Messages in this thread | | | Date | Wed, 07 Apr 2004 09:00:14 -0500 | From | Brian King <> | Subject | Re: call_usermodehelper hang |
| |
Greg KH wrote: > On Tue, Apr 06, 2004 at 05:29:03PM -0700, Andrew Morton wrote: > >>Brian King <brking@us.ibm.com> wrote: >> >>>I have been running into some kernel hangs due to call_usermodehelper. Looking >>>at the backtrace, it looks to me like there are deadlock issues with adding >>>devices from work queues. Attached is a sample backtrace from one of the >>>hangs I experienced. My question is why does call_usermodehelper do 2 different >>>things depending on whether or not it is called from the kevent task? It appears >>>that the simple way to fix the hang would be to never have call_usermodehelper >>>use a work_queue since it must be called from process context anyway, or >>>am I missing something? >>> >> >>swapper is running call_usermodehelper() while holding >>down_write(&bus->subsys.rwsem); via bus_add_driver(). >> >>Meanwhile, keventd is blocked on the same lock in bus_add_device(). >> >>I'd say that the bug lies in the kobject code - we should not call >>call_usermodehelper() while holding any locks which keventd may ever >>acquire. > > > How is keventd calling sysfs code? Is scsi using it to drive device > detection somehow? I don't see how the kobject core code itself can do > this on its own.
scsi_add_device is being called from keventd by the ipr LLD. I am assuming this is a reasonable thing to do. If not, then I would argue the scsi_add_device API is broken as it must be called from task level, and if a LLD cannot use keventd, then every LLD that wants to use it would need to create its own workqueue thread.
-- Brian King eServer Storage I/O IBM Linux Technology Center
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |