Messages in this thread | | | Date | Wed, 13 Apr 2022 15:01:34 +0200 | From | Greg KH <> | Subject | Re: Possible race in dev_coredumpm()-del_timer() path |
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On Wed, Apr 13, 2022 at 04:51:18PM +0530, Mukesh Ojha wrote: > > > On 4/13/2022 4:28 PM, Greg KH wrote: > > On Wed, Apr 13, 2022 at 03:46:39PM +0530, Mukesh Ojha wrote: > > > On Wed, Apr 13, 2022 at 07:34:24AM +0200, Greg KH wrote: > > > > On Wed, Apr 13, 2022 at 10:59:22AM +0530, Mukesh Ojha wrote: > > > > > Hi All, > > > > > > > > > > We are hitting one race due to which try_to_grab_pending() is stuck . > > > > > > > > What kernel version are you using? > > > > > > 5.10 > > > > 5.10.0 was released a very long time ago. Please use a more modern > > kernel release :) > > > > > Sorry, for the formatting mess. > > > > > > > > In following scenario, while running (p1)dev_coredumpm() devcd device is > > > > > added to > > > > > the framework and uevent notification sent to userspace that result in the > > > > > call to (p2) devcd_data_write() > > > > > which eventually try to delete the queued timer which in the racy scenario > > > > > timer is not queued yet. > > > > > So, debug object report some warning and in the meantime timer is > > > > > initialized and queued from p1 path. > > > > > and from p2 path it gets overriden again timer->entry.pprev=NULL and > > > > > try_to_grab_pending() stuck > > > 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? > > There is no issue if we disable debug object. > Here, some client module try to collect dump > via dev_coredumpm() which creates devcdX device and > expects userspace to read this data. Here, it might be > exposing a synchronization issue between dev_coredumpm() > and devcd_data_write() perhaps, a mutex ??
Any reason you did not answer any of the questions I asked?
{sigh}
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