From: Gerald Schaefer Date: Fri, 8 Apr 2016 11:23:52 +0000 (+0200) Subject: s390/dcssblk: fix possible deadlock in remove vs. per-device attributes X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=1378a683443753923eb22d01ce322e92a383ba8a;p=openwrt%2Fstaging%2Fblogic.git s390/dcssblk: fix possible deadlock in remove vs. per-device attributes dcssblk_remove_store() holds the dcssblk_devices_sem semaphore while calling device_unregister(), which in turn tries to acquire the kernfs kn->dev_map rwsem for the device sysfs subtree. The same rwsem is also acquired when using the per-device sysfs attributes in the device sub-tree, and the attribute handlers then also acquire the dcssblk_devices_sem. This can lead to a deadlock when removing a DCSS while concurrently reading from / writing to one of its sysfs attributes. The following lockdep warning hinted towards the issue (CPU0 = dcssblk_remove_store, CPU1 = dcssblk_shared_store): [ 76.496047] Possible unsafe locking scenario: [ 76.496054] CPU0 CPU1 [ 76.496059] ---- ---- [ 76.496087] lock(&dcssblk_devices_sem); [ 76.496090] lock(s_active#175); [ 76.496106] lock(&dcssblk_devices_sem); [ 76.496110] lock(s_active#175); [ 76.496115] *** DEADLOCK *** Fix this by releasing the dcssblk_devices_sem semaphore, which only protects internal DCSS data, before calling device_unregister(). Signed-off-by: Gerald Schaefer Signed-off-by: Martin Schwidefsky --- diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c index 1bce9cf51b1e..b83908670a9a 100644 --- a/drivers/s390/block/dcssblk.c +++ b/drivers/s390/block/dcssblk.c @@ -756,15 +756,16 @@ dcssblk_remove_store(struct device *dev, struct device_attribute *attr, const ch blk_cleanup_queue(dev_info->dcssblk_queue); dev_info->gd->queue = NULL; put_disk(dev_info->gd); - device_unregister(&dev_info->dev); /* unload all related segments */ list_for_each_entry(entry, &dev_info->seg_list, lh) segment_unload(entry->segment_name); - put_device(&dev_info->dev); up_write(&dcssblk_devices_sem); + device_unregister(&dev_info->dev); + put_device(&dev_info->dev); + rc = count; out_buf: kfree(local_buf);