[bug report] dm cache: fix write hang in passthrough mode

[Dan Carpenter <error27@gmail.com>]

Hello Ming-Hung Tsai,

Commit 4ca8b8bd952d ("dm cache: fix write hang in passthrough mode")
from Feb 9, 2026 (linux-next), leads to the following Smatch static
checker warning:

	drivers/md/dm-cache-target.c:1527 invalidate_committed()
	error: dereferencing freed memory 'mg' (line 1525)

drivers/md/dm-cache-target.c
    1517 static void invalidate_committed(struct work_struct *ws)
    1518 {
    1519         struct dm_cache_migration *mg = ws_to_mg(ws);
    1520         struct cache *cache = mg->cache;
    1521         struct bio *bio = mg->overwrite_bio;
    1522         struct per_bio_data *pb = get_per_bio_data(bio);
    1523 
    1524         if (mg->k.input)
    1525                 invalidate_complete(mg, false);
                                             ^^
This frees mg.

    1526 
--> 1527         init_continuation(&mg->k, invalidate_completed);
                                    ^^
    1528         remap_to_origin_clear_discard(cache, bio, mg->invalidate_oblock);
                                                           ^^
    1529         dm_hook_bio(&pb->hook_info, bio, overwrite_endio, mg);
                                                                   ^^
But we still dereference it later.

    1530         dm_submit_bio_remap(bio, NULL);
    1531 }

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regards,
dan carpenter