Date:	Mon, 20 Jun 2016 06:12:54 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-renesas-soc@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab:
 lockless decision to grow cache)

On Mon, Jun 20, 2016 at 03:39:43PM +0900, Joonsoo Kim wrote:
> CCing Paul to ask some question.
> 
> On Wed, Jun 15, 2016 at 10:39:47AM +0200, Geert Uytterhoeven wrote:
> > Hi Joonsoo,
> > 
> > On Wed, Jun 15, 2016 at 4:23 AM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> > > On Tue, Jun 14, 2016 at 12:45:14PM +0200, Geert Uytterhoeven wrote:
> > >> On Tue, Jun 14, 2016 at 10:11 AM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> > >> > On Tue, Jun 14, 2016 at 09:31:23AM +0200, Geert Uytterhoeven wrote:
> > >> >> On Tue, Jun 14, 2016 at 8:24 AM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> > >> >> > On Mon, Jun 13, 2016 at 09:43:13PM +0200, Geert Uytterhoeven wrote:
> > >> >> >> On Tue, Apr 12, 2016 at 6:51 AM,  <js1304@...il.com> wrote:
> > >> >> >> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> > >> >> >> > To check whther free objects exist or not precisely, we need to grab a
> > >> >> >> > lock.  But, accuracy isn't that important because race window would be
> > >> >> >> > even small and if there is too much free object, cache reaper would reap
> > >> >> >> > it.  So, this patch makes the check for free object exisistence not to
> > >> >> >> > hold a lock.  This will reduce lock contention in heavily allocation case.
> > 
> > >> >> >> I've bisected a boot failure (no output at all) in v4.7-rc2 on emev2/kzm9d
> > >> >> >> (Renesas dual Cortex A9) to this patch, which is upstream commit
> > >> >> >> 801faf0db8947e01877920e848a4d338dd7a99e7.
> > 
> > > It's curious that synchronize_sched() has some effect in this early
> > > phase. In synchronize_sched(), rcu_blocking_is_gp() is called and
> > > it checks num_online_cpus <= 1. If so, synchronize_sched() does nothing.
> > >
> > > It would be related to might_sleep() in rcu_blocking_is_gp() but I'm not sure now.
> > >
> > > First, I'd like to confirm that num_online_cpus() is correct.
> > > Could you try following patch and give me a dmesg?
> > >
> > > Thanks.
> > >
> > > ------->8----------
> > > diff --git a/mm/slab.c b/mm/slab.c
> > > index 763096a..5b7300a 100644
> > > --- a/mm/slab.c
> > > +++ b/mm/slab.c
> > > @@ -964,8 +964,10 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep,
> > >          * guaranteed to be valid until irq is re-enabled, because it will be
> > >          * freed after synchronize_sched().
> > >          */
> > > -       if (force_change)
> > > -               synchronize_sched();
> > > +       if (force_change) {
> > > +               WARN_ON_ONCE(num_online_cpus() <= 1);
> > > +               WARN_ON_ONCE(num_online_cpus() > 1);
> > > +       }
> > 
> > Full dmesg output below.
> > 
> > I also tested whether it's the call to synchronize_sched() before or after
> > secondary CPU bringup that hangs.
> > 
> >         if (force_change && num_online_cpus() <= 1)
> >                 synchronize_sched();
> > 
> > boots.
> > 
> >         if (force_change && num_online_cpus() > 1)
> >                 synchronize_sched();
> > 
> > hangs.
> 
> Hello, Paul.
> 
> I changed slab.c to use synchronize_sched() for full memory barrier. First
> call happens on kmem_cache_init_late() and it would not be a problem
> because, at this time, num_online_cpus() <= 1 and synchronize_sched()
> would return immediately. Second call site would be shmem_init()
> and it seems that system hangs on it. Since smp is already initialized
> at that time, there would be some effect of synchronize_sched() but I
> can't imagine what's wrong here. Is it invalid moment to call
> synchronize_sched()?
> 
> Note that my x86 virtual machine works fine even if
> synchronize_sched() is called in shmem_init() but Geert's some ARM
> machines (not all ARM machine) don't work well with it.

Color me confused.

