[PATCH] btrfs: fix extent changeset leak in encoded writes

[Breno Leitao <leitao@debian.org>]

Investigating some machines with kmemleak, I am constantly seeing
the following memory leak that seems real.

  kmemleak: unreferenced object 0xffff88869f7d01c0 (size 64):
  kmemleak:   comm "btrfs", pid 1613416, jiffies 4316358595
  kmemleak:   backtrace (crc ab59040a):
  kmemleak:     __kmalloc_cache_noprof
  kmemleak:     qgroup_reserve_data
  kmemleak:     btrfs_qgroup_reserve_data
  kmemleak:     btrfs_do_encoded_write
  kmemleak:     btrfs_do_write_iter
  kmemleak:     btrfs_ioctl_encoded_write
  kmemleak:     btrfs_ioctl
  kmemleak:   ... and 2 more object(s) with the same backtrace

and

  kmemleak: unreferenced object 0xffff88830d94edc0 (size 64):
  kmemleak:   comm "btrfs", pid 1613416, jiffies 4316358595
<snip>
  kmemleak:   ... and 2 more object(s) with the same backtrace

Looking at the code, it seems we don't free data_reserved, but
we should (!?). I was able to come up with a xfstest test that exposes
the kmemleak above:

https://github.com/leitao/xfstest/commit/81c83a3fbb20b4ad695055ede7fcb73d3ffa2e52

Free the changeset on the way out, as every other caller of
btrfs_qgroup_reserve_data() already does.

Fixes: 7c0c7269f7b5 ("btrfs: add BTRFS_IOC_ENCODED_WRITE")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 fs/btrfs/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 0fcbfc3939462..f8ad96256ff67 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9965,6 +9965,7 @@ ssize_t btrfs_do_encoded_write(struct kiocb *iocb, struct iov_iter *from,
 	if (cb)
 		cleanup_compressed_bio(cb);
 out:
+	extent_changeset_free(data_reserved);
 	if (ret >= 0)
 		iocb->ki_pos += encoded->len;
 	return ret;

---
base-commit: 95d6a9ccef99117115e41e9adb271243bd5e985b
change-id: 20260731-btrfs_kmemleak-d44637bd2518

Best regards,
--  
Breno Leitao <leitao@debian.org>