blk-iocost: abort weight transfer on invalid donation weights

transfer_surpluses() warns and then keeps going when the donation
calculation produced invalid weights.  The following propagation can then
divide by a zero hweight_inuse, so the warning is immediately followed by a
divide error.

When the check trips, abandon this period's donation transfer and release
the walk lists.  This trades one period without donation for not crashing;
the invalid state is not expected on the normal path.

Developed with assistance from Claude Code (Anthropic): the assistant
analysed the failure path, drafted the change and ran the checks listed
below.  The author reviewed the result and remains responsible for it.

Fixes: e08d02aa5fc9 ("blk-iocost: implement Andy's method for donation weight updates")
Cc: stable@vger.kernel.org
Signed-off-by: Kunhai Dai <daikunhai@didiglobal.com>
Tested-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Tao Cui <cuitao@kylinos.cn>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://patch.msgid.link/20261019125412.3123895-2-daikunhai@didiglobal.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions