2.6.23-rc4: maxcpus still broken

2.6.23-rc4: maxcpus still broken

[Alexey Dobriyan]

Every time I try to boot with maxcpus=1 it dies show_stat():

        for_each_possible_cpu(i) {
                int j;

HERE ==>        user = cputime64_add(user, kstat_cpu(i).cpustat.user);


$ grep ACPI .config
$ grep APIC .config
CONFIG_X86_GOOD_APIC=y
CONFIG_X86_IO_APIC=y
CONFIG_X86_LOCAL_APIC=y


Unable to handle kernel paging request at ffffffff804ed6e0 RIP: 
 [<ffffffff802a5cd0>] show_stat+0xc8/0x3a6
PGD 203067 PUD 207063 PMD 17fc27163 PTE 4ed000
Oops: 0000 [1] SMP 
CPU 0 
Modules linked in:
Pid: 380, comm: udevd Not tainted 2.6.23-rc4-utrace #1
RIP: 0010:[<ffffffff802a5cd0>]  [<ffffffff802a5cd0>] show_stat+0xc8/0x3a6
RSP: 0018:ffff81017ed77d88  EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: ffffffff804ed6e0 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 0000000000000022 R08: 0000000000000000 R09: 0000000000000000
R10: ffff81017fd52080 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000011d R14: 0000000000000000 R15: 00007fff33944ef0
FS:  00002b32774b26d0(0000) GS:ffffffff804aa000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: ffffffff804ed6e0 CR3: 000000017f38f000 CR4: 00000000000006a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process udevd (pid: 380, threadinfo ffff81017ed76000, task ffff81017fd52080)
Stack:  ffff81017fd52080 ffffffff802418ac ffff81017fd52810 ffff81017fd52080
 0000000000000003 ffffffff80241d15 ffff81017fd52810 ffff81017f79d668
 0000000046d3d6bf ffffffff80241e73 ffff81017f79d698 ffff81017fd52080
Call Trace:
 [<ffffffff802418ac>] check_usage_backwards+0x1e/0x43
 [<ffffffff80241d15>] mark_lock+0x367/0x47c
 [<ffffffff80241e73>] mark_held_locks+0x49/0x67
 [<ffffffff803b1cf8>] __mutex_lock_slowpath+0x254/0x26a
 [<ffffffff803b1d03>] __mutex_lock_slowpath+0x25f/0x26a
 [<ffffffff8028a216>] seq_read+0x10b/0x2a1
 [<ffffffff8028a10b>] seq_read+0x0/0x2a1
 [<ffffffff802a0590>] proc_reg_read+0x80/0x9a
 [<ffffffff80272a9b>] vfs_read+0x91/0xb5
 [<ffffffff80272dd3>] sys_read+0x45/0x6e
 [<ffffffff8020b5ae>] system_call+0x7e/0x83


Code: 48 8b 0c 02 48 01 4c 24 68 48 8b 4c 02 08 48 01 4c 24 70 48 
RIP  [<ffffffff802a5cd0>] show_stat+0xc8/0x3a6
 RSP <ffff81017ed77d88>
CR2: ffffffff804ed6e0
awk used greatest stack depth: 4272 bytes left

Re: 2.6.23-rc4: maxcpus still broken

[Michal Piotrowski]

Hi Alexey,

On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> Every time I try to boot with maxcpus=1 it dies show_stat():

Is this a regression?

Hugh fixed some issues on x86-64 commit 813409771731d80e6fa94199adf99f2269a4afc0

Regards,
Michal

-- 
LOG
http://www.stardust.webpages.pl/log/

Re: 2.6.23-rc4: maxcpus still broken

[Alexey Dobriyan]

On Wed, Aug 29, 2007 at 01:35:57AM +0200, Michal Piotrowski wrote:
> On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> > Every time I try to boot with maxcpus=1 it dies show_stat():
> 
> Is this a regression?

yep

> Hugh fixed some issues on x86-64 commit 813409771731d80e6fa94199adf99f2269a4afc0

This is 2.6.23-rc4, which has this fix, yes.

And I have second box with exactly same behaviour: x86_64 E6400, it also has ACPI=n
Turning on ACPI doesn't make it any better, though.

Re: 2.6.23-rc4: maxcpus still broken

[Hugh Dickins]

On Wed, 29 Aug 2007, Alexey Dobriyan wrote:
> On Wed, Aug 29, 2007 at 01:35:57AM +0200, Michal Piotrowski wrote:
> > On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> > > Every time I try to boot with maxcpus=1 it dies show_stat():
> > 
> > Is this a regression?
> 
> yep

A regression since when, I wonder?  Please do NOT waste any time
bisecting, but I'd be interested to know which release or -rc you
previously found it worked on.

When I gave the code a quick look, it appeared to be something
which has long been wrong; but I didn't investigate whether per-cpu
allocation has changed recently.  My _suspicion_, no more than that,
is that it might be a regression to you because you're now forced
to have CONFIG_HOTPLUG_CPU=y where you didn't need it before.

Anyway, it doesn't matter too much what it's a regression since:
it's a bug that needs fixing whatever, and should be simple.
My x86_64 was running other tests yesterday which I didn't want
to interrupt, but I'll take a look later on today.

> 
> > Hugh fixed some issues on x86-64 commit 813409771731d80e6fa94199adf99f2269a4afc0
> 
> This is 2.6.23-rc4, which has this fix, yes.
> 
> And I have second box with exactly same behaviour: x86_64 E6400, it also has ACPI=n
> Turning on ACPI doesn't make it any better, though.

Hugh

Re: 2.6.23-rc4: maxcpus still broken

[Alexey Dobriyan]

On Wed, Aug 29, 2007 at 06:03:34AM +0100, Hugh Dickins wrote:
> On Wed, 29 Aug 2007, Alexey Dobriyan wrote:
> > On Wed, Aug 29, 2007 at 01:35:57AM +0200, Michal Piotrowski wrote:
> > > On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> > > > Every time I try to boot with maxcpus=1 it dies show_stat():
> > > 
> > > Is this a regression?
> > 
> > yep
> 
> A regression since when, I wonder?

Anything before "ACPI: boot correctly with "nosmp" or "maxcpus=0"" is
fine.

