You are right !! It is not a right solution . It is a speculation where the panic was.
[38261.652100] Call trace: [38261.654616] [<ffffffc000aa6fe0>] mm_update_next_owner+0x190/0x238 [38261.660766] [<ffffffc000aa728c>] do_exit+0x204/0x924 [38261.665790] [<ffffffc000aa7a1c>] do_group_exit+0x40/0xcc [38261.671169] [<ffffffc000ab59cc>] get_signal_to_deliver+0x218/0x57c [38261.677409] [<ffffffc000a87e6c>] do_signal+0x534/0x550 [38261.682608] [<ffffffc000a88070>] do_notify_resume+0x20/0x58 -----Original Message----- From: Oleg Nesterov [mailto:[email protected]] Sent: Wednesday, April 16, 2014 9:58 PM To: Peter Chiang Cc: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] Subject: Re: [PATCH] mm : Avoid candidate task is equal to current task On 04/16, Peter Chiang wrote: > > mm_update_next_owner() call from exit_mm() , and exit_mm() change > tsk->mm to NULL If p==c , It seems to be impossible that mm == c->mm > (tsk->mm) . > Because mm is non-NULL and c->mm is NULL . Confused, please see below. > Fix kernel panic when finding a new owner for the mm and the new owner > is equal to current onwer Did you actually observe the panic ? > diff --git a/kernel/exit.c b/kernel/exit.c index 6ed6a1d..aa98422 > 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -399,7 +399,7 @@ retry: > * here often > */ > do_each_thread(g, c) { > - if (c->mm == mm) > + if ((c != p) && (c->mm == mm)) > goto assign_new_owner; > } while_each_thread(g, c); p == current. This is always called with p->mm == NULL and mm != NULL. So, if c->mm == mm then at least c->mm != NULL, and this means that c == p is not possible? And it seems that this is exactly what you meant above. So why do you think we need this change? Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
