diff options
authorLin Feng <>2021-11-12 13:36:29 +0800
committerJens Axboe <>2021-12-14 20:32:54 -0700
commitaa97f6cdb7e92909e17c8ca63e622fcb81d57a57 (patch)
parentcb2ac2912a9ca7d3d26291c511939a41361d2d83 (diff)
bcache: fix NULL pointer reference in cached_dev_detach_finishblock-5.16-2021-12-17
Commit 0259d4498ba4 ("bcache: move calc_cached_dev_sectors to proper place on backing device detach") tries to fix calc_cached_dev_sectors when bcache device detaches, but now we have: cached_dev_detach_finish ... bcache_device_detach(&dc->disk); ... closure_put(&d->c->caching); d->c = NULL; [*explicitly set dc->disk.c to NULL*] list_move(&dc->list, &uncached_devices); calc_cached_dev_sectors(dc->disk.c); [*passing a NULL pointer*] ... Upper codeflows shows how bug happens, this patch fix the problem by caching dc->disk.c beforehand, and cache_set won't be freed under us because c->caching closure at least holds a reference count and closure callback __cache_set_unregister only being called by bch_cache_set_stop which using closure_queue(&c->caching), that means c->caching closure callback for destroying cache_set won't be trigger by previous closure_put(&d->c->caching). So at this stage(while cached_dev_detach_finish is calling) it's safe to access cache_set dc->disk.c. Fixes: 0259d4498ba4 ("bcache: move calc_cached_dev_sectors to proper place on backing device detach") Signed-off-by: Lin Feng <> Signed-off-by: Coly Li <> Link: Signed-off-by: Jens Axboe <>
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 86b9e355c583..140f35dc0c45 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1139,6 +1139,7 @@ static void cancel_writeback_rate_update_dwork(struct cached_dev *dc)
static void cached_dev_detach_finish(struct work_struct *w)
struct cached_dev *dc = container_of(w, struct cached_dev, detach);
+ struct cache_set *c = dc->disk.c;
BUG_ON(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags));
@@ -1156,7 +1157,7 @@ static void cached_dev_detach_finish(struct work_struct *w)
list_move(&dc->list, &uncached_devices);
- calc_cached_dev_sectors(dc->disk.c);
+ calc_cached_dev_sectors(c);
clear_bit(BCACHE_DEV_DETACHING, &dc->disk.flags);
clear_bit(BCACHE_DEV_UNLINK_DONE, &dc->disk.flags);