block: free copied pages when blk_rq_map_kern() fails

block: free copied pages when blk_rq_map_kern() fails

bio_copy_kern() allocates pages that are normally freed by the bio
completion callback. If blk_rq_append_bio() rejects the bio, however,
blk_rq_map_kern() only drops the bio reference. Since bio_put() does not
free pages referenced by the bio vectors, those pages leak.

This can happen when the bio exceeds the queue segment constraints or
when a later mapping cannot be merged into a request built by earlier
calls. Track whether the buffer was copied and free those pages before
dropping the rejected bio.

Fixes: 3a5a39276d2a ("block: allow blk_rq_map_kern to append to requests")
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260715073518.96042-1-liu.yun@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>