Re: 2.6.23-rc4: maxcpus still broken

[Len Brown]

On Wednesday 29 August 2007 01:23, Alexey Dobriyan wrote:
> On Wed, Aug 29, 2007 at 06:03:34AM +0100, Hugh Dickins wrote:
> > On Wed, 29 Aug 2007, Alexey Dobriyan wrote:
> > > On Wed, Aug 29, 2007 at 01:35:57AM +0200, Michal Piotrowski wrote:
> > > > On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> > > > > Every time I try to boot with maxcpus=1 it dies show_stat():
> > > > 
> > > > Is this a regression?
> > > 
> > > yep
> > 
> > A regression since when, I wonder?
> 
> Anything before "ACPI: boot correctly with "nosmp" or "maxcpus=0"" is
> fine.

In 2.6.23-rc4, maxcpus=1 is working for me, with and without acpi=off.
Can you post the failing .config?

thanks,
-Len

Re: 2.6.23-rc4: maxcpus still broken

[Alexey Dobriyan]

On Wed, Aug 29, 2007 at 02:41:35AM -0400, Len Brown wrote:
> On Wednesday 29 August 2007 01:23, Alexey Dobriyan wrote:
> > On Wed, Aug 29, 2007 at 06:03:34AM +0100, Hugh Dickins wrote:
> > > On Wed, 29 Aug 2007, Alexey Dobriyan wrote:
> > > > On Wed, Aug 29, 2007 at 01:35:57AM +0200, Michal Piotrowski wrote:
> > > > > On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> > > > > > Every time I try to boot with maxcpus=1 it dies show_stat():
> > > > > 
> > > > > Is this a regression?
> > > > 
> > > > yep
> > > 
> > > A regression since when, I wonder?
> > 
> > Anything before "ACPI: boot correctly with "nosmp" or "maxcpus=0"" is
> > fine.
> 
> In 2.6.23-rc4, maxcpus=1 is working for me, with and without acpi=off.
> Can you post the failing .config?

#
# Automatically generated make config: don't edit
# Linux kernel version: 2.6.23-rc4
# Wed Aug 29 11:07:23 2007
#
CONFIG_X86_64=y
CONFIG_64BIT=y
CONFIG_X86=y
CONFIG_GENERIC_TIME=y
CONFIG_GENERIC_TIME_VSYSCALL=y
CONFIG_GENERIC_CMOS_UPDATE=y
CONFIG_ZONE_DMA32=y
CONFIG_LOCKDEP_SUPPORT=y
CONFIG_STACKTRACE_SUPPORT=y
CONFIG_SEMAPHORE_SLEEPERS=y
CONFIG_MMU=y
CONFIG_ZONE_DMA=y
CONFIG_QUICKLIST=y
CONFIG_NR_QUICK=2
CONFIG_RWSEM_GENERIC_SPINLOCK=y
CONFIG_GENERIC_HWEIGHT=y
CONFIG_GENERIC_CALIBRATE_DELAY=y
CONFIG_X86_CMPXCHG=y
CONFIG_EARLY_PRINTK=y
CONFIG_GENERIC_ISA_DMA=y
CONFIG_GENERIC_IOMAP=y
CONFIG_ARCH_MAY_HAVE_PC_FDC=y
CONFIG_ARCH_POPULATES_NODE_MAP=y
CONFIG_DMI=y
CONFIG_AUDIT_ARCH=y
CONFIG_GENERIC_BUG=y
# CONFIG_ARCH_HAS_ILOG2_U32 is not set
# CONFIG_ARCH_HAS_ILOG2_U64 is not set
CONFIG_DEFCONFIG_LIST="/lib/modules/$UNAME_RELEASE/.config"

#
# General setup
#
CONFIG_EXPERIMENTAL=y
CONFIG_LOCK_KERNEL=y
CONFIG_INIT_ENV_ARG_LIMIT=32
CONFIG_LOCALVERSION=""
# CONFIG_LOCALVERSION_AUTO is not set
CONFIG_SWAP=y
CONFIG_SYSVIPC=y
CONFIG_SYSVIPC_SYSCTL=y
# CONFIG_POSIX_MQUEUE is not set
# CONFIG_BSD_PROCESS_ACCT is not set
# CONFIG_TASKSTATS is not set
# CONFIG_USER_NS is not set
# CONFIG_AUDIT is not set
CONFIG_IKCONFIG=y
CONFIG_IKCONFIG_PROC=y
CONFIG_LOG_BUF_SHIFT=15
# CONFIG_CPUSETS is not set
CONFIG_SYSFS_DEPRECATED=y
# CONFIG_RELAY is not set
# CONFIG_BLK_DEV_INITRD is not set
# CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
CONFIG_SYSCTL=y
CONFIG_EMBEDDED=y
# CONFIG_UID16 is not set
# CONFIG_SYSCTL_SYSCALL is not set
CONFIG_KALLSYMS=y
CONFIG_KALLSYMS_ALL=y
# CONFIG_KALLSYMS_EXTRA_PASS is not set
CONFIG_HOTPLUG=y
CONFIG_PRINTK=y
CONFIG_BUG=y
CONFIG_ELF_CORE=y
CONFIG_BASE_FULL=y
CONFIG_FUTEX=y
# CONFIG_EPOLL is not set
# CONFIG_SIGNALFD is not set
# CONFIG_TIMERFD is not set
# CONFIG_EVENTFD is not set
CONFIG_SHMEM=y
# CONFIG_VM_EVENT_COUNTERS is not set
CONFIG_SLAB=y
# CONFIG_SLUB is not set
# CONFIG_SLOB is not set
CONFIG_RT_MUTEXES=y
# CONFIG_TINY_SHMEM is not set
CONFIG_BASE_SMALL=0
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
# CONFIG_MODULE_FORCE_UNLOAD is not set
# CONFIG_MODVERSIONS is not set
# CONFIG_MODULE_SRCVERSION_ALL is not set
CONFIG_KMOD=y
CONFIG_STOP_MACHINE=y
CONFIG_BLOCK=y
# CONFIG_BLK_DEV_IO_TRACE is not set
# CONFIG_BLK_DEV_BSG is not set

