Re: [Patch 0/7] Per cpu thread hotplug infrastructure - V3

From: Paul E. McKenney
Date: Fri Jul 20 2012 - 10:36:20 EST

On Fri, Jul 20, 2012 at 06:47:30PM +0530, Srivatsa S. Bhat wrote:
> On 07/19/2012 05:24 AM, Paul E. McKenney wrote:
> > On Wed, Jul 18, 2012 at 11:06:52PM +0530, Srivatsa S. Bhat wrote:
> >> On 07/16/2012 08:52 PM, Paul E. McKenney wrote:
> >>> On Mon, Jul 16, 2012 at 10:42:34AM -0000, Thomas Gleixner wrote:
> >>>> The following series implements the infrastructure for parking and
> >>>> unparking kernel threads to avoid the full teardown and fork on cpu
> >>>> hotplug operations along with management infrastructure for hotplug
> >>>> and users.
> >>>>
> >>>> Changes vs. V2:
> >>>>
> >>>> Use callbacks for all functionality. Thanks to Rusty for pointing
> >>>> that out. It makes the use sites nice and simple and keeps all the
> >>>> code which would be duplicated otherwise on the core.
> >>>
> >>> Hello, Thomas,
> >>>
> >>> What version should I apply this patchset to? I tried v3.5-rc7, but
> >>> got lots of warnings (one shown below) and the watchdog patch did not
> >>> apply.
> >>>
> >>
> >> Hi Paul,
> >>
> >> This patchset applies cleanly on Thomas' smp/hotplug branch in the -tip
> >> tree.
> >
> > Thank you, Srivatsa, works much better. Still get "scheduling while
> > atomic", looking into that.
> >
>
> Got a chance to run this patchset now.. Even I am getting "scheduling while
> atomic" messages like shown below.. Hmmm...

Here is what little I have done so far (lots of completing demands on time
this week, but I should have a goodly block of time to focus on this today):

1. The failure is from the softirq modifications. Reverting that
commit gets rid of the failures.

2. As one would expect, CONFIG_PREEMPT=n kernels do not have the
problem, which of course indicates a preempt_disable() imbalance.

3. I was unable to spot the problem by inspection, but this is not
too surprising given the high level of distraction this week.

4. Instrumentation shows that preempt_count() grows slowly with
time, but with the upper bits zero. This confirms the
preempt_disable imbalance.

5. I am currently placing WARN_ONCE() calls in the code to track
this down. When I do find it, I fully expect to feel very stupid
about my efforts on #3 above. ;-)

