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    SubjectRe: linux-next: Tree for December 11
    On Sun, Dec 14, 2008 at 17:34, Alexey Zaytsev <alexey.zaytsev@gmail.com> wrote:
    > On Thu, Dec 11, 2008 at 15:40, Alexey Zaytsev <alexey.zaytsev@gmail.com> wrote:
    >> On Thu, Dec 11, 2008 at 12:04, Stephen Rothwell <sfr@canb.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@yahoo.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@elte.hu>
    >
    > I understand that not this particular commit is buggy, but at least
    > I've got someone to add to the CC. ;)


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