Messages in this thread Patch in this message | | | Date | Wed, 5 Oct 2005 16:41:27 +0200 | From | Ingo Molnar <> | Subject | Re: 2.6.14-rc3-rt2 |
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* Steven Rostedt <rostedt@goodmis.org> wrote:
> Hi Ingo, > > I just notice that I get the following output: > > BUG: gdm:4351 task might have lost a preemption check! > [<c010433f>] dump_stack+0x1f/0x30 (20) > [<c011c06f>] preempt_enable_no_resched+0x5f/0x70 (20) > [<c011b6c9>] sys_sched_yield+0x69/0xb0 (24) > [<c01033d6>] syscall_call+0x7/0xb (-8116) > --------------------------- > | preempt count: 00000000 ] > | 0-level deep critical section nesting: > ---------------------------------------- > > ------------------------------ > | showing all locks held by: | (gdm/4351 [dbb727a0, 118]): > ------------------------------ > > > I looked at this a little and the offending code is here in > sys_sched_yield: > > /* > * Since we are going to call schedule() anyway, there's > * no need to preempt or enable interrupts: > */ > spin_unlock_no_resched(&rq->lock); > > __schedule(); > > So what's the reason for the message? Is it to detect when a > preemption count goes to zero and isn't rescheduled? At least in this > part of the kernel it's ok because it is just about to call schedule. > So is there some way to flag this call to not produce the message? > Since the message is only outputed once, it seems useless if it only > gets outputted on a false positive.
the patch below should solve this. I've added the warning to preempt_enable_no_resched() because we had bugs in this area, and i wanted to have a chance to review all 'potentially problematic' places. So i'm changing them to __preempt_enable_no_resched() when they turn out to be safe. (In the future we'll likely remove the debugging message and get rid of __preempt_enable_no_resched().)
Ingo
Index: linux/include/linux/spinlock_api_up.h =================================================================== --- linux.orig/include/linux/spinlock_api_up.h +++ linux/include/linux/spinlock_api_up.h @@ -45,7 +45,7 @@ do { preempt_enable(); __release(lock); (void)(lock); } while (0) #define __UNLOCK_NO_RESCHED(lock) \ - do { preempt_enable_no_resched(); __release(lock); (void)(lock); } while (0) + do { __preempt_enable_no_resched(); __release(lock); (void)(lock); } while (0) #define __UNLOCK_BH(lock) \ do { preempt_enable_no_resched(); local_bh_enable(); __release(lock); (void)(lock); } while (0) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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