Is Geert's ARM system somehow adding the second CPU before
rcu_spawn_gp_kthread() is called, that is, before or during
early_initcall() time?

RCU does assume that its kthreads are created before the second
CPU shows up.

							Thanx, Paul

> Thanks.
> 
> > 
> > Booting Linux on physical CPU 0x0
> > Linux version 4.6.0-kzm9d-05060-g801faf0db8947e01-dirty (geert@...san)
> > (gcc version 4.9.0 (GCC) ) #84 SMP Wed Jun 15 10:20:12 CEST 2016
> > CPU: ARMv7 Processor [411fc093] revision 3 (ARMv7), cr=10c5387d
> > CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
> > Machine model: EMEV2 KZM9D Board
> > debug: ignoring loglevel setting.
> > Memory policy: Data cache writealloc
> > On node 0 totalpages: 32768
> > free_area_init_node: node 0, pgdat c09286c0, node_mem_map c7efa000
> >   Normal zone: 256 pages used for memmap
> >   Normal zone: 0 pages reserved
> >   Normal zone: 32768 pages, LIFO batch:7
> > percpu: Embedded 12 pages/cpu @c7ed9000 s19264 r8192 d21696 u49152
> > pcpu-alloc: s19264 r8192 d21696 u49152 alloc=12*4096
> > pcpu-alloc: [0] 0 [0] 1
> > Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 32512
> > Kernel command line: console=ttyS1,115200n81 ignore_loglevel
> > root=/dev/nfs ip=dhcp
> > PID hash table entries: 512 (order: -1, 2048 bytes)
> > Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
> > Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
> > Memory: 121144K/131072K available (4243K kernel code, 165K rwdata,
> > 1344K rodata, 2048K init, 264K bss, 9928K reserved, 0K cma-reserved,
> > 0K highmem)
> > Virtual kernel memory layout:
> >     vector  : 0xffff0000 - 0xffff1000   (   4 kB)
> >     fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
> >     vmalloc : 0xc8800000 - 0xff800000   ( 880 MB)
> >     lowmem  : 0xc0000000 - 0xc8000000   ( 128 MB)
> >     pkmap   : 0xbfe00000 - 0xc0000000   (   2 MB)
> >     modules : 0xbf000000 - 0xbfe00000   (  14 MB)
> >       .text : 0xc0008000 - 0xc0674eb8   (6580 kB)
> >       .init : 0xc0700000 - 0xc0900000   (2048 kB)
> >       .data : 0xc0900000 - 0xc0929420   ( 166 kB)
> >        .bss : 0xc092b000 - 0xc096d1e8   ( 265 kB)
> > Hierarchical RCU implementation.
> >  Build-time adjustment of leaf fanout to 32.
> >  RCU restricting CPUs from NR_CPUS=4 to nr_cpu_ids=2.
> > RCU: Adjusting geometry for rcu_fanout_leaf=32, nr_cpu_ids=2
> > NR_IRQS:16 nr_irqs:16 16
> > clocksource_probe: no matching clocksources found
> > sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps every
> > 21474836475000000ns
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 0 at mm/slab.c:975 setup_kmem_cache_node+0x160/0x1c8
> > Modules linked in:
> > CPU: 0 PID: 0 Comm: swapper/0 Not tainted
> > 4.6.0-kzm9d-05060-g801faf0db8947e01-dirty #84
> > Hardware name: Generic Emma Mobile EV2 (Flattened Device Tree)
> > [<c010de08>] (unwind_backtrace) from [<c010a620>] (show_stack+0x10/0x14)
> > [<c010a620>] (show_stack) from [<c02b3178>] (dump_stack+0x7c/0x9c)
> > [<c02b3178>] (dump_stack) from [<c011f9fc>] (__warn+0xcc/0xfc)
> > [<c011f9fc>] (__warn) from [<c011fad0>] (warn_slowpath_null+0x1c/0x24)
> > [<c011fad0>] (warn_slowpath_null) from [<c01ced4c>]
> > (setup_kmem_cache_node+0x160/0x1c8)
> > [<c01ced4c>] (setup_kmem_cache_node) from [<c01cf02c>]
> > (__do_tune_cpucache+0xf4/0x114)
> > [<c01cf02c>] (__do_tune_cpucache) from [<c01cf0b0>] (enable_cpucache+0x64/0xb4)
> > [<c01cf0b0>] (enable_cpucache) from [<c0710324>]
> > (kmem_cache_init_late+0x40/0x84)
> > [<c0710324>] (kmem_cache_init_late) from [<c0700af8>] (start_kernel+0x238/0x36c)
> > [<c0700af8>] (start_kernel) from [<4000807c>] (0x4000807c)
> > ---[ end trace cb88537fdc8fa200 ]---
> > Console: colour dummy device 80x30
> > Calibrating delay loop (skipped) preset value.. 1066.00 BogoMIPS (lpj=5330000)
> > pid_max: default: 32768 minimum: 301
> > Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
> > Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
> > CPU: Testing write buffer coherency: ok
> > CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
> > Setting up static identity map for 0x40100000 - 0x40100058
> > CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
> > Brought up 2 CPUs
> > SMP: Total of 2 processors activated (2132.00 BogoMIPS).
> > CPU: All CPU(s) started in SVC mode.
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 1 at mm/slab.c:976 setup_kmem_cache_node+0x198/0x1c8
> > Modules linked in:
> > CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W
> > 4.6.0-kzm9d-05060-g801faf0db8947e01-dirty #84
> > Hardware name: Generic Emma Mobile EV2 (Flattened Device Tree)
> > [<c010de08>] (unwind_backtrace) from [<c010a620>] (show_stack+0x10/0x14)
> > [<c010a620>] (show_stack) from [<c02b3178>] (dump_stack+0x7c/0x9c)
> > [<c02b3178>] (dump_stack) from [<c011f9fc>] (__warn+0xcc/0xfc)
> > [<c011f9fc>] (__warn) from [<c011fad0>] (warn_slowpath_null+0x1c/0x24)
> > [<c011fad0>] (warn_slowpath_null) from [<c01ced84>]
> > (setup_kmem_cache_node+0x198/0x1c8)
> > [<c01ced84>] (setup_kmem_cache_node) from [<c01cf02c>]
> > (__do_tune_cpucache+0xf4/0x114)
> > [<c01cf02c>] (__do_tune_cpucache) from [<c01cf0b0>] (enable_cpucache+0x64/0xb4)
> > [<c01cf0b0>] (enable_cpucache) from [<c01cf4cc>]
> > (__kmem_cache_create+0x1a0/0x1c8)
> > [<c01cf4cc>] (__kmem_cache_create) from [<c01b2904>]
> > (kmem_cache_create+0xbc/0x190)
> > [<c01b2904>] (kmem_cache_create) from [<c070d724>] (shmem_init+0x34/0xb0)
> > [<c070d724>] (shmem_init) from [<c0700cc4>] (kernel_init_freeable+0x98/0x1ec)
> > [<c0700cc4>] (kernel_init_freeable) from [<c0497760>] (kernel_init+0x8/0x110)
> > [<c0497760>] (kernel_init) from [<c0106c78>] (ret_from_fork+0x14/0x3c)
> > ---[ end trace cb88537fdc8fa201 ]---
> > devtmpfs: initialized
> > VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 1
> > clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff,
> > max_idle_ns: 19112604462750000 ns
> > pinctrl core: initialized pinctrl subsystem
> > NET: Registered protocol family 16
> > DMA: preallocated 256 KiB pool for atomic coherent allocations
> > sh-pfc e0140200.pfc: emev2_pfc support registered
> > gpiochip_find_base: found new base at 992
> > gpio gpiochip0: (e0050000.gpio): created GPIO range 0->31 ==>
> > e0140200.pfc PIN 0->31
> > gpio gpiochip0: (e0050000.gpio): added GPIO chardev (254:0)
> > gpiochip_setup_dev: registered GPIOs 992 to 1023 on device: gpiochip0
> > (e0050000.gpio)
> > gpiochip_find_base: found new base at 960
> > gpio gpiochip1: (e0050080.gpio): created GPIO range 0->31 ==>
> > e0140200.pfc PIN 32->63
> > gpio gpiochip1: (e0050080.gpio): added GPIO chardev (254:1)
> > gpiochip_setup_dev: registered GPIOs 960 to 991 on device: gpiochip1
> > (e0050080.gpio)
> > gpiochip_find_base: found new base at 928
> > gpio gpiochip2: (e0050100.gpio): created GPIO range 0->31 ==>
> > e0140200.pfc PIN 64->95
> > gpio gpiochip2: (e0050100.gpio): added GPIO chardev (254:2)
> > gpiochip_setup_dev: registered GPIOs 928 to 959 on device: gpiochip2
> > (e0050100.gpio)
> > gpiochip_find_base: found new base at 896
> > gpio gpiochip3: (e0050180.gpio): created GPIO range 0->31 ==>
