[PATCH 4/4] ext4: initialize map->m_pblk in ext4_da_map_blocks()

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

ext4_da_map_blocks() returns a delalloc mapping through @map without
touching map->m_pblk at all. Callers that only set up m_lblk and m_len
of their local struct ext4_map_blocks and leave the rest to the mapping
helper, like ext4_iomap_map_blocks() does, end up with whatever happened
to be on their stack, so the trace_ext4_iomap_buffered_write_begin()
tracepoint prints an uninitialized pblk for a delalloc mapping.

This has been harmless so far, ext4_da_get_block_prep() and
ext4_set_iomap() both ignore m_pblk for a delalloc mapping, only the new
tracepoint dumps it.

Initialize m_pblk along with m_flags at the beginning of
ext4_da_map_blocks(), so that a delalloc mapping is always reported with
pblk 0, the same way ext4_map_blocks() reports it.

Fixes: 008f019ab559 ("ext4: add block mapping tracepoints for iomap buffered I/O path")
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/ext4/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6b2f1b07f41e6..c1c46e86bba3e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2041,6 +2041,7 @@ static int ext4_da_map_blocks(struct inode *inode, struct ext4_map_blocks *map)
 #endif
 
 	map->m_flags = 0;
+	map->m_pblk = 0;
 	ext_debug(inode, "max_blocks %u, logical block %lu\n", map->m_len,
 		  (unsigned long) map->m_lblk);
 
-- 
2.52.0