Btrfs: fix snapshot vs nocow writting (e9894fd3) · Commits · 戴 / test

While running fsstress and snapshots concurrently, we will hit something like followings: Thread 1 Thread 2 |->fallocate |->write pages |->join transaction |->add ordered extent |->end transaction |->flushing data |->creating pending snapshots |->write data into src root's fallocated space After above work flows finished, we will get a state that source and snapshot root share same space, but source root have written data into fallocated space, this will make fsck fail to verify checksums for snapshot root's preallocating file extent data.Nocow writting also has this same problem. Fix this problem by syncing snapshots with nocow writting: 1.for nocow writting,if there are pending snapshots, we will fall into COW way. 2.if there are pending nocow writes, snapshots for this root will be blocked until nocow writting finish. Reported-by:

Gui Hecheng <guihc.fnst@cn.fujitsu.com> Signed-off-by:

Wang Shilong <wangsl.fnst@cn.fujitsu.com> Signed-off-by:

Chris Mason <clm@fb.com>

fs/btrfs/inode.c

+21 −2

Original line number	Diff line number	Diff line
		@@ -1270,6 +1270,15 @@ next_slot:
		disk_bytenr += extent_offset;
		disk_bytenr += cur_offset - found_key.offset;
		num_bytes = min(end + 1, extent_end) - cur_offset;
		/*
		* if there are pending snapshots for this root,
		* we fall into common COW way.
		*/
		if (!nolock) {
		err = btrfs_start_nocow_write(root);
		if (!err)
		goto out_check;
		}
		/*
		* force cow if csum exists in the range.
		* this ensure that csum for a given extent are
		@@ -1289,6 +1298,8 @@ next_slot:
		out_check:
		if (extent_end <= start) {
		path->slots[0]++;
		if (!nolock && nocow)
		btrfs_end_nocow_write(root);
		goto next_slot;
		}
		if (!nocow) {
		@@ -1306,8 +1317,11 @@ out_check:
		ret = cow_file_range(inode, locked_page,
		cow_start, found_key.offset - 1,
		page_started, nr_written, 1);
		if (ret)
		if (ret) {
		if (!nolock && nocow)
		btrfs_end_nocow_write(root);
		goto error;
		}
		cow_start = (u64)-1;
		}

		@@ -1354,15 +1368,20 @@ out_check:
		BTRFS_DATA_RELOC_TREE_OBJECTID) {
		ret = btrfs_reloc_clone_csums(inode, cur_offset,
		num_bytes);
		if (ret)
		if (ret) {
		if (!nolock && nocow)
		btrfs_end_nocow_write(root);
		goto error;
		}
		}

		extent_clear_unlock_delalloc(inode, cur_offset,
		cur_offset + num_bytes - 1,
		locked_page, EXTENT_LOCKED \|
		EXTENT_DELALLOC, PAGE_UNLOCK \|
		PAGE_SET_PRIVATE2);
		if (!nolock && nocow)
		btrfs_end_nocow_write(root);
		cur_offset = extent_end;
		if (cur_offset > end)
		break;

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