> >> However, I've found one more race condition leading to a crash when > >> tracing is enabled, this time from the writeback:queue trace point from > >> bdi_queue_work(). The cause is the same, i.e. bdi->dev is NULL. This > >> was produced with the help of the following delay patch. trace+log is > >> attached. > > > > Rabin, this should fix the bug. Note that I take no efforts to remove > > the to-be-queued and already-queued works. I'm also a bit afraid if > > the traces in the balance_dirty_pages() path (trace_balance_dirty_pages, > > trace_bdi_dirty_ratelimit and writeback_wake_background) will have > > similar NULL dereference bug. Do you test it by physically hot > > removing a SD card, or with some detach command or emulation? > > > > Thanks, > > Fengguang > > Hi. Wu. > I can reproduce this problem too. And I know this problem is fixed > with your patch. > Thanks. > Tested-by: Namjae Jeon <linkinjeon@xxxxxxxxx> Namjae, thank you for the testing! FYI I've pushed it to linux-next. Thanks, Fengguang > > > > --- > > Subject: writeback: fix dereferencing NULL bdi->dev on trace_writeback_queue > > Date: Sat Feb 04 20:54:03 CST 2012 > > > > When the SD card is hot removed without umount, del_gendisk() will call > > bdi_unregister() but not destroy/free it. This leaves the bdi in the > > bdi->dev = NULL, bdi->wb.task = NULL, bdi->bdi_list removed state. > > > > If someone 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 <rabin@xxxxxx> > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > --- > > include/trace/events/writeback.h | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > --- linux-next.orig/include/trace/events/writeback.h 2012-02-04 20:51:01.000000000 +0800 > > +++ linux-next/include/trace/events/writeback.h 2012-02-04 20:54:00.000000000 +0800 > > @@ -47,7 +47,10 @@ DECLARE_EVENT_CLASS(writeback_work_class > > __field(int, reason) > > ), > > 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; > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
