Messages in this thread | | | Subject | oprofile can cause an NMI to schedule (was: [RT] scheduling and oprofile) | From | Steven Rostedt <> | Date | Mon, 23 Oct 2006 22:24:34 -0400 |
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On Mon, 2006-10-23 at 14:23 -0700, Mike Kravetz wrote: > I've been trying to use oprofile on an RT kernel to look at some > performance issues. While running I notice the following sent to > the console: > > BUG: scheduling with irqs disabled: java/0x00000000/4521 > caller is rt_mutex_slowlock+0x156/0x1dd > [<c032051a>] schedule+0x65/0xd2 (8) > [<c0321338>] rt_mutex_slowlock+0x156/0x1dd (12) > [<c032142a>] rt_mutex_lock+0x24/0x28 (72) > [<c0134904>] rt_down_read+0x38/0x3b (20) > [<c0322a89>] do_page_fault+0xe3/0x52d (12) > [<c03229a6>] do_page_fault+0x0/0x52d (76) > [<c01033bb>] error_code+0x4f/0x54 (8) > [<c01ce6d0>] __copy_from_user_ll+0x55/0x7c (44) > [<f89be7ef>] dump_user_backtrace+0x2e/0x56 [oprofile] (24) > [<c0134869>] rt_up_read+0x3e/0x41 (20) > [<f89be864>] x86_backtrace+0x4a/0x5a [oprofile] (20) > [<f89bd53a>] oprofile_add_sample+0x73/0x89 [oprofile] (20) > [<f89beea3>] athlon_check_ctrs+0x22/0x4a [oprofile] (32) > [<f89be8c5>] nmi_callback+0x18/0x1b [oprofile] (28) > [<c01041ff>] do_nmi+0x24/0x33 (12) > [<c0103462>] nmi_stack_correct+0x1d/0x22 (16) > > It seems strange to me that oprofile would be calling > '__copy_from_user_ll' in this context. I can see why the > changes made for RT locking expose this. But, doesn't this > issue also exist on non-RT (default) kernels? What happens > when we generate a page fault in this context on non-RT kernels? >
As Mike has pointed out here, oprofile _can_ cause the nmi to schedule. Here's the path: (looking at vanilla 2.6.18).
arch/i386/oprofile/nmi_int.c: nmi_callback
return model->check_ctrs(regs, &cpu_msrs[cpu]);
if model == &op_athlon_spec (could be a problem with others, but I'm only looking here).
op_athlon_spec.check_ctrs = &athlon_check_ctrs
Here's the calling path:
athlon_check_ctrs
==> oprofile_add_sample
==> oprofile_add_ext_sample
==> oprofile_ops.backtrace == x86_backtrace
==> dump_user_backtrace
==> __copy_from_user_inatomic
Don't let the name fool you, this _can_ schedule! (and says so in the comments above it).
Now perhaps on a vanilla kernel opfile_add_ext_sample is not likely to have log_sample fail. I don't know, but this path exits, so we can indeed schedule in a NMI interrupt.
Mike, thanks for pointing this out.
-- Steve
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