From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120217005511.008575233@linuxfoundation.org> Date: Thu, 16 Feb 2012 16:55:17 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Rabin Vincent , Namjae Jeon , Wu Fengguang Subject: [08/15] writeback: fix dereferencing NULL bdi->dev on trace_writeback_queue In-Reply-To: <20120217005650.GA17119@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Wu Fengguang commit 977b7e3a52a7421ad33a393a38ece59f3d41c2fa upstream. When a SD card is hot removed without umount, del_gendisk() will call bdi_unregister() without destroying/freeing it. This leaves the bdi in the bdi->dev = NULL, bdi->wb.task = NULL, bdi->bdi_list removed state. When sync(2) gets the bdi before bdi_unregister() and calls bdi_queue_work() after the unregister, trace_writeback_queue will be dereferencing the NULL bdi->dev. Fix it with a simple test for NULL. LKML-reference: http://lkml.org/lkml/2012/1/18/346 Reported-by: Rabin Vincent Tested-by: Namjae Jeon Signed-off-by: Wu Fengguang Signed-off-by: Greg Kroah-Hartman --- include/trace/events/writeback.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -23,7 +23,10 @@ DECLARE_EVENT_CLASS(writeback_work_class __field(int, for_background) ), TP_fast_assign( - strncpy(__entry->name, dev_name(bdi->dev), 32); + struct device *dev = bdi->dev; + if (!dev) + dev = default_backing_dev_info.dev; + strncpy(__entry->name, dev_name(dev), 32); __entry->nr_pages = work->nr_pages; __entry->sb_dev = work->sb ? work->sb->s_dev : 0; __entry->sync_mode = work->sync_mode;