Re: [PATCH][GIT PULL] tracing/wakeup: move access to wakeup_cpu into spinlock

Steven Rostedt
2009-03-27T13:15:44Z

On Fri, 27 Mar 2009, Maneesh Soni wrote:
> >
> > Hi Steven,
> >
> > I still the oops with the patch,
> >
> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> > IP: [<ffffffff802d2259>] probe_wakeup_sched_switch+0xd2/0x1ac
> > PGD 1d68e9067 PUD 1e6cdf067 PMD 0
> > Oops: 0000 [#1] SMP
> > last sysfs file: /sys/devices/pci0000:0c/0000:0c:00.0/irq
> > CPU 5
> > Modules linked in: autofs4 hidp rfcomm l2cap bluetooth iptable_filter ip_tables ip6t_REJECT xt_tcpudp ip6table_filter ip6_tables x_tables ipv6 dm_mirror dm_region_hash dm_log dm_multipath scsi_dh dm_mod sbs sbshc battery ac parport_pc lp parport sg sr_mod ide_cd_mod cdrom serio_raw acpi_memhotplug button tg3 libphy i2c_piix4 i2c_core pcspkr usb_storage uhci_hcd ohci_hcd ehci_hcd aacraid sd_mod scsi_mod ext3 jbd
> > Pid: 6095, comm: cat Not tainted 2.6.29-tip-test #2 eserver xSeries 366-[88632RA]-
> > RIP: 0010:[<ffffffff802d2259>] [<ffffffff802d2259>] probe_wakeup_sched_switch+0xd2/0x1ac
> > RSP: 0000:ffff8801e6d03ea0 EFLAGS: 00010046
> > RAX: 0000000000000000 RBX: ffff8800281989a0 RCX: 0000000000000046
> > RDX: ffff8800281989a0 RSI: ffffffff8020d56d RDI: ffffffff811de480
> > RBP: ffff8801e6d03ed0 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000046
> > R13: ffff88022f232820 R14: 0000000000000000 R15: 0000000000000005
> > FS: 00007f98b94cb6e0(0000) GS:ffff88002818b000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > CR2: 0000000000000008 CR3: 0000000224595000 CR4: 00000000000006e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > Process cat (pid: 6095, threadinfo ffff8801e6d02000, task ffff8801d6935040)
> > Stack:
> > ffff8801d6935040 ffff880224981230 ffff88002819dd40 0000003b4ae00aa0
> > 00007fffc14df830 ffff88002819dd40 ffff8801e6d03f70 ffffffff806f8264
> > 0000000000000002 ffff8801e6d03f48 ffff8801d6935040 ffff88022f232820
> > Call Trace:
> > [<ffffffff806f8264>] schedule+0xd99/0x10f9
> > [<ffffffff806fb61b>] ? trace_hardirqs_on_thunk+0x3a/0x3c
> > [<ffffffff8027d2cb>] ? delayed_work_timer_fn+0x0/0x38
> > [<ffffffff8020d56d>] retint_careful+0x12/0x2e
> > Code: 2d ad de f2 00 75 77 48 63 05 ac de f2 00 48 8b 4d 00 45 89 f0 48 8b 3d 8e de f2 00 48 8b 71 08 48 8b 5c c7 28 48 8b 01 4c 89 e1 <48> 8b 50 08 e8 f6 9f ff ff 48 8b 3d 