Messages in this thread | | | Date | Wed, 23 Jan 2008 12:32:49 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts disabled |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > > On Wed, 23 Jan 2008, Daniel Walker wrote: > > > > > On Wed, 2008-01-23 at 11:02 -0500, Steven Rostedt wrote: > > > > > + if (!irqs_disabled() && wake_klogd) > > > wake_up_klogd(); > > > > This causes a regression .. When printk is called during an OOPS in > > kernels without this change then the OOPS will get logged, since the > > logging process (klogd) is woken to handle the messages.. If you apply > > this change klogd doesn't wakeup, and hence doesn't log the oops.. So if > > you remove the wakeup here you have to add it someplace else to maintain > > the logging .. > > > > (I'm not theorizing here, I have defects logged against this specific > > piece of code..) > > It wont get woken up anyway. Did you look at wake_up_klogd? > > void wake_up_klogd(void) > { > if (!oops_in_progress && waitqueue_active(&log_wait)) > wake_up_interruptible(&log_wait); > } > > > So if oops_in_progress is set, then it still wont get woken. Perhaps it > got woken some other way? Or is oops_in_progress not set in these oops? > > One other solution is to make the runqueue locks visible externally. Like: > > in sched.c: > > int runqueue_is_locked(void) > { > int cpu = get_cpu(); > struct rq *rq = cpu_rq(cpu); > int ret; > > ret = spin_is_locked(&rq->lock); > put_cpu(); > return ret; > } > > And in printk we could do: > > if (wake_klogd && !runqueue_is_locked()) > wake_up_klogd(); > > This probably is the cleanest solution since it simply prevents the > deadlock from occurring. >
FYI :
kernel/panic.c
NORET_TYPE void panic(const char * fmt, ...) { .... bust_spinlocks(1); ... bust_spinlocks(0); ...
In bust_spinlocks :
void __attribute__((weak)) bust_spinlocks(int yes) { if (yes) { ++oops_in_progress; } else { #ifdef CONFIG_VT unblank_screen(); #endif if (--oops_in_progress == 0) wake_up_klogd(); } }
Where the final wake_up happens while oops_in_progress is 0, but interrupts are still disabled.
So about my previous email, proposing testing oops_in_progress, it just won't work.
Mathieu
> -- Steve >
-- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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