> > e0140200.pfc PIN 96->127
> > gpio gpiochip3: (e0050180.gpio): added GPIO chardev (254:3)
> > gpiochip_setup_dev: registered GPIOs 896 to 927 on device: gpiochip3
> > (e0050180.gpio)
> > gpiochip_find_base: found new base at 865
> > gpio gpiochip4: (e0050200.gpio): created GPIO range 0->30 ==>
> > e0140200.pfc PIN 128->158
> > gpio gpiochip4: (e0050200.gpio): added GPIO chardev (254:4)
> > gpiochip_setup_dev: registered GPIOs 865 to 895 on device: gpiochip4
> > (e0050200.gpio)
> > gio: map hw irq = 1, irq = 35
> > gio: sense irq = 1, mode = 8
> > No ATAGs?
> > hw-breakpoint: found 5 (+1 reserved) breakpoint and 1 watchpoint registers.
> > hw-breakpoint: maximum watchpoint size is 4 bytes.
> > of_get_named_gpiod_flags: can't parse 'gpio' property of node '/regulator@0[0]'
> > of_get_named_gpiod_flags: can't parse 'gpio' property of node '/regulator@1[0]'
> > SCSI subsystem initialized
> > usbcore: registered new interface driver usbfs
> > usbcore: registered new interface driver hub
> > usbcore: registered new device driver usb
> > em_sti e0180000.timer: used for clock events
> > em_sti e0180000.timer: used for oneshot clock events
> > em_sti e0180000.timer: used as clock source
> > clocksource: e0180000.timer: mask: 0xffffffffffff max_cycles:
> > 0x1ef4687b1, max_idle_ns: 3697658158765000000 ns
> > Advanced Linux Sound Architecture Driver Initialized.
> > NET: Registered protocol family 23
> > clocksource: e0180000.timer: mask: 0xffffffffffff max_cycles:
> > 0x1ef4687b1, max_idle_ns: 112843571739654 ns
> > clocksource: Switched to clocksource e0180000.timer
> > NET: Registered protocol family 2
> > TCP established hash table entries: 1024 (order: 0, 4096 bytes)
> > TCP bind hash table entries: 1024 (order: 2, 20480 bytes)
> > TCP: Hash tables configured (established 1024 bind 1024)
> > UDP hash table entries: 256 (order: 1, 12288 bytes)
> > UDP-Lite hash table entries: 256 (order: 1, 12288 bytes)
> > NET: Registered protocol family 1
> > RPC: Registered named UNIX socket transport module.
> > RPC: Registered udp transport module.
> > RPC: Registered tcp transport module.
> > RPC: Registered tcp NFSv4.1 backchannel transport module.
> > Clockevents: could not switch to one-shot mode:
> > Clockevents: could not switch to one-shot mode: dummy_timer is not functional.
> > Could not switch to high resolution mode on CPU 0
> >  dummy_timer is not functional.
> > Could not switch to high resolution mode on CPU 1
> > hw perfevents: enabled with armv7_cortex_a9 PMU driver, 7 counters available
> > futex hash table entries: 512 (order: 3, 32768 bytes)
> > workingset: timestamp_bits=28 max_order=15 bucket_order=0
> > NFS: Registering the id_resolver key type
> > Key type id_resolver registered
> > Key type id_legacy registered
> > nfs4filelayout_init: NFSv4 File Layout Driver Registering...
