lkml.org 
[lkml]   [2022]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v5] devcoredump : Serialize devcd_del work
On Fri, May 27, 2022 at 07:33:40PM +0530, Mukesh Ojha wrote:
> In following scenario(diagram), when one thread X running dev_coredumpm()
> adds devcd device to the framework which sends uevent notification to
> userspace and another thread Y reads this uevent and call to
> devcd_data_write() which eventually try to delete the queued timer that
> is not initialized/queued yet.
>
> So, debug object reports some warning and in the meantime, timer is
> initialized and queued from X path. and from Y path, it gets reinitialized
> again and timer->entry.pprev=NULL and try_to_grab_pending() stucks.
>
> To fix this, introduce mutex and a boolean flag to serialize the behaviour.
>
> cpu0(X) cpu1(Y)
>
> dev_coredump() uevent sent to user space
> device_add() ======================> user space process Y 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()
> timer_fixup_assert_init()
> timer_setup()
> do_init_timer()
> /*
> Above call reinitializes
> the timer to
> timer->entry.pprev=NULL
> and this will be checked
> later in timer_pending() call.
> */
> timer_pending()
> !hlist_unhashed_lockless(&timer->entry)
> !h->pprev
> /*
> del_timer() checks h->pprev and finds
> it to be NULL due to which
> try_to_grab_pending() stucks.
> */
>
> Link: https://lore.kernel.org/lkml/2e1f81e2-428c-f11f-ce92-eb11048cb271@quicinc.com/
> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> ---

I need an ack from the devcoredump maintainer before I can take this...

thanks,

greg k-h

\
 
 \ /
  Last update: 2022-06-27 15:14    [W:0.076 / U:0.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site