[Devel] [PATCH RH7 3/3] ext4: prevent partial update of the extent blocks

[Pavel Tikhomirov]

From: Zhang Yi <yi.zhang at huawei.com>

In the most error path of current extents updating operations are not
roll back partial updates properly when some bad things happens(.e.g in
ext4_ext_insert_extent()). So we may get an inconsistent extents tree
if journal has been aborted due to IO error, which may probability lead
to BUGON later when we accessing these extent entries in errors=continue
mode. This patch drop extent buffer's verify flag before updatng the
contents in ext4_ext_get_access(), and reset it after updating in
__ext4_ext_dirty(). After this patch we could force to check the extent
buffer if extents tree updating was break off, make sure the extents are
consistent.

Signed-off-by: Zhang Yi <yi.zhang at huawei.com>
Reviewed-by: Theodore Ts'o <tytso at mit.edu>
Link: https://lore.kernel.org/r/20210908120850.4012324-4-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso at mit.edu>

(cherry-picked from ms commit 0f2f87d51aebcf71a709b52f661d681594c7dffa)
https://jira.sw.ru/browse/PSBM-139452
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 fs/ext4/extents.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0b6ed085f3d9..52835f176015 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -140,14 +140,24 @@ static int ext4_ext_truncate_extend_restart(handle_t *handle,
 static int ext4_ext_get_access(handle_t *handle, struct inode *inode,
 				struct ext4_ext_path *path)
 {
+	int err = 0;
+
 	if (path->p_bh) {
 		/* path points to block */
 		BUFFER_TRACE(path->p_bh, "get_write_access");
-		return ext4_journal_get_write_access(handle, path->p_bh);
+		err = ext4_journal_get_write_access(handle, path->p_bh);
+		/*
+		 * The extent buffer's verified bit will be set again in
+		 * __ext4_ext_dirty(). We could leave an inconsistent
+		 * buffer if the extents updating procudure break off du
+		 * to some error happens, force to check it again.
+		 */
+		if (!err)
+			clear_buffer_verified(path->p_bh);
 	}
 	/* path points to leaf/index in inode body */
 	/* we use in-core data, no need to protect them */
-	return 0;
+	return err;
 }
 
 /*
@@ -167,6 +177,9 @@ int __ext4_ext_dirty(const char *where, unsigned int line, handle_t *handle,
 		/* path points to block */
 		err = __ext4_handle_dirty_metadata(where, line, handle,
 						   inode, path->p_bh);
+		/* Extents updating done, re-set verified flag */
+		if (!err)
+			set_buffer_verified(path->p_bh);
 	} else {
 		/* path points to leaf/index in inode body */
 		err = ext4_mark_inode_dirty(handle, inode);
-- 
2.35.3