#
# IO Schedulers
#
CONFIG_IOSCHED_NOOP=y
# CONFIG_IOSCHED_AS is not set
# CONFIG_IOSCHED_DEADLINE is not set
CONFIG_IOSCHED_CFQ=y
# CONFIG_DEFAULT_AS is not set
# CONFIG_DEFAULT_DEADLINE is not set
CONFIG_DEFAULT_CFQ=y
# CONFIG_DEFAULT_NOOP is not set
CONFIG_DEFAULT_IOSCHED="cfq"

#
# Processor type and features
#
CONFIG_X86_PC=y
# CONFIG_X86_VSMP is not set
CONFIG_MK8=y
# CONFIG_MPSC is not set
# CONFIG_MCORE2 is not set
# CONFIG_GENERIC_CPU is not set
CONFIG_X86_L1_CACHE_BYTES=64
CONFIG_X86_L1_CACHE_SHIFT=6
CONFIG_X86_INTERNODE_CACHE_BYTES=64
CONFIG_X86_TSC=y
CONFIG_X86_GOOD_APIC=y
# CONFIG_MICROCODE is not set
# CONFIG_X86_MSR is not set
# CONFIG_X86_CPUID is not set
CONFIG_X86_IO_APIC=y
CONFIG_X86_LOCAL_APIC=y
CONFIG_MTRR=y
CONFIG_SMP=y
# CONFIG_SCHED_SMT is not set
# CONFIG_SCHED_MC is not set
CONFIG_PREEMPT_NONE=y
# CONFIG_PREEMPT_VOLUNTARY is not set
# CONFIG_PREEMPT is not set
# CONFIG_PREEMPT_BKL is not set
# CONFIG_NUMA is not set
CONFIG_ARCH_SPARSEMEM_ENABLE=y
CONFIG_ARCH_FLATMEM_ENABLE=y
CONFIG_SELECT_MEMORY_MODEL=y
CONFIG_FLATMEM_MANUAL=y
# CONFIG_DISCONTIGMEM_MANUAL is not set
# CONFIG_SPARSEMEM_MANUAL is not set
CONFIG_FLATMEM=y
CONFIG_FLAT_NODE_MEM_MAP=y
# CONFIG_SPARSEMEM_STATIC is not set
CONFIG_SPLIT_PTLOCK_CPUS=4
CONFIG_RESOURCES_64BIT=y
CONFIG_ZONE_DMA_FLAG=1
CONFIG_BOUNCE=y
CONFIG_VIRT_TO_BUS=y
CONFIG_NR_CPUS=2
CONFIG_PHYSICAL_ALIGN=0x200000
# CONFIG_HOTPLUG_CPU is not set
CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG=y
CONFIG_HPET_TIMER=y
CONFIG_IOMMU=y
# CONFIG_CALGARY_IOMMU is not set
CONFIG_SWIOTLB=y
# CONFIG_X86_MCE is not set
# CONFIG_KEXEC is not set
# CONFIG_CRASH_DUMP is not set
# CONFIG_RELOCATABLE is not set
CONFIG_PHYSICAL_START=0x200000
# CONFIG_SECCOMP is not set
# CONFIG_CC_STACKPROTECTOR is not set
# CONFIG_HZ_100 is not set
# CONFIG_HZ_250 is not set
CONFIG_HZ_300=y
# CONFIG_HZ_1000 is not set
CONFIG_HZ=300
CONFIG_K8_NB=y
CONFIG_GENERIC_HARDIRQS=y
CONFIG_GENERIC_IRQ_PROBE=y
CONFIG_ISA_DMA_API=y
CONFIG_GENERIC_PENDING_IRQ=y

#
# Power management options
#
# CONFIG_PM is not set
CONFIG_SUSPEND_SMP_POSSIBLE=y

#
# CPU Frequency scaling
#
# CONFIG_CPU_FREQ is not set

#
# Bus options (PCI etc.)
#
CONFIG_PCI=y
CONFIG_PCI_DIRECT=y
# CONFIG_PCIEPORTBUS is not set
CONFIG_ARCH_SUPPORTS_MSI=y
# CONFIG_PCI_MSI is not set
# CONFIG_PCI_DEBUG is not set
# CONFIG_HT_IRQ is not set

#
# PCCARD (PCMCIA/CardBus) support
#
# CONFIG_PCCARD is not set
# CONFIG_HOTPLUG_PCI is not set

#
# Executable file formats / Emulations
#
CONFIG_BINFMT_ELF=y
# CONFIG_BINFMT_MISC is not set
CONFIG_IA32_EMULATION=y
# CONFIG_IA32_AOUT is not set
CONFIG_COMPAT=y
CONFIG_COMPAT_FOR_U64_ALIGNMENT=y
CONFIG_SYSVIPC_COMPAT=y

#
# Networking
#
CONFIG_NET=y

#
# Networking options
#
CONFIG_PACKET=y
CONFIG_PACKET_MMAP=y
CONFIG_UNIX=y
# CONFIG_NET_KEY is not set
CONFIG_INET=y
# CONFIG_IP_MULTICAST is not set
# CONFIG_IP_ADVANCED_ROUTER is not set
CONFIG_IP_FIB_HASH=y
# CONFIG_IP_PNP is not set
# CONFIG_NET_IPIP is not set
# CONFIG_NET_IPGRE is not set
# CONFIG_ARPD is not set
# CONFIG_SYN_COOKIES is not set
# CONFIG_INET_AH is not set
# CONFIG_INET_ESP is not set
# CONFIG_INET_IPCOMP is not set
# CONFIG_INET_XFRM_TUNNEL is not set
# CONFIG_INET_TUNNEL is not set
# CONFIG_INET_XFRM_MODE_TRANSPORT is not set
# CONFIG_INET_XFRM_MODE_TUNNEL is not set
# CONFIG_INET_XFRM_MODE_BEET is not set
# CONFIG_INET_DIAG is not set
# CONFIG_TCP_CONG_ADVANCED is not set
CONFIG_TCP_CONG_CUBIC=y
CONFIG_DEFAULT_TCP_CONG="cubic"
# CONFIG_TCP_MD5SIG is not set
# CONFIG_IPV6 is not set
# CONFIG_INET6_XFRM_TUNNEL is not set
# CONFIG_INET6_TUNNEL is not set
# CONFIG_NETWORK_SECMARK is not set
# CONFIG_NETFILTER is not set
# CONFIG_IP_DCCP is not set
# CONFIG_IP_SCTP is not set
# CONFIG_TIPC is not set
# CONFIG_ATM is not set
# CONFIG_BRIDGE is not set
# CONFIG_VLAN_8021Q is not set
# CONFIG_DECNET is not set
# CONFIG_LLC2 is not set
# CONFIG_IPX is not set
# CONFIG_ATALK is not set
# CONFIG_X25 is not set
# CONFIG_LAPB is not set
# CONFIG_ECONET is not set
# CONFIG_WAN_ROUTER is not set

