Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: Possible race in dev_coredumpm()-del_timer() path | Date | Thu, 14 Apr 2022 12:38:13 +0200 |
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On Wed, Apr 13 2022 at 12:58, Greg KH wrote: > On Wed, Apr 13, 2022 at 03:46:39PM +0530, Mukesh Ojha wrote: >> p1 p2(X) >> >> dev_coredump() uevent sent to userspace >> device_add() =========================> userspace process X reads the uevents >> writes to devcd fd which >> results into writes to >> >> devcd_data_write() >> mod_delayed_work() >> try_to_grab_pending() >> del_timer() >> debug_assert_init() >> INIT_DELAYED_WORK >> schedule_delayed_work >> debug_object_fixup() > > Why do you have object debugging enabled? That's going to take a LONG > time, and will find bugs in your code. Perhaps like this one?
It's not finding bugs in his code. It finds bug in the upstream dev_coredump code.
> And if you turn object debugging off, what happens?
The debugobject splat goes away, but the problem persists.
device_add() -> uevent
Preemption or concurrency:
devcd_data_write() mod_delayed_work(..., w, 0); <- Uninitialized.
The dev_coredump code exposes the device before it is fully initialized and a write ending up in devcd_data_write() touches uninitialized work.
It does not help to move the initialization before device_add() as that creates another problem:
INIT_DELAYED_WORK(w) ... device_add() -> uevent
Preemption or concurrency:
devcd_data_write() mod_delayed_work(..., w, 0); <- Schedules work immediately
work_queue_runs() devcd_del(w) device_del() put_device() <- Drops the last reference
initialization continues...
So, yes this needs serialization of some sort.
Same problem vs. disabled_store().
Thanks,
tglx
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