[PATCH 2/2] iomap: fall back to buffered writes for invalidation failures

[Christoph Hellwig <hch@lst.de>]

Failing to invalid the page cache means data in incoherent, which is
a very bad state for the system.  Always fall back to buffered I/O
through the page cache if we can't invalidate mappings.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/ext4/file.c       |  2 ++
 fs/gfs2/file.c       |  3 ++-
 fs/iomap/direct-io.c | 13 ++++++++-----
 fs/iomap/trace.h     |  1 +
 fs/xfs/xfs_file.c    |  4 ++--
 fs/zonefs/super.c    |  7 +++++--
 6 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 2a01e31a032c4c..0da6c2a2c32c1e 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -544,6 +544,8 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		iomap_ops = &ext4_iomap_overwrite_ops;
 	ret = iomap_dio_rw(iocb, from, iomap_ops, &ext4_dio_write_ops,
 			   is_sync_kiocb(iocb) || unaligned_io || extend);
+	if (ret == -EREMCHG)
+		ret = 0;
 
 	if (extend)
 		ret = ext4_handle_inode_extension(inode, offset, ret, count);
diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index fe305e4bfd3734..c7907d40c61d17 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -814,7 +814,8 @@ static ssize_t gfs2_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 
 	ret = iomap_dio_rw(iocb, from, &gfs2_iomap_ops, NULL,
 			   is_sync_kiocb(iocb));
-
+	if (ret == -EREMCHG)
+		ret = 0;
 out:
 	gfs2_glock_dq(&gh);
 out_uninit:
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 190967e87b69e4..62626235cdbe8d 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -10,6 +10,7 @@
 #include <linux/backing-dev.h>
 #include <linux/uio.h>
 #include <linux/task_io_accounting_ops.h>
+#include "trace.h"
 
 #include "../internal.h"
 
@@ -478,13 +479,15 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	if (iov_iter_rw(iter) == WRITE) {
 		/*
 		 * Try to invalidate cache pages for the range we are writing.
-		 * If this invalidation fails, tough, the write will still work,
-		 * but racing two incompatible write paths is a pretty crazy
-		 * thing to do, so we don't support it 100%.
+		 * If this invalidation fails, let the caller fall back to
+		 * buffered I/O.
 		 */
 		if (invalidate_inode_pages2_range(mapping, pos >> PAGE_SHIFT,
-				end >> PAGE_SHIFT))
-			dio_warn_stale_pagecache(iocb->ki_filp);
+				end >> PAGE_SHIFT)) {
+			trace_iomap_dio_invalidate_fail(inode, pos, count);
+			ret = -EREMCHG;
+			goto out_free_dio;
+		}
 
 		if (!wait_for_completion && !inode->i_sb->s_dio_done_wq) {
 			ret = sb_init_dio_done_wq(inode->i_sb);
diff --git a/fs/iomap/trace.h b/fs/iomap/trace.h
index 5693a39d52fb63..fdc7ae388476f5 100644
--- a/fs/iomap/trace.h
+++ b/fs/iomap/trace.h
@@ -74,6 +74,7 @@ DEFINE_EVENT(iomap_range_class, name,	\
 DEFINE_RANGE_EVENT(iomap_writepage);
 DEFINE_RANGE_EVENT(iomap_releasepage);
 DEFINE_RANGE_EVENT(iomap_invalidatepage);
+DEFINE_RANGE_EVENT(iomap_dio_invalidate_fail);
 
 #define IOMAP_TYPE_STRINGS \
 	{ IOMAP_HOLE,		"HOLE" }, \
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 00db81eac80d6c..551cca39fa3ba6 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -553,8 +553,8 @@ xfs_file_dio_aio_write(
 	xfs_iunlock(ip, iolock);
 
 	/*
-	 * No fallback to buffered IO on errors for XFS, direct IO will either
-	 * complete fully or fail.
+	 * No partial fallback to buffered IO on errors for XFS, direct IO will
+	 * either complete fully or fail.
 	 */
 	ASSERT(ret < 0 || ret == count);
 	return ret;
diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c
index 07bc42d62673ce..793850454b752f 100644
--- a/fs/zonefs/super.c
+++ b/fs/zonefs/super.c
@@ -786,8 +786,11 @@ static ssize_t zonefs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (iocb->ki_pos >= ZONEFS_I(inode)->i_max_size)
 		return -EFBIG;
 
-	if (iocb->ki_flags & IOCB_DIRECT)
-		return zonefs_file_dio_write(iocb, from);
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		ret = zonefs_file_dio_write(iocb, from);
+		if (ret != -EREMCHG)
+			return ret;
+	}
 
 	return zonefs_file_buffered_write(iocb, from);
 }
-- 
2.26.2