#
# QoS and/or fair queueing
#
# CONFIG_NET_SCHED is not set

#
# Network testing
#
# CONFIG_NET_PKTGEN is not set
# CONFIG_HAMRADIO is not set
# CONFIG_IRDA is not set
# CONFIG_BT is not set
# CONFIG_AF_RXRPC is not set

#
# Wireless
#
# CONFIG_CFG80211 is not set
# CONFIG_WIRELESS_EXT is not set
# CONFIG_MAC80211 is not set
# CONFIG_IEEE80211 is not set
# CONFIG_RFKILL is not set
# CONFIG_NET_9P is not set

#
# Device Drivers
#

#
# Generic Driver Options
#
CONFIG_STANDALONE=y
CONFIG_PREVENT_FIRMWARE_BUILD=y
CONFIG_FW_LOADER=m
# CONFIG_DEBUG_DRIVER is not set
# CONFIG_DEBUG_DEVRES is not set
# CONFIG_SYS_HYPERVISOR is not set
# CONFIG_CONNECTOR is not set
# CONFIG_MTD is not set
# CONFIG_PARPORT is not set
CONFIG_BLK_DEV=y
# CONFIG_BLK_DEV_FD is not set
# CONFIG_BLK_CPQ_DA is not set
# CONFIG_BLK_CPQ_CISS_DA is not set
# CONFIG_BLK_DEV_DAC960 is not set
# CONFIG_BLK_DEV_UMEM is not set
# CONFIG_BLK_DEV_COW_COMMON is not set
CONFIG_BLK_DEV_LOOP=y
# CONFIG_BLK_DEV_CRYPTOLOOP is not set
# CONFIG_BLK_DEV_NBD is not set
# CONFIG_BLK_DEV_SX8 is not set
# CONFIG_BLK_DEV_RAM is not set
# CONFIG_CDROM_PKTCDVD is not set
# CONFIG_ATA_OVER_ETH is not set
# CONFIG_MISC_DEVICES is not set
# CONFIG_IDE is not set

#
# SCSI device support
#
# CONFIG_RAID_ATTRS is not set
CONFIG_SCSI=y
CONFIG_SCSI_DMA=y
# CONFIG_SCSI_TGT is not set
CONFIG_SCSI_NETLINK=y
# CONFIG_SCSI_PROC_FS is not set

#
# SCSI support type (disk, tape, CD-ROM)
#
CONFIG_BLK_DEV_SD=y
# CONFIG_CHR_DEV_ST is not set
# CONFIG_CHR_DEV_OSST is not set
# CONFIG_BLK_DEV_SR is not set
# CONFIG_CHR_DEV_SG is not set
# CONFIG_CHR_DEV_SCH is not set

#
# Some SCSI devices (e.g. CD jukebox) support multiple LUNs
#
# CONFIG_SCSI_MULTI_LUN is not set
# CONFIG_SCSI_CONSTANTS is not set
# CONFIG_SCSI_LOGGING is not set
# CONFIG_SCSI_SCAN_ASYNC is not set
CONFIG_SCSI_WAIT_SCAN=m

#
# SCSI Transports
#
CONFIG_SCSI_SPI_ATTRS=y
CONFIG_SCSI_FC_ATTRS=m
CONFIG_SCSI_ISCSI_ATTRS=m
CONFIG_SCSI_SAS_ATTRS=m
CONFIG_SCSI_SAS_LIBSAS=m
# CONFIG_SCSI_SAS_ATA is not set
# CONFIG_SCSI_SAS_LIBSAS_DEBUG is not set
CONFIG_SCSI_LOWLEVEL=y
# CONFIG_ISCSI_TCP is not set
# CONFIG_BLK_DEV_3W_XXXX_RAID is not set
# CONFIG_SCSI_3W_9XXX is not set
# CONFIG_SCSI_ACARD is not set
# CONFIG_SCSI_AACRAID is not set
# CONFIG_SCSI_AIC7XXX is not set
# CONFIG_SCSI_AIC7XXX_OLD is not set
CONFIG_SCSI_AIC79XX=y
CONFIG_AIC79XX_CMDS_PER_DEVICE=32
CONFIG_AIC79XX_RESET_DELAY_MS=5000
# CONFIG_AIC79XX_DEBUG_ENABLE is not set
CONFIG_AIC79XX_DEBUG_MASK=0
# CONFIG_AIC79XX_REG_PRETTY_PRINT is not set
# CONFIG_SCSI_AIC94XX is not set
# CONFIG_SCSI_ARCMSR is not set
# CONFIG_MEGARAID_NEWGEN is not set
# CONFIG_MEGARAID_LEGACY is not set
# CONFIG_MEGARAID_SAS is not set
# CONFIG_SCSI_HPTIOP is not set
# CONFIG_SCSI_BUSLOGIC is not set
# CONFIG_SCSI_DMX3191D is not set
# CONFIG_SCSI_EATA is not set
# CONFIG_SCSI_FUTURE_DOMAIN is not set
# CONFIG_SCSI_GDTH is not set
# CONFIG_SCSI_IPS is not set
# CONFIG_SCSI_INITIO is not set
# CONFIG_SCSI_INIA100 is not set
# CONFIG_SCSI_STEX is not set
# CONFIG_SCSI_SYM53C8XX_2 is not set
# CONFIG_SCSI_IPR is not set
# CONFIG_SCSI_QLOGIC_1280 is not set
# CONFIG_SCSI_QLA_FC is not set
# CONFIG_SCSI_QLA_ISCSI is not set
# CONFIG_SCSI_LPFC is not set
# CONFIG_SCSI_DC395x is not set
# CONFIG_SCSI_DC390T is not set
# CONFIG_SCSI_DEBUG is not set
# CONFIG_SCSI_SRP is not set
CONFIG_ATA=y
# CONFIG_ATA_NONSTANDARD is not set
# CONFIG_SATA_AHCI is not set
# CONFIG_SATA_SVW is not set
# CONFIG_ATA_PIIX is not set
# CONFIG_SATA_MV is not set
# CONFIG_SATA_NV is not set
# CONFIG_PDC_ADMA is not set
# CONFIG_SATA_QSTOR is not set
# CONFIG_SATA_PROMISE is not set
# CONFIG_SATA_SX4 is not set
CONFIG_SATA_SIL=y
# CONFIG_SATA_SIL24 is not set
# CONFIG_SATA_SIS is not set
# CONFIG_SATA_ULI is not set
# CONFIG_SATA_VIA is not set
# CONFIG_SATA_VITESSE is not set
# CONFIG_SATA_INIC162X is not set
# CONFIG_PATA_ALI is not set
# CONFIG_PATA_AMD is not set
# CONFIG_PATA_ARTOP is not set
# CONFIG_PATA_ATIIXP is not set
# CONFIG_PATA_CMD640_PCI is not set
# CONFIG_PATA_CMD64X is not set
# CONFIG_PATA_CS5520 is not set
# CONFIG_PATA_CS5530 is not set
# CONFIG_PATA_CYPRESS is not set
# CONFIG_PATA_EFAR is not set
# CONFIG_ATA_GENERIC is not set
# CONFIG_PATA_HPT366 is not set
# CONFIG_PATA_HPT37X is not set
# CONFIG_PATA_HPT3X2N is not set
# CONFIG_PATA_HPT3X3 is not set
# CONFIG_PATA_IT821X is not set
# CONFIG_PATA_IT8213 is not set
# CONFIG_PATA_JMICRON is not set
# CONFIG_PATA_TRIFLEX is not set
# CONFIG_PATA_MARVELL is not set
# CONFIG_PATA_MPIIX is not set
# CONFIG_PATA_OLDPIIX is not set
# CONFIG_PATA_NETCELL is not set
# CONFIG_PATA_NS87410 is not set
# CONFIG_PATA_OPTI is not set
# CONFIG_PATA_OPTIDMA is not set
# CONFIG_PATA_PDC_OLD is not set
# CONFIG_PATA_RADISYS is not set
# CONFIG_PATA_RZ1000 is not set
# CONFIG_PATA_SC1200 is not set
# CONFIG_PATA_SERVERWORKS is not set
# CONFIG_PATA_PDC2027X is not set
# CONFIG_PATA_SIL680 is not set
# CONFIG_PATA_SIS is not set
# CONFIG_PATA_VIA is not set
# CONFIG_PATA_WINBOND is not set
# CONFIG_PATA_PLATFORM is not set
# CONFIG_MD is not set

