Revert "iomap: write iomap validity checks"

This reverts commit 54a37e5d07 which is
commit d7b6404116 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I8df6cb973e6b4bc0acdb60fe95d45951354364dd
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

fs/iomap/buffered-io.c

@@ -579,7 +579,7 @@ static int iomap_write_begin_inline(const struct iomap_iter *iter,
 	return iomap_read_inline_data(iter, folio);
 }
 
-static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
+static int iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
 		size_t len, struct folio **foliop)
 {
 	const struct iomap_page_ops *page_ops = iter->iomap.page_ops;
@@ -613,27 +613,6 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
 		status = (iter->flags & IOMAP_NOWAIT) ? -EAGAIN : -ENOMEM;
 		goto out_no_page;
 	}
-
-	/*
-	 * Now we have a locked folio, before we do anything with it we need to
-	 * check that the iomap we have cached is not stale. The inode extent
-	 * mapping can change due to concurrent IO in flight (e.g.
-	 * IOMAP_UNWRITTEN state can change and memory reclaim could have
-	 * reclaimed a previously partially written page at this index after IO
-	 * completion before this write reaches this file offset) and hence we
-	 * could do the wrong thing here (zero a page range incorrectly or fail
-	 * to zero) and corrupt data.
-	 */
-	if (page_ops && page_ops->iomap_valid) {
-		bool iomap_valid = page_ops->iomap_valid(iter->inode,
-							&iter->iomap);
-		if (!iomap_valid) {
-			iter->iomap.flags |= IOMAP_F_STALE;
-			status = 0;
-			goto out_unlock;
-		}
-	}
-
 	if (pos + len > folio_pos(folio) + folio_size(folio))
 		len = folio_pos(folio) + folio_size(folio) - pos;
 
@@ -789,8 +768,6 @@ again:
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (unlikely(status))
 			break;
-		if (iter->iomap.flags & IOMAP_F_STALE)
-			break;
 
 		page = folio_file_page(folio, pos >> PAGE_SHIFT);
 		if (mapping_writably_mapped(mapping))
@@ -1099,8 +1076,6 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (unlikely(status))
 			return status;
-		if (iter->iomap.flags & IOMAP_F_STALE)
-			break;
 
 		status = iomap_write_end(iter, pos, bytes, bytes, folio);
 		if (WARN_ON_ONCE(status == 0))
@@ -1156,8 +1131,6 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (status)
 			return status;
-		if (iter->iomap.flags & IOMAP_F_STALE)
-			break;
 
 		offset = offset_in_folio(folio, pos);
 		if (bytes > folio_size(folio) - offset)

fs/iomap/iter.c

@@ -7,28 +7,12 @@
 #include <linux/iomap.h>
 #include "trace.h"
 
-/*
- * Advance to the next range we need to map.
- *
- * If the iomap is marked IOMAP_F_STALE, it means the existing map was not fully
- * processed - it was aborted because the extent the iomap spanned may have been
- * changed during the operation. In this case, the iteration behaviour is to
- * remap the unprocessed range of the iter, and that means we may need to remap
- * even when we've made no progress (i.e. iter->processed = 0). Hence the
- * "finished iterating" case needs to distinguish between
- * (processed = 0) meaning we are done and (processed = 0 && stale) meaning we
- * need to remap the entire remaining range.
- */
 static inline int iomap_iter_advance(struct iomap_iter *iter)
 {
-	bool stale = iter->iomap.flags & IOMAP_F_STALE;
-
 	/* handle the previous iteration (if any) */
 	if (iter->iomap.length) {
-		if (iter->processed < 0)
+		if (iter->processed <= 0)
 			return iter->processed;
-		if (!iter->processed && !stale)
-			return 0;
 		if (WARN_ON_ONCE(iter->processed > iomap_length(iter)))
 			return -EIO;
 		iter->pos += iter->processed;
@@ -49,7 +33,6 @@ static inline void iomap_iter_done(struct iomap_iter *iter)
 	WARN_ON_ONCE(iter->iomap.offset > iter->pos);
 	WARN_ON_ONCE(iter->iomap.length == 0);
 	WARN_ON_ONCE(iter->iomap.offset + iter->iomap.length <= iter->pos);
-	WARN_ON_ONCE(iter->iomap.flags & IOMAP_F_STALE);
 
 	trace_iomap_iter_dstmap(iter->inode, &iter->iomap);
 	if (iter->srcmap.type != IOMAP_HOLE)

include/linux/iomap.h

@@ -50,35 +50,26 @@ struct vm_fault;
  *
  * IOMAP_F_BUFFER_HEAD indicates that the file system requires the use of
  * buffer heads for this mapping.
- *
- * IOMAP_F_XATTR indicates that the iomap is for an extended attribute extent
- * rather than a file data extent.
  */
-#define IOMAP_F_NEW		(1U << 0)
-#define IOMAP_F_DIRTY		(1U << 1)
-#define IOMAP_F_SHARED		(1U << 2)
-#define IOMAP_F_MERGED		(1U << 3)
-#define IOMAP_F_BUFFER_HEAD	(1U << 4)
-#define IOMAP_F_ZONE_APPEND	(1U << 5)
-#define IOMAP_F_XATTR		(1U << 6)
+#define IOMAP_F_NEW		0x01
+#define IOMAP_F_DIRTY		0x02
+#define IOMAP_F_SHARED		0x04
+#define IOMAP_F_MERGED		0x08
+#define IOMAP_F_BUFFER_HEAD	0x10
+#define IOMAP_F_ZONE_APPEND	0x20
 
 /*
  * Flags set by the core iomap code during operations:
  *
  * IOMAP_F_SIZE_CHANGED indicates to the iomap_end method that the file size
  * has changed as the result of this write operation.
- *
- * IOMAP_F_STALE indicates that the iomap is not valid any longer and the file
- * range it covers needs to be remapped by the high level before the operation
- * can proceed.
  */
-#define IOMAP_F_SIZE_CHANGED	(1U << 8)
-#define IOMAP_F_STALE		(1U << 9)
+#define IOMAP_F_SIZE_CHANGED	0x100
 
 /*
  * Flags from 0x1000 up are for file system specific usage:
  */
-#define IOMAP_F_PRIVATE		(1U << 12)
+#define IOMAP_F_PRIVATE		0x1000
 
 
 /*
@@ -99,7 +90,6 @@ struct iomap {
 	void			*inline_data;
 	void			*private; /* filesystem private */
 	const struct iomap_page_ops *page_ops;
-	u64			validity_cookie; /* used with .iomap_valid() */
 
 	ANDROID_KABI_RESERVE(1);
 };
@@ -141,23 +131,6 @@ struct iomap_page_ops {
 	int (*page_prepare)(struct inode *inode, loff_t pos, unsigned len);
 	void (*page_done)(struct inode *inode, loff_t pos, unsigned copied,
 			struct page *page);
-
-	/*
-	 * Check that the cached iomap still maps correctly to the filesystem's
-	 * internal extent map. FS internal extent maps can change while iomap
-	 * is iterating a cached iomap, so this hook allows iomap to detect that
-	 * the iomap needs to be refreshed during a long running write
-	 * operation.
-	 *
-	 * The filesystem can store internal state (e.g. a sequence number) in
-	 * iomap->validity_cookie when the iomap is first mapped to be able to
-	 * detect changes between mapping time and whenever .iomap_valid() is
-	 * called.
-	 *
-	 * This is called with the folio over the specified file position held
-	 * locked by the iomap code.
-	 */
-	bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap);
 };
 
 /*