> > io scheduler noop registered (default)
> > Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
> > e1020000.serial: ttyS0 at MMIO 0xe1020000 (irq = 19, base_baud =
> > 796444) is a 16550A
> > e1030000.serial: ttyS1 at MMIO 0xe1030000 (irq = 20, base_baud =
> > 7168000) is a 16550A
> > console [ttyS1] enabled
> > e1040000.serial: ttyS2 at MMIO 0xe1040000 (irq = 21, base_baud =
> > 14336000) is a 16550A
> > e1050000.serial: ttyS3 at MMIO 0xe1050000 (irq = 22, base_baud =
> > 2389333) is a 16550A
> > gio: sense irq = 1, mode = 8
> > libphy: smsc911x-mdio: probed
> > Generic PHY 20000000.etherne:01: attached PHY driver [Generic PHY]
> > (mii_bus:phy_addr=20000000.etherne:01, irq=-1)
> > smsc911x 20000000.ethernet eth0: MAC Address: 00:01:9b:04:03:cf
> > usbcore: registered new interface driver usb-storage
> > i2c /dev entries driver
> > em-i2c e0070000.i2c: Added i2c controller 0, irq 33
> > em-i2c e10a0000.i2c: Added i2c controller 1, irq 34
> > cpu cpu0: failed to get clock: -2
> > cpufreq-dt: probe of cpufreq-dt failed with error -2
> > ledtrig-cpu: registered to indicate activity on CPUs
> > usbcore: registered new interface driver usbhid
> > usbhid: USB HID core driver
> > NET: Registered protocol family 17
> > Key type dns_resolver registered
> > Registering SWP/SWPB emulation handler
> > of_get_named_gpiod_flags: parsed 'gpios' property of node
> > '/gpio_keys/button@1[0]' - status (0)
> > of_get_named_gpiod_flags: parsed 'gpios' property of node
> > '/gpio_keys/button@2[0]' - status (0)
> > of_get_named_gpiod_flags: parsed 'gpios' property of node
> > '/gpio_keys/button@3[0]' - status (0)
> > of_get_named_gpiod_flags: parsed 'gpios' property of node
> > '/gpio_keys/button@4[0]' - status (0)
> > gpio-1006 (DSW2-1): gpiod_set_debounce: missing set() or
> > set_debounce() operations
> > gio: map hw irq = 14, irq = 36
> > gio: sense irq = 14, mode = 12
> > gpio-1007 (DSW2-2): gpiod_set_debounce: missing set() or
> > set_debounce() operations
> > gio: map hw irq = 15, irq = 37
> > gio: sense irq = 15, mode = 12
> > gpio-1008 (DSW2-3): gpiod_set_debounce: missing set() or
> > set_debounce() operations
> > gio: map hw irq = 16, irq = 38
> > gio: sense irq = 16, mode = 12
> > gpio-1009 (DSW2-4): gpiod_set_debounce: missing set() or
> > set_debounce() operations
> > gio: map hw irq = 17, irq = 39
> > gio: sense irq = 17, mode = 12
> > input: gpio_keys as /devices/platform/gpio_keys/input/input0
> > hctosys: unable to open rtc device (rtc0)
> > smsc911x 20000000.ethernet eth0: SMSC911x/921x identified at 0xc8880000, IRQ: 35
> > Sending DHCP requests .., OK
> > IP-Config: Got DHCP answer from 192.168.97.254, my address is 192.168.97.215
> > IP-Config: Complete:
> >      device=eth0, hwaddr=00:01:9b:04:03:cf, ipaddr=192.168.97.215,
> > mask=255.255.255.0, gw=192.168.97.254
> >      host=192.168.97.215, domain=of.borg, nis-domain=(none)
> >      bootserver=192.168.97.254, rootserver=192.168.97.254, rootpath=
> >   nameserver0=192.168.97.254
> > ALSA device list:
> >   No soundcards found.
> > Freeing unused kernel memory: 2048K (c0700000 - c0900000)
> > sysctl: error: 'kernel.hotplug' is an unknown key
> > 
> > Gr{oetje,eeting}s,
> > 
> >                         Geert
> > 
> > --
> > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> > 
> > In personal conversations with technical people, I call myself a hacker. But
> > when I'm talking to journalists I just say "programmer" or something like that.
> >                                 -- Linus Torvalds
> > 
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@...ck.org.  For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
> > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> 

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