#
# Fusion MPT device support
#
# CONFIG_FUSION is not set
# CONFIG_FUSION_SPI is not set
# CONFIG_FUSION_FC is not set
# CONFIG_FUSION_SAS is not set

#
# IEEE 1394 (FireWire) support
#
# CONFIG_FIREWIRE is not set
# CONFIG_IEEE1394 is not set
# CONFIG_I2O is not set
# CONFIG_MACINTOSH_DRIVERS is not set
CONFIG_NETDEVICES=y
# CONFIG_NETDEVICES_MULTIQUEUE is not set
# CONFIG_DUMMY is not set
# CONFIG_BONDING is not set
# CONFIG_MACVLAN is not set
# CONFIG_EQUALIZER is not set
# CONFIG_TUN is not set
# CONFIG_ARCNET is not set
# CONFIG_NET_ETHERNET is not set
CONFIG_NETDEV_1000=y
# CONFIG_ACENIC is not set
# CONFIG_DL2K is not set
# CONFIG_E1000 is not set
# CONFIG_NS83820 is not set
# CONFIG_HAMACHI is not set
# CONFIG_YELLOWFIN is not set
# CONFIG_R8169 is not set
# CONFIG_SIS190 is not set
# CONFIG_SKGE is not set
# CONFIG_SKY2 is not set
# CONFIG_VIA_VELOCITY is not set
CONFIG_TIGON3=y
# CONFIG_BNX2 is not set
# CONFIG_QLA3XXX is not set
# CONFIG_ATL1 is not set
# CONFIG_NETDEV_10000 is not set
# CONFIG_TR is not set

#
# Wireless LAN
#
# CONFIG_WLAN_PRE80211 is not set
# CONFIG_WLAN_80211 is not set
# CONFIG_WAN is not set
# CONFIG_FDDI is not set
# CONFIG_HIPPI is not set
# CONFIG_PPP is not set
# CONFIG_SLIP is not set
# CONFIG_NET_FC is not set
# CONFIG_SHAPER is not set
CONFIG_NETCONSOLE=y
CONFIG_NETPOLL=y
# CONFIG_NETPOLL_TRAP is not set
CONFIG_NET_POLL_CONTROLLER=y
# CONFIG_ISDN is not set
# CONFIG_PHONE is not set

#
# Input device support
#
CONFIG_INPUT=y
# CONFIG_INPUT_FF_MEMLESS is not set
# CONFIG_INPUT_POLLDEV is not set

#
# Userland interfaces
#
# CONFIG_INPUT_MOUSEDEV is not set
# CONFIG_INPUT_JOYDEV is not set
# CONFIG_INPUT_TSDEV is not set
CONFIG_INPUT_EVDEV=y
# CONFIG_INPUT_EVBUG is not set

#
# Input Device Drivers
#
CONFIG_INPUT_KEYBOARD=y
CONFIG_KEYBOARD_ATKBD=y
# CONFIG_KEYBOARD_SUNKBD is not set
# CONFIG_KEYBOARD_LKKBD is not set
# CONFIG_KEYBOARD_XTKBD is not set
# CONFIG_KEYBOARD_NEWTON is not set
# CONFIG_KEYBOARD_STOWAWAY is not set
# CONFIG_INPUT_MOUSE is not set
# CONFIG_INPUT_JOYSTICK is not set
# CONFIG_INPUT_TABLET is not set
# CONFIG_INPUT_TOUCHSCREEN is not set
# CONFIG_INPUT_MISC is not set

