From: Gerald Schaefer Date: Tue, 22 Aug 2023 15:19:32 +0000 (+0200) Subject: s390/dcssblk: fix lockdep warning X-Git-Tag: v6.6.17~3973^2~13 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=789dd8cb1eb1503c8167bf2ffc88f74a70245044;p=platform%2Fkernel%2Flinux-rpi.git s390/dcssblk: fix lockdep warning dcssblk_remove_store() holds the dcssblk_devices_sem semaphore while calling del_gendisk(dev_info->gd), which in turn tries to acquire disk->open_mutex. Then there is dcssblk_release(), which is called with disk->open_mutex held, and tries to acquire dcssblk_devices_sem. Lockdep reports this as possible circular locking dependency (CPU0 = dcssblk_remove_store, CPU1 = dcssblk_release): [ 44.948865] Possible unsafe locking scenario: [ 44.948866] CPU0 CPU1 [ 44.948867] ---- ---- [ 44.948868] lock(&dcssblk_devices_sem); [ 44.948870] lock(&disk->open_mutex); [ 44.948872] lock(&dcssblk_devices_sem); [ 44.948874] lock(&disk->open_mutex); [ 44.948876] *** DEADLOCK *** In practice, this deadlock should not happen, since dcssblk_remove_store() checks for dev_info->use_count != 0 after acquiring dcssblk_devices_sem, and breaks out before calling del_gendisk(). dev_info->use_count will be decremented in dcssblk_release(), protected by dcssblk_devices_sem. Still there is no need for dcssblk_remove_store() to hold the dcssblk_devices_sem until after calling del_gendisk(), as this only protects dcssblk internal data. So fix the lockdep warning by releasing dcssblk_devices_sem earlier. Also move the segment_unload() loop up, similar to dcssblk_shared_store() error path, no need to do that after calling del_gendisk(). Also change dcssblk_shared_store() error path, where dcssblk_devices_sem was also released only after calling del_gendisk(), and a similar lockdep warning could be triggered (but also deadlock prevented by check for dev_info->use_count). Acked-by: Heiko Carstens Signed-off-by: Gerald Schaefer Signed-off-by: Heiko Carstens --- diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c index 06bcb6c..4b7ecd4 100644 --- a/drivers/s390/block/dcssblk.c +++ b/drivers/s390/block/dcssblk.c @@ -411,13 +411,13 @@ removeseg: segment_unload(entry->segment_name); } list_del(&dev_info->lh); + up_write(&dcssblk_devices_sem); dax_remove_host(dev_info->gd); kill_dax(dev_info->dax_dev); put_dax(dev_info->dax_dev); del_gendisk(dev_info->gd); put_disk(dev_info->gd); - up_write(&dcssblk_devices_sem); if (device_remove_file_self(dev, attr)) { device_unregister(dev); @@ -790,18 +790,17 @@ dcssblk_remove_store(struct device *dev, struct device_attribute *attr, const ch } list_del(&dev_info->lh); + /* unload all related segments */ + list_for_each_entry(entry, &dev_info->seg_list, lh) + segment_unload(entry->segment_name); + up_write(&dcssblk_devices_sem); + dax_remove_host(dev_info->gd); kill_dax(dev_info->dax_dev); put_dax(dev_info->dax_dev); del_gendisk(dev_info->gd); put_disk(dev_info->gd); - /* unload all related segments */ - list_for_each_entry(entry, &dev_info->seg_list, lh) - segment_unload(entry->segment_name); - - up_write(&dcssblk_devices_sem); - device_unregister(&dev_info->dev); put_device(&dev_info->dev);