4.16-stable review patch. If anyone has any objections, please let me know.
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From: Omar Sandoval osandov@fb.com
commit d50147381aa0c9725d63a677c138c47f55d6d3bc upstream.
Jun Wu at Facebook reported that an internal service was seeing a return value of 1 from ftruncate() on Btrfs in some cases. This is coming from the NEED_TRUNCATE_BLOCK return value from btrfs_truncate_inode_items().
btrfs_truncate() uses two variables for error handling, ret and err. When btrfs_truncate_inode_items() returns non-zero, we set err to the return value. However, NEED_TRUNCATE_BLOCK is not an error. Make sure we only set err if ret is an error (i.e., negative).
To reproduce the issue: mount a filesystem with -o compress-force=zstd and the following program will encounter return value of 1 from ftruncate:
int main(void) { char buf[256] = { 0 }; int ret; int fd;
fd = open("test", O_CREAT | O_WRONLY | O_TRUNC, 0666); if (fd == -1) { perror("open"); return EXIT_FAILURE; }
if (write(fd, buf, sizeof(buf)) != sizeof(buf)) { perror("write"); close(fd); return EXIT_FAILURE; }
if (fsync(fd) == -1) { perror("fsync"); close(fd); return EXIT_FAILURE; }
ret = ftruncate(fd, 128); if (ret) { printf("ftruncate() returned %d\n", ret); close(fd); return EXIT_FAILURE; }
close(fd); return EXIT_SUCCESS; }
Fixes: ddfae63cc8e0 ("btrfs: move btrfs_truncate_block out of trans handle") CC: stable@vger.kernel.org # 4.15+ Reported-by: Jun Wu quark@fb.com Signed-off-by: Omar Sandoval osandov@fb.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/inode.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -9238,7 +9238,8 @@ static int btrfs_truncate(struct inode * BTRFS_EXTENT_DATA_KEY); trans->block_rsv = &fs_info->trans_block_rsv; if (ret != -ENOSPC && ret != -EAGAIN) { - err = ret; + if (ret < 0) + err = ret; break; }