#
# Hardware I/O ports
#
CONFIG_SERIO=y
CONFIG_SERIO_I8042=y
CONFIG_SERIO_SERPORT=m
# CONFIG_SERIO_CT82C710 is not set
# CONFIG_SERIO_PCIPS2 is not set
CONFIG_SERIO_LIBPS2=y
# CONFIG_SERIO_RAW is not set
# CONFIG_GAMEPORT is not set

#
# Character devices
#
CONFIG_VT=y
CONFIG_VT_CONSOLE=y
CONFIG_HW_CONSOLE=y
# CONFIG_VT_HW_CONSOLE_BINDING is not set
# CONFIG_SERIAL_NONSTANDARD is not set

#
# Serial drivers
#
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_FIX_EARLYCON_MEM=y
CONFIG_SERIAL_8250_PCI=y
CONFIG_SERIAL_8250_NR_UARTS=4
CONFIG_SERIAL_8250_RUNTIME_UARTS=4
CONFIG_SERIAL_8250_EXTENDED=y
CONFIG_SERIAL_8250_MANY_PORTS=y
CONFIG_SERIAL_8250_SHARE_IRQ=y
# CONFIG_SERIAL_8250_DETECT_IRQ is not set
CONFIG_SERIAL_8250_RSA=y

#
# Non-8250 serial port support
#
CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y
# CONFIG_SERIAL_JSM is not set
CONFIG_UNIX98_PTYS=y
# CONFIG_LEGACY_PTYS is not set
# CONFIG_IPMI_HANDLER is not set
# CONFIG_WATCHDOG is not set
# CONFIG_HW_RANDOM is not set
CONFIG_NVRAM=m
CONFIG_RTC=m
CONFIG_GEN_RTC=m
CONFIG_GEN_RTC_X=y
# CONFIG_R3964 is not set
# CONFIG_APPLICOM is not set
CONFIG_AGP=y
CONFIG_AGP_AMD64=y
# CONFIG_AGP_INTEL is not set
# CONFIG_AGP_SIS is not set
# CONFIG_AGP_VIA is not set
# CONFIG_DRM is not set
# CONFIG_MWAVE is not set
# CONFIG_PC8736x_GPIO is not set
# CONFIG_RAW_DRIVER is not set
# CONFIG_HANGCHECK_TIMER is not set
# CONFIG_TCG_TPM is not set
# CONFIG_TELCLOCK is not set
CONFIG_DEVPORT=y
# CONFIG_I2C is not set

#
# SPI support
#
# CONFIG_SPI is not set
# CONFIG_SPI_MASTER is not set
# CONFIG_W1 is not set
# CONFIG_POWER_SUPPLY is not set
# CONFIG_HWMON is not set

#
# Multifunction device drivers
#
# CONFIG_MFD_SM501 is not set

#
# Multimedia devices
#
# CONFIG_VIDEO_DEV is not set
# CONFIG_DVB_CORE is not set
# CONFIG_DAB is not set

#
# Graphics support
#
# CONFIG_BACKLIGHT_LCD_SUPPORT is not set

#
# Display device support
#
# CONFIG_DISPLAY_SUPPORT is not set
# CONFIG_VGASTATE is not set
# CONFIG_VIDEO_OUTPUT_CONTROL is not set
# CONFIG_FB is not set

#
# Console display driver support
#
CONFIG_VGA_CONSOLE=y
# CONFIG_VGACON_SOFT_SCROLLBACK is not set
# CONFIG_VIDEO_SELECT is not set
CONFIG_DUMMY_CONSOLE=y

#
# Sound
#
# CONFIG_SOUND is not set
CONFIG_HID_SUPPORT=y
# CONFIG_HID is not set
CONFIG_USB_SUPPORT=y
CONFIG_USB_ARCH_HAS_HCD=y
CONFIG_USB_ARCH_HAS_OHCI=y
CONFIG_USB_ARCH_HAS_EHCI=y
# CONFIG_USB is not set

#
# NOTE: USB_STORAGE enables SCSI, and 'SCSI disk support'
#

#
# USB Gadget Support
#
# CONFIG_USB_GADGET is not set
# CONFIG_MMC is not set
# CONFIG_NEW_LEDS is not set
# CONFIG_INFINIBAND is not set
# CONFIG_EDAC is not set
# CONFIG_RTC_CLASS is not set

#
# DMA Engine support
#
# CONFIG_DMA_ENGINE is not set

#
# DMA Clients
#

#
# DMA Devices
#
# CONFIG_VIRTUALIZATION is not set

#
# Userspace I/O
#
# CONFIG_UIO is not set

#
# Firmware Drivers
#
# CONFIG_EDD is not set
# CONFIG_DELL_RBU is not set
# CONFIG_DCDBAS is not set
# CONFIG_DMIID is not set

#
# File systems
#
CONFIG_EXT2_FS=m
# CONFIG_EXT2_FS_XATTR is not set
# CONFIG_EXT2_FS_XIP is not set
CONFIG_EXT3_FS=y
# CONFIG_EXT3_FS_XATTR is not set
# CONFIG_EXT4DEV_FS is not set
CONFIG_JBD=y
# CONFIG_JBD_DEBUG is not set
# CONFIG_REISERFS_FS is not set
# CONFIG_JFS_FS is not set
# CONFIG_FS_POSIX_ACL is not set
# CONFIG_XFS_FS is not set
# CONFIG_GFS2_FS is not set
# CONFIG_OCFS2_FS is not set
# CONFIG_MINIX_FS is not set
# CONFIG_ROMFS_FS is not set
# CONFIG_INOTIFY is not set
# CONFIG_QUOTA is not set
# CONFIG_DNOTIFY is not set
# CONFIG_AUTOFS_FS is not set
# CONFIG_AUTOFS4_FS is not set
# CONFIG_FUSE_FS is not set

#
# CD-ROM/DVD Filesystems
#
CONFIG_ISO9660_FS=m
CONFIG_JOLIET=y
CONFIG_ZISOFS=y
# CONFIG_UDF_FS is not set

#
# DOS/FAT/NT Filesystems
#
# CONFIG_MSDOS_FS is not set
# CONFIG_VFAT_FS is not set
# CONFIG_NTFS_FS is not set

#
# Pseudo filesystems
#
CONFIG_PROC_FS=y
# CONFIG_PROC_KCORE is not set
CONFIG_PROC_SYSCTL=y
CONFIG_SYSFS=y
CONFIG_TMPFS=y
# CONFIG_TMPFS_POSIX_ACL is not set
# CONFIG_HUGETLBFS is not set
# CONFIG_HUGETLB_PAGE is not set
CONFIG_RAMFS=y
# CONFIG_CONFIGFS_FS is not set

