From 3f950867c307c5413d628a153ac44915bd117ffd Mon Sep 17 00:00:00 2001 From: Shuangpeng Bai Date: Sun, 5 Jul 2026 01:46:35 -0400 Subject: [PATCH] btrfs: fix extent map leak in NOCOW direct I/O write btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an extent map reference that must be dropped on all exit paths. For direct writes into a NOCOW range, btrfs_get_blocks_direct_write() keeps using that extent map and asks btrfs_create_dio_extent() to allocate the ordered extent. If that fails, for example because btrfs_alloc_ordered_extent() fails, the function returns the error without dropping the input extent map. The PREALLOC path avoided this by dropping the input extent map before replacing it with the newly created one. Check the error from btrfs_create_dio_extent() before replacing the map and drop the input extent map on failure. Fixes: 5f9a8a51d8b9 ("Btrfs: add semaphore to synchronize direct IO writes with fsync") CC: stable@vger.kernel.org Reviewed-by: Qu Wenruo Reviewed-by: Filipe Manana Signed-off-by: Shuangpeng Bai Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/direct-io.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/fs/btrfs/direct-io.c b/fs/btrfs/direct-io.c index b80dc45c3ff9..27d227f5bdc0 100644 --- a/fs/btrfs/direct-io.c +++ b/fs/btrfs/direct-io.c @@ -280,17 +280,24 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map, em2 = btrfs_create_dio_extent(BTRFS_I(inode), dio_data, start, &file_extent, type); btrfs_dec_nocow_writers(bg); - if (type == BTRFS_ORDERED_PREALLOC) { + if (IS_ERR(em2)) { + ret = PTR_ERR(em2); + btrfs_free_extent_map(em); + *map = NULL; + goto out; + } + + /* + * True NOCOW writes don't need to create a new extent map, + * while PREALLOC writes must replace the existing one. + */ + if (em2) { + ASSERT(type == BTRFS_ORDERED_PREALLOC); btrfs_free_extent_map(em); *map = em2; em = em2; } - if (IS_ERR(em2)) { - ret = PTR_ERR(em2); - goto out; - } - dio_data->nocow_done = true; } else { /* Our caller expects us to free the input extent map. */