On Fri 2018-11-23 11:40:48, Sergey Senozhatsky wrote: > On (11/22/18 11:16), Peter Zijlstra wrote: > > > So maybe we need to switch debug objects print-outs to _always_ > > > printk_deferred(). Debug objects can be used in code which cannot > > > do direct printk() - timekeeping is just one example. > > > > No, printk_deferred() is a disease, it needs to be eradicated, not > > spread around. > > deadlock-free printk() is deferred, but OK.
The best solution would be lockless console drivers. Sigh. > Another idea then: > > --- > > diff --git a/lib/debugobjects.c b/lib/debugobjects.c > index 70935ed91125..3928c2b2f77c 100644 > --- a/lib/debugobjects.c > +++ b/lib/debugobjects.c > @@ -323,10 +323,13 @@ static void debug_print_object(struct debug_obj *obj, > char *msg) > void *hint = descr->debug_hint ? > descr->debug_hint(obj->object) : NULL; > limit++; > + > + bust_spinlocks(1); > WARN(1, KERN_ERR "ODEBUG: %s %s (active state %u) " > "object type: %s hint: %pS\n", > msg, obj_states[obj->state], obj->astate, > descr->name, hint); > + bust_spinlocks(0); > } > debug_objects_warnings++; > } > > --- > > This should make serial consoles re-entrant. > So printk->console_driver_write() hopefully will not deadlock. Is the re-entrance safe? Some risk might be acceptable in Oops/panic situations. It is much less acceptable for random warnings. Best Regards, Petr _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