#
# Miscellaneous filesystems
#
# CONFIG_ADFS_FS is not set
# CONFIG_AFFS_FS is not set
# CONFIG_HFS_FS is not set
# CONFIG_HFSPLUS_FS is not set
# CONFIG_BEFS_FS is not set
# CONFIG_BFS_FS is not set
# CONFIG_EFS_FS is not set
# CONFIG_CRAMFS is not set
# CONFIG_VXFS_FS is not set
# CONFIG_HPFS_FS is not set
# CONFIG_QNX4FS_FS is not set
# CONFIG_SYSV_FS is not set
# CONFIG_UFS_FS is not set

#
# Network File Systems
#
# CONFIG_NFS_FS is not set
# CONFIG_NFSD is not set
# CONFIG_SMB_FS is not set
# CONFIG_CIFS is not set
# CONFIG_NCP_FS is not set
# CONFIG_CODA_FS is not set
# CONFIG_AFS_FS is not set

#
# Partition Types
#
# CONFIG_PARTITION_ADVANCED is not set
CONFIG_MSDOS_PARTITION=y

#
# Native Language Support
#
CONFIG_NLS=m
CONFIG_NLS_DEFAULT="iso8859-1"
CONFIG_NLS_CODEPAGE_437=m
# CONFIG_NLS_CODEPAGE_737 is not set
# CONFIG_NLS_CODEPAGE_775 is not set
# CONFIG_NLS_CODEPAGE_850 is not set
# CONFIG_NLS_CODEPAGE_852 is not set
# CONFIG_NLS_CODEPAGE_855 is not set
# CONFIG_NLS_CODEPAGE_857 is not set
# CONFIG_NLS_CODEPAGE_860 is not set
# CONFIG_NLS_CODEPAGE_861 is not set
# CONFIG_NLS_CODEPAGE_862 is not set
# CONFIG_NLS_CODEPAGE_863 is not set
# CONFIG_NLS_CODEPAGE_864 is not set
# CONFIG_NLS_CODEPAGE_865 is not set
# CONFIG_NLS_CODEPAGE_866 is not set
# CONFIG_NLS_CODEPAGE_869 is not set
# CONFIG_NLS_CODEPAGE_936 is not set
# CONFIG_NLS_CODEPAGE_950 is not set
# CONFIG_NLS_CODEPAGE_932 is not set
# CONFIG_NLS_CODEPAGE_949 is not set
# CONFIG_NLS_CODEPAGE_874 is not set
# CONFIG_NLS_ISO8859_8 is not set
# CONFIG_NLS_CODEPAGE_1250 is not set
# CONFIG_NLS_CODEPAGE_1251 is not set
# CONFIG_NLS_ASCII is not set
CONFIG_NLS_ISO8859_1=m
# CONFIG_NLS_ISO8859_2 is not set
# CONFIG_NLS_ISO8859_3 is not set
# CONFIG_NLS_ISO8859_4 is not set
# CONFIG_NLS_ISO8859_5 is not set
# CONFIG_NLS_ISO8859_6 is not set
# CONFIG_NLS_ISO8859_7 is not set
# CONFIG_NLS_ISO8859_9 is not set
# CONFIG_NLS_ISO8859_13 is not set
# CONFIG_NLS_ISO8859_14 is not set
# CONFIG_NLS_ISO8859_15 is not set
# CONFIG_NLS_KOI8_R is not set
# CONFIG_NLS_KOI8_U is not set
CONFIG_NLS_UTF8=m

#
# Distributed Lock Manager
#
# CONFIG_DLM is not set

#
# Instrumentation Support
#
# CONFIG_PROFILING is not set
# CONFIG_KPROBES is not set

#
# Kernel hacking
#
CONFIG_TRACE_IRQFLAGS_SUPPORT=y
# CONFIG_PRINTK_TIME is not set
# CONFIG_ENABLE_MUST_CHECK is not set
CONFIG_MAGIC_SYSRQ=y
# CONFIG_UNUSED_SYMBOLS is not set
# CONFIG_DEBUG_FS is not set
# CONFIG_HEADERS_CHECK is not set
CONFIG_DEBUG_KERNEL=y
# CONFIG_DEBUG_SHIRQ is not set
CONFIG_DETECT_SOFTLOCKUP=y
CONFIG_SCHED_DEBUG=y
CONFIG_SCHEDSTATS=y
CONFIG_TIMER_STATS=y
CONFIG_DEBUG_SLAB=y
CONFIG_DEBUG_SLAB_LEAK=y
CONFIG_DEBUG_RT_MUTEXES=y
CONFIG_DEBUG_PI_LIST=y
# CONFIG_RT_MUTEX_TESTER is not set
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
CONFIG_LOCKDEP=y
# CONFIG_LOCK_STAT is not set
# CONFIG_DEBUG_LOCKDEP is not set
CONFIG_TRACE_IRQFLAGS=y
CONFIG_DEBUG_SPINLOCK_SLEEP=y
# CONFIG_DEBUG_LOCKING_API_SELFTESTS is not set
CONFIG_STACKTRACE=y
# CONFIG_DEBUG_KOBJECT is not set
CONFIG_DEBUG_BUGVERBOSE=y
# CONFIG_DEBUG_INFO is not set
CONFIG_DEBUG_VM=y
CONFIG_DEBUG_LIST=y
# CONFIG_FRAME_POINTER is not set
# CONFIG_FORCED_INLINING is not set
# CONFIG_RCU_TORTURE_TEST is not set
# CONFIG_FAULT_INJECTION is not set
CONFIG_DEBUG_RODATA=y
# CONFIG_IOMMU_DEBUG is not set
CONFIG_DEBUG_STACKOVERFLOW=y
CONFIG_DEBUG_STACK_USAGE=y

#
# Security options
#
# CONFIG_KEYS is not set
# CONFIG_SECURITY is not set
# CONFIG_CRYPTO is not set

#
# Library routines
#
# CONFIG_CRC_CCITT is not set
# CONFIG_CRC16 is not set
# CONFIG_CRC_ITU_T is not set
# CONFIG_CRC32 is not set
# CONFIG_CRC7 is not set
# CONFIG_LIBCRC32C is not set
CONFIG_ZLIB_INFLATE=m
CONFIG_PLIST=y
CONFIG_HAS_IOMEM=y
CONFIG_HAS_IOPORT=y
CONFIG_HAS_DMA=y

[PATCH] fix maxcpus=1 oops in show_stat()

[Hugh Dickins]

Alexey Dobriyan reports that maxcpus=1 is still broken in 2.6.23-rc4:
if CONFIG_HOTPLUG_CPU is not set, x86_64 bootup oopses in show_stat() -
for_each_possible_cpu accesses a per-cpu area which was never set up.

