[PATCH v2 2/3] fs: keep dio_warn_stale_pagecache() when CONFIG_BLOCK=n

[Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>]

This helper prints warning if direct I/O write failed to invalidate cache,
and set EIO at inode to warn usersapce about possible data corruption.
See also commit 5a9d929d6e13 ("iomap: report collisions between directio and
buffered writes to userspace").

Direct I/O is supported by non-disk filesystems, for example NFS.
Thus generic code needs this even in kernel without CONFIG_BLOCK.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
 fs/direct-io.c     |   21 ---------------------
 include/linux/fs.h |    6 +++++-
 mm/filemap.c       |   21 +++++++++++++++++++++
 3 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 9329ced91f1d..0ec4f270139f 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -220,27 +220,6 @@ static inline struct page *dio_get_page(struct dio *dio,
 	return dio->pages[sdio->head];
 }
 
-/*
- * Warn about a page cache invalidation failure during a direct io write.
- */
-void dio_warn_stale_pagecache(struct file *filp)
-{
-	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
-	char pathname[128];
-	struct inode *inode = file_inode(filp);
-	char *path;
-
-	errseq_set(&inode->i_mapping->wb_err, -EIO);
-	if (__ratelimit(&_rs)) {
-		path = file_path(filp, pathname, sizeof(pathname));
-		if (IS_ERR(path))
-			path = "(unknown)";
-		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
-		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
-			current->comm);
-	}
-}
-
 /*
  * dio_complete() - called when all DIO BIO I/O has been completed
  *
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e0d909d35763..b4e4560d1c38 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3153,7 +3153,6 @@ enum {
 };
 
 void dio_end_io(struct bio *bio);
-void dio_warn_stale_pagecache(struct file *filp);
 
 ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 			     struct block_device *bdev, struct iov_iter *iter,
@@ -3198,6 +3197,11 @@ static inline void inode_dio_end(struct inode *inode)
 		wake_up_bit(&inode->i_state, __I_DIO_WAKEUP);
 }
 
+/*
+ * Warn about a page cache invalidation failure diring a direct I/O write.
+ */
+void dio_warn_stale_pagecache(struct file *filp);
+
 extern void inode_set_flags(struct inode *inode, unsigned int flags,
 			    unsigned int mask);
 
diff --git a/mm/filemap.c b/mm/filemap.c
index 288e38199068..189b8f318da2 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3161,6 +3161,27 @@ int pagecache_write_end(struct file *file, struct address_space *mapping,
 }
 EXPORT_SYMBOL(pagecache_write_end);
 
+/*
+ * Warn about a page cache invalidation failure during a direct I/O write.
+ */
+void dio_warn_stale_pagecache(struct file *filp)
+{
+	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
+	char pathname[128];
+	struct inode *inode = file_inode(filp);
+	char *path;
+
+	errseq_set(&inode->i_mapping->wb_err, -EIO);
+	if (__ratelimit(&_rs)) {
+		path = file_path(filp, pathname, sizeof(pathname));
+		if (IS_ERR(path))
+			path = "(unknown)";
+		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
+		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
+			current->comm);
+	}
+}
+
 ssize_t
 generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 {