Thanx, Paul

> Regards,
> Srivatsa S. Bhat
>
> -----------------
>
> BUG: sleeping function called from invalid context at kernel/softirq.c:748
> in_atomic(): 1, irqs_disabled(): 0, pid: 3, name: ksoftirqd/0
> INFO: lockdep is turned off.
> Pid: 3, comm: ksoftirqd/0 Tainted: G W 3.5.0-rc1-threadhotplugv3-debug #2
> Call Trace:
> [<ffffffff8108e7ac>] __might_sleep+0x18c/0x250
> [<ffffffff8105ea4f>] run_ksoftirqd+0x4f/0x70
> [<ffffffff810c8b97>] smpboot_thread_fn+0x157/0x1f0
> [<ffffffff810c8a40>] ? smpboot_create_threads+0x80/0x80
> [<ffffffff8107e7ee>] kthread+0xee/0x100
> [<ffffffff8158eb74>] kernel_thread_helper+0x4/0x10
> [<ffffffff815844f0>] ? retint_restore_args+0x13/0x13
> [<ffffffff8107e700>] ? __init_kthread_worker+0x70/0x70
> [<ffffffff8158eb70>] ? gs_change+0x13/0x13
> BUG: scheduling while atomic: ksoftirqd/0/3/0x1000000b
> INFO: lockdep is turned off.
> Modules linked in: ext3 jbd mbcache sd_mod crc_t10dif qla2xxx scsi_transport_fc scsi_tgt mptsas mptscsih mptbase scsi_transport_sas [last unloaded: scsi_wait_scan]
> Pid: 3, comm: ksoftirqd/0 Tainted: G W 3.5.0-rc1-threadhotplugv3-debug #2
> Call Trace:
> [<ffffffff8108d1cc>] __schedule_bug+0x6c/0x90
> [<ffffffff81582818>] __schedule+0x7c8/0x880
> [<ffffffff81092cea>] __cond_resched+0x2a/0x40
> [<ffffffff81582960>] _cond_resched+0x30/0x40
> SELinux: 2048 avtab hash slots, 250818 rules.
> [<ffffffff8105ea54>] run_ksoftirqd+0x54/0x70
> [<ffffffff810c8b97>] smpboot_thread_fn+0x157/0x1f0
> [<ffffffff810c8a40>] ? smpboot_create_threads+0x80/0x80
> [<ffffffff8107e7ee>] kthread+0xee/0x100
> [<ffffffff8158eb74>] kernel_thread_helper+0x4/0x10
> [<ffffffff815844f0>] ? retint_restore_args+0x13/0x13
> [<ffffffff8107e700>] ? __init_kthread_worker+0x70/0x70
> [<ffffffff8158eb70>] ? gs_change+0x13/0x13
>
> [...]
>
> BUG: sleeping function called from invalid context at kernel/softirq.c:748
> in_atomic(): 1, irqs_disabled(): 0, pid: 37, name: ksoftirqd/8
> INFO: lockdep is turned off.
> Pid: 37, comm: ksoftirqd/8 Tainted: G W 3.5.0-rc1-threadhotplugv3-debug #2
> Call Trace:
> [<ffffffff8108e7ac>] __might_sleep+0x18c/0x250
> [<ffffffff8105ea4f>] run_ksoftirqd+0x4f/0x70
> [<ffffffff810c8b97>] smpboot_thread_fn+0x157/0x1f0
> Welcome to [<ffffffff810c8a40>] ? smpboot_create_threads+0x80/0x80
> [<ffffffff8107e7ee>] kthread+0xee/0x100
> Red Hat [<ffffffff8158eb74>] kernel_thread_helper+0x4/0x10
> [<ffffffff815844f0>] ? retint_restore_args+0x13/0x13
> [<ffffffff8107e700>] ? __init_kthread_worker+0x70/0x70
> [<ffffffff8158eb70>] ? gs_change+0x13/0x13
> BUG: scheduling while atomic: ksoftirqd/8/37/0x10000004
> INFO: lockdep is turned off.
> Modules linked in: ext3 jbd mbcache sd_mod crc_t10dif qla2xxx scsi_transport_fc scsi_tgt mptsas mptscsih mptbase scsi_transport_sas [last unloaded: scsi_wait_scan]
> Pid: 37, comm: ksoftirqd/8 Tainted: G W 3.5.0-rc1-threadhotplugv3-debug #2
> Call Trace:
> Enterprise Linu [<ffffffff8108d1cc>] __schedule_bug+0x6c/0x90
> x Server
> [<ffffffff81582818>] __schedule+0x7c8/0x880
> [<ffffffff81092cea>] __cond_resched+0x2a/0x40
> [<ffffffff81582960>] _cond_resched+0x30/0x40
> [<ffffffff8105ea54>] run_ksoftirqd+0x54/0x70
> [<ffffffff810c8b97>] smpboot_thread_fn+0x157/0x1f0
> [<ffffffff810c8a40>] ? smpboot_create_threads+0x80/0x80
> [<ffffffff8107e7ee>] kthread+0xee/0x100
> [<ffffffff8158eb74>] kernel_thread_helper+0x4/0x10
> [<ffffffff815844f0>] ? retint_restore_args+0x13/0x13
> [<ffffffff8107e700>] ? __init_kthread_worker+0x70/0x70
> [<ffffffff8158eb70>] ? gs_change+0x13/0x13
>
> [...]
>
> BUG: scheduling while atomic: watchdog/15/64/0x0000009b
> INFO: lockdep is turned off.
> Modules linked in: ebtable_nat ebtables ipt_MASQUERADE iptable_nat nf_nat xt_CHECKSUM iptable_mangle bridge stp llc autofs4 cpufreq_powersave sunrpc cpufreq_ondemand acpi_cpufreq freq_table mperf ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 iptable_filter ip_tables ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables ipv6 dm_mirror dm_region_hash dm_log dm_round_robin scsi_dh_rdac dm_multipath vhost_net macvtap macvlan tun uinput cdc_ether usbnet mii serio_raw kvm_intel kvm microcode i2c_i801 i2c_core lpc_ich mfd_core shpchp ioatdma dca i7core_edac edac_core bnx2 dm_mod sg ext3 jbd mbcache sd_mod crc_t10dif qla2xxx scsi_transport_fc scsi_tgt mptsas mptscsih mptbase scsi_transport_sas [last unloaded: scsi_wait_scan]
> Pid: 64, comm: watchdog/15 Tainted: G W 3.5.0-rc1-threadhotplugv3-debug #2
> Call Trace:
> [<ffffffff8108d1cc>] __schedule_bug+0x6c/0x90
> [<ffffffff81582818>] __schedule+0x7c8/0x880
> [<ffffffff81582bf9>] schedule+0x29/0x70
> [<ffffffff81582f77>] schedule_preempt_disabled+0x27/0x40
> [<ffffffff810c8b33>] smpboot_thread_fn+0xf3/0x1f0
> [<ffffffff810c8a40>] ? smpboot_create_threads+0x80/0x80
> [<ffffffff8107e7ee>] kthread+0xee/0x100
> [<ffffffff8158eb74>] kernel_thread_helper+0x4/0x10
> [<ffffffff815844f0>] ? retint_restore_args+0x13/0x13
> [<ffffffff8107e700>] ? __init_kthread_worker+0x70/0x70
> [<ffffffff8158eb70>] ? gs_change+0x13/0x13
>

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