Messages in this thread | | | Date | Wed, 16 Apr 2014 19:38:18 -0700 | From | Greg KH <> | Subject | Re: rb tree hrtimer lockup bug (found by perf_fuzzer) |
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On Thu, Apr 17, 2014 at 01:00:53AM +0200, Thomas Gleixner wrote: > On Sat, 5 Apr 2014, Greg KH wrote: > > On Mon, Mar 31, 2014 at 01:18:34PM +0200, Thomas Gleixner wrote: > > > On Thu, 27 Mar 2014, Vince Weaver wrote: > > > > On Wed, 26 Mar 2014, Thomas Gleixner wrote: > > > > > Ok. So we know now what we are looking for. > > > > > > > > > > [ 1.579996] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled > > > > > ÿ[ 1.607279] 00:09: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A > > > > > [ 1.615032] kobject: 'ttyS1' (ffff88011772ac10): kobject_release, parent (null) (delayed 250) > > > > > [ 1.624534] kobject: '(null)' (ffff8801177400f0): kobject_release, parent (null) (delayed 500) > > > > > [ 1.654213] 0000:00:16.3: ttyS1 at I/O 0xf0e0 (irq = 19, base_baud = 115200) is a 16550A > > > > > > > > > > [ 3.294047] Invalid timer base: tmr ffff880117740150 tmr->base (null) base ffff880118898000 > > > > > > > > > > 1634110us : obj: ffff880117740130 initialized kobject_delayed_cleanup+0x0/0x90 > > > > > > > > > > So that happens in the context of the 8250 serial driver. > > > > > > > > > > ... > > > > > > > > > > Below is a patch which gives us the call path of the unnamed object > > > > > which causes the crash. > > > > > > > > I've attached the boot log with that patch applied. > > > > > > Vince, can you please disable CONFIG_DEBUG_KOBJECT_RELEASE and remove > > > all the debug patches to see whether the issue goes away? > > > > > > I had a deeper look down that code path and the issue is, that the > > > serial core is not compatible with the deferred kobject release. > > > > > > The tty_io layer uses a kobject embedded in its internal tty device > > > representation and reuses that. > > > > It does? What kobject is that? I've dug through the code and I can't > > find it. I see where we create a new device in > > tty_register_device_attr() which is dynamic and should be torn down when > > free_tty_struct() is called eventually. > > It's not about the dynamic stuff. > > > > So it seems that for whatever reason the tty layer releases ttyS1 and > > > then initializes it again. So the deferred release will queue the > > > object for release while the tty layer happily reinitializes it. > > > > That's not good, but I can't find that code path, any hints? > > static int tty_cdev_add(struct tty_driver *driver, dev_t dev, > unsigned int index, unsigned int count) > { > /* init here, since reused cdevs cause crashes */ > cdev_init(&driver->cdevs[index], &tty_fops); > > The comment is interesting ... > > And cdevs is an array of struct cdev: > > struct cdev { > struct kobject kobj;
Those are not "real" kobjects, and are never registered with the kobject core.
I really need to go rename those one of these days, and just make them a separate object, as they have nothing to do with a "normal" kobject other than the reference count and the use of the kobject map stuff.
So if this is showing up as a problem, something else is going on here, as this should not be an issue at all.
thanks,
greg k-h -- 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/
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