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Date: Wed, 7 Jan 2009 19:30:27 +0300 From: "Alexey Zaytsev" <alexey.zaytsev@...il.com> To: LKML <linux-kernel@...r.kernel.org> Cc: "Ingo Molnar" <mingo@...e.hu>, "Nick Piggin" <nickpiggin@...oo.com.au>, "Linus Torvalds" <torvalds@...ux-foundation.org> Subject: Re: linux-next: Tree for December 11 On Sun, Dec 14, 2008 at 17:34, Alexey Zaytsev <alexey.zaytsev@...il.com> wrote: > On Thu, Dec 11, 2008 at 15:40, Alexey Zaytsev <alexey.zaytsev@...il.com> wrote: >> On Thu, Dec 11, 2008 at 12:04, Stephen Rothwell <sfr@...b.auug.org.au> wrote: >>> Hi all, >>> >>> >>> ---------------------------------------------------------------------------- >> >> Hi. Almost a month later, the warning is still there, and now also in Linus' git. Am I the only one who sees it? [ 0.004000] Intel machine check reporting enabled on CPU#0. [ 0.004000] using mwait in idle threads. [ 0.004000] Checking 'hlt' instruction... <4>------------[ cut here ]------------ [ 0.004150] WARNING: at kernel/sched.c:4435 sub_preempt_count+0xae/0xc0() [ 0.004247] Hardware name: HP Compaq nx7300 (GB848ES#ACB) [ 0.004342] Modules linked in: [ 0.004477] Pid: 0, comm: swapper Not tainted 2.6.28-06859-gede6f5a #179 [ 0.004575] Call Trace: [ 0.004672] [<c012fbe6>] warn_slowpath+0x86/0xa0 [ 0.004770] [<c014e99b>] ? tick_check_oneshot_change+0x4b/0x100 [ 0.004868] [<c046dc00>] ? _spin_unlock_irq+0x10/0x30 [ 0.004963] [<c047045e>] sub_preempt_count+0xae/0xc0 [ 0.005060] [<c0134787>] _local_bh_enable+0x27/0xa0 [ 0.005155] [<c0134ac7>] __do_softirq+0xf7/0x150 [ 0.005250] [<c01349d0>] ? __do_softirq+0x0/0x150 [ 0.005345] <IRQ> [<c014ec2e>] ? tick_nohz_update_jiffies+0xe/0x50 [ 0.005488] [<c013494f>] ? irq_exit+0x7f/0x90 [ 0.005584] [<c0104f23>] ? do_IRQ+0xa3/0x120 [ 0.005678] [<c01038a7>] ? common_interrupt+0x27/0x2c [ 0.005773] [<c013007b>] ? try_acquire_console_sem+0x1b/0x30 [ 0.005872] [<c05f7378>] ? check_bugs+0xb8/0xe0 [ 0.005967] [<c05ef98a>] ? start_kernel+0x25a/0x2f0 [ 0.006062] [<c05ef270>] ? unknown_bootoption+0x0/0x210 [ 0.006159] [<c05ef07c>] ? __init_begin+0x7c/0xb0 [ 0.006260] ---[ end trace 4eaa2a86a8e2da22 ]--- [ 0.016003] OK. [ 0.016538] ACPI: Core revision 20080926 >> >> I'm seeing this warning early in boot logs. It does not appear on 2.6.28-rc7. >> Not sure how long it's been around. Haven't built -next for some time. >> >> [ 0.004000] Intel machine check reporting enabled on CPU#0. >> [ 0.004000] using mwait in idle threads. >> [ 0.004000] Checking 'hlt' instruction... <4>------------[ cut here >> ]------------ >> [ 0.004167] WARNING: at kernel/sched.c:4364 sub_preempt_count+0xae/0xc0() >> [ 0.004266] Hardware name: HP Compaq nx7300 (GB848ES#ACB) >> [ 0.004361] Modules linked in: >> [ 0.004497] Pid: 0, comm: swapper Not tainted 2.6.28-rc8-next-20081211 #117 >> [ 0.004595] Call Trace: >> [ 0.004689] [<c01324d6>] warn_slowpath+0x86/0xa0 >> [ 0.004789] [<c0155d00>] ? check_usage_forwards+0x10/0xb0 >> [ 0.004886] [<c015394a>] ? save_trace+0x3a/0xa0 >> [ 0.004981] [<c015742d>] ? mark_lock+0x37d/0xe00 >> [ 0.005076] [<c01580f9>] ? __lock_acquire+0x249/0x610 >> [ 0.005175] [<c04a3a02>] ? _spin_unlock_irq+0x22/0x50 >> [ 0.005272] [<c0158e50>] ? trace_hardirqs_on_caller+0x70/0x1a0 >> [ 0.005369] [<c04a3a0d>] ? _spin_unlock_irq+0x2d/0x50 >> [ 0.005465] [<c0124bfe>] sub_preempt_count+0xae/0xc0 >> [ 0.005564] [<c0137012>] _local_bh_enable+0x52/0xc0 >> [ 0.005661] [<c013725f>] __do_softirq+0x11f/0x170 >> [ 0.005756] [<c0137140>] ? __do_softirq+0x0/0x170 >> [ 0.005851] <IRQ> [<c0137729>] ? irq_exit+0x89/0xa0 >> [ 0.005993] [<c01059ed>] ? do_IRQ+0xad/0x120 >> [ 0.006088] [<c0103aac>] ? common_interrupt+0x2c/0x34 >> [ 0.006184] [<c013007b>] ? mmput+0x2b/0xc0 >> [ 0.006281] [<c06735a8>] ? check_bugs+0xb8/0xe0 >> [ 0.006379] [<c066b7ea>] ? start_kernel+0x26a/0x310 >> [ 0.006475] [<c066b270>] ? unknown_bootoption+0x0/0x210 >> [ 0.006572] [<c066b077>] ? __init_begin+0x77/0xb0 >> [ 0.006674] ---[ end trace 4eaa2a86a8e2da22 ]--- >> [ 0.016004] OK. >> [ 0.016560] ACPI: Core revision 20081031 >> [ 0.044495] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1 >> >> Config and full dmesg attached. >> > > The warning can also be reproduced in qemu, so it was easy to bisect. > > commit 7317d7b87edb41a9135e30be1ec3f7ef817c53dd > Author: Nick Piggin <nickpiggin@...oo.com.au> > Date: Tue Sep 30 20:50:27 2008 +1000 > > sched: improve preempt debugging > > This patch helped me out with a problem I recently had.... > > Basically, when the kernel lock is held, then preempt_count > underflow does not > get detected until it is released which may be a long time (and arbitrarily, > eg at different points it may be rescheduled). If the bkl is released at > schedule, the resulting output is actually fairly cryptic... > > With any other lock that elevates preempt_count, it is illegal to schedule > under it (which would get found pretty quickly). bkl allows scheduling with > preempt_count elevated, which makes underflows hard to debug. > > Signed-off-by: Ingo Molnar <mingo@...e.hu> > > I understand that not this particular commit is buggy, but at least > I've got someone to add to the CC. ;) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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