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    SubjectRe: linux-next: Tree for December 11

    * 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,
    > >>
    > >> Changes since 20081210:
    > >>
    > >> New tree:
    > >> nommu
    > >>
    > >> Undropped tree:
    > >> sound
    > >>
    > >> Dropped trees (temporarily):
    > >> v4l-dvb (build problem)
    > >> mtd (difficult conflicts)
    > >> drm (build problem)
    > >> semaphore-removal (due to unfixed conflicts against Linus' tree)
    > >> cpu_alloc (build problem)
    > >> perfmon3 (concerns from the x86 team)
    > >> audit (difficult conflicts)
    > >> nommu (build problem)
    > >> staging (build failure)
    > >>
    > >> The driver-core tree gained a build failure that needed a commit reverted.
    > >>
    > >> The ftrace tree gained a conflict against Linus' tree.
    > >>
    > >> The pci tree gained a conflict against the driver-core tree.
    > >>
    > >> The mtd tree gained 3 conflicts against the arm tree which I could not
    > >> easily resolve, so it was dropped.
    > >>
    > >> The ttydev tree gained a conflict against the async_tx tree requiring a
    > >> commit from the async_tx tree to be reverted.
    > >>
    > >> The nommu tree gained conflicts against the slab and kmemcheck trees and
    > >> also a build failure so it was dropped.
    > >>
    > >> ----------------------------------------------------------------------------
    > >
    > > Hi.
    > >
    > > 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. ;)
    >
    > Also the author's e-mail looks suspicious.

    Suspicious in what way?

    Ingo


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