned int	off = offset_in_page(data);
 		size_t		len = min_t(size_t, count, PAGE_SIZE - off);
 
-		WARN_ON_ONCE(bio_add_page(bio, page, len, off) != len);
+		if (bio_add_page(bio, page, len, off) != len)
+			return -EIO;
 
 		data += len;
 		count -= len;
 	} while (count);
+
+	return 0;
 }
 
 STATIC void
@@ -1762,7 +1765,10 @@ xlog_write_iclog(
 	if (need_flush)
 		iclog->ic_bio.bi_opf |= REQ_PREFLUSH;
 
-	xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count);
+	if (xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count)) {
+		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
+		return;
+	}
 	if (is_vmalloc_addr(iclog->ic_data))
 		flush_kernel_vmap_range(iclog->ic_data, count);
 
-- 
2.21.1

Re: [PATCH v2] xfs: shutdown on failure to add page to log bio

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>