Patch "btrfs: Remove false alert when fiemap range is smaller than on-disk extent" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

btrfs: Remove false alert when fiemap range is smaller than on-disk extent

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-remove-false-alert-when-fiemap-range-is-smaller-than-on-disk-extent.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Qu Wenruo <[email protected]>
Date: Thu, 22 Jun 2017 10:01:21 +0800
Subject: btrfs: Remove false alert when fiemap range is smaller than on-disk extent

From: Qu Wenruo <[email protected]>

commit 848c23b78fafdcd3270b06a30737f8dbd70c347f upstream.

Commit 4751832da990 ("btrfs: fiemap: Cache and merge fiemap extent before submit it to user") introduced a warning to catch unemitted cached fiemap extent.

However such warning doesn't take the following case into consideration:

0 4K 8K

|<---- fiemap range --->|
|<----------- On-disk extent ------------------>|

In this case, the whole 0~8K is cached, and since it's larger than fiemap range, it break the fiemap extent emit loop.
This leaves the fiemap extent cached but not emitted, and caught by the final fiemap extent sanity check, causing kernel warning.

This patch removes the kernel warning and renames the sanity check to emit_last_fiemap_cache() since it's possible and valid to have cached fiemap extent.

---
 fs/btrfs/extent_io.c |   28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

@@ -4463,29 +4463,25 @@ try_submit_last:
 }
 
 /*
- * Sanity check for fiemap cache
+ * Emit last fiemap cache
  *
- * All fiemap cache should be submitted by emit_fiemap_extent()
- * Iteration should be terminated either by last fiemap extent or
- * fieinfo->fi_extents_max.
- * So no cached fiemap should exist.
+ * The last fiemap cache may still be cached in the following case:
+ * 0		      4k		    8k
+ * |<- Fiemap range ->|
+ * |<------------  First extent ----------->|
+ *
+ * In this case, the first extent range will be cached but not emitted.
+ * So we must emit it before ending extent_fiemap().
  */
-static int check_fiemap_cache(struct btrfs_fs_info *fs_info,
-			       struct fiemap_extent_info *fieinfo,
-			       struct fiemap_cache *cache)
+static int emit_last_fiemap_cache(struct btrfs_fs_info *fs_info,
+				  struct fiemap_extent_info *fieinfo,
+				  struct fiemap_cache *cache)
 {
 	int ret;
 
 	if (!cache->cached)
 		return 0;
 
-	/* Small and recoverbale problem, only to info developer */
-#ifdef CONFIG_BTRFS_DEBUG
-	WARN_ON(1);
-#endif
-	btrfs_warn(fs_info,
-		   "unhandled fiemap cache detected: offset=%llu phys=%llu len=%llu flags=0x%x",
-		   cache->offset, cache->phys, cache->len, cache->flags);
 	ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
 				      cache->len, cache->flags);
 	cache->cached = false;

@@ -4701,7 +4697,7 @@ int extent_fiemap(struct inode *inode, s
 	}
 out_free:
 	if (!ret)
-		ret = check_fiemap_cache(root->fs_info, fieinfo, &cache);
+		ret = emit_last_fiemap_cache(root->fs_info, fieinfo, &cache);
 	free_extent_map(em);
 out:
 	btrfs_free_path(path);

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/btrfs-remove-false-alert-when-fiemap-range-is-smaller-than-on-disk-extent.patch