From: Lin Feng linf@wangsu.com
mainline inclusion from v5.16-rc6 commit aa97f6cdb7e92909e17c8ca63e622fcb81d57a57 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I59A5L?from=project-issue CVE: N/A
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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 linf@wangsu.com Signed-off-by: Coly Li colyli@suse.de Link: https://lore.kernel.org/r/20211112053629.3437-2-colyli@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- drivers/md/bcache/super.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 203f85599018..a98b46d3cd0b 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1150,6 +1150,7 @@ 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)); BUG_ON(refcount_read(&dc->count)); @@ -1167,7 +1168,7 @@ static void cached_dev_detach_finish(struct work_struct *w)
bcache_device_detach(&dc->disk); 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);