Alexey identified commit 61ec7567db103d537329b0db9a887db570431ff4
(ACPI: boot correctly with "nosmp" or "maxcpus=0") as the origin;
but it's not really to blame, just exposes a bug in 2.6.23-rc1's commit
8b3b295502444340dd0701855ac422fbf32e161d (Especially when !CONFIG_HOTPLUG_CPU,
avoid needlessy allocating resources for CPUs that can never become available).

rc1's test for max_cpus < 2 in start_kernel() wasn't working because
max_cpus was still NR_CPUS at that point: until rc4 moved the maxcpus
parsing earlier.  Now it sets cpu_possible_map to 1 before allocating
all possible per-cpu areas; then smp_init() expands cpu_possible_map
to cpu_present_map (0xf in my case) later on.

rc1's commit has good intentions, but expects cpu_present_map to be
limited by maxcpus, which is only the case on i386.  cpus_and(possible,
possible,present) might be good, but needs an audit of cpu_present_map
uses - there may well be assumptions that any cpu present is possible.
So stay safe for now and just revert those #ifndef CONFIG_HOTPLUG_CPU
optimizations in rc1's commit.

Signed-off-by: Hugh Dickins <hugh@veritas.com>

--- 2.6.23-rc4/init/main.c	2007-08-28 04:42:58.000000000 +0100
+++ linux/init/main.c	2007-08-30 20:45:26.000000000 +0100
@@ -397,10 +397,6 @@ static void __init smp_init(void)
 {
 	unsigned int cpu;
 
-#ifndef CONFIG_HOTPLUG_CPU
-	cpu_possible_map = cpu_present_map;
-#endif
-
 	/* FIXME: This should be done in userspace --RR */
 	for_each_present_cpu(cpu) {
 		if (num_online_cpus() >= max_cpus)
@@ -545,10 +541,6 @@ asmlinkage void __init start_kernel(void
 	setup_arch(&command_line);
 	setup_command_line(command_line);
 	unwind_setup();
-#ifndef CONFIG_HOTPLUG_CPU
-	if (max_cpus < 2)
-		cpu_possible_map = cpu_online_map;
-#endif
 	setup_per_cpu_areas();
 	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
 

Re: [PATCH] fix maxcpus=1 oops in show_stat()

[Linus Torvalds]

On Fri, 31 Aug 2007, Hugh Dickins wrote:
>
> So stay safe for now and just revert those #ifndef CONFIG_HOTPLUG_CPU
> optimizations in rc1's commit.

Thanks for the debugging, applied.

		Linus

Re: [PATCH] fix maxcpus=1 oops in show_stat()

[Alexey Dobriyan]

On Fri, Aug 31, 2007 at 04:26:50AM +0100, Hugh Dickins wrote:
> --- 2.6.23-rc4/init/main.c
> +++ linux/init/main.c
> @@ -397,10 +397,6 @@ static void __init smp_init(void)
>  {
>  	unsigned int cpu;
>  
> -#ifndef CONFIG_HOTPLUG_CPU
> -	cpu_possible_map = cpu_present_map;
> -#endif
> -
>  	/* FIXME: This should be done in userspace --RR */
>  	for_each_present_cpu(cpu) {
>  		if (num_online_cpus() >= max_cpus)
> @@ -545,10 +541,6 @@ asmlinkage void __init start_kernel(void
>  	setup_arch(&command_line);
>  	setup_command_line(command_line);
>  	unwind_setup();
> -#ifndef CONFIG_HOTPLUG_CPU
> -	if (max_cpus < 2)
> -		cpu_possible_map = cpu_online_map;
> -#endif
>  	setup_per_cpu_areas();
>  	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
>  

Works here, I'll try on another box soon.

Re: 2.6.23-rc4: maxcpus still broken

[Hugh Dickins]

On Wed, 29 Aug 2007, Hugh Dickins wrote:
> On Wed, 29 Aug 2007, Alexey Dobriyan wrote:
> > On Wed, Aug 29, 2007 at 01:35:57AM +0200, Michal Piotrowski wrote:
> > > On 28/08/07, Alexey Dobriyan <adobriyan@sw.ru> wrote:
> > > > Every time I try to boot with maxcpus=1 it dies show_stat():
> > > 
> > > Is this a regression?
> > 
> > yep
> 
> A regression since when, I wonder?  Please do NOT waste any time
> bisecting, but I'd be interested to know which release or -rc you
> previously found it worked on.

And thank you, you answered:
Anything before "ACPI: boot correctly with "nosmp" or "maxcpus=0"" is
fine.

Right, though that surprised me (and had me confused for a while,
I'd forgotten that I'd backported those mods into an earlier tree).

> 
> When I gave the code a quick look, it appeared to be something
> which has long been wrong;

So I was wrong about that.

> but I didn't investigate whether per-cpu
> allocation has changed recently.  My _suspicion_, no more than that,
> is that it might be a regression to you because you're now forced
> to have CONFIG_HOTPLUG_CPU=y where you didn't need it before.

Precisely the reverse: it only happens when CONFIG_HOTPLUG_CPU is
not set.  Which accounts for why I didn't see it when testing my
maxcpus=N fix, since I had CONFIG_HOTPLUG_CPU on at that time.

> 
> Anyway, it doesn't matter too much what it's a regression since:
> it's a bug that needs fixing whatever, and should be simple.

I've underestimated it, and done little beyond confuse myself today.
It'd be easy enough to fix, but there are probably about 20 different
ways, finding the right way is not so obvious to me.  I need to get
to understand it better tomorrow (unless someone beats me to it:
I know little of the possible, the present and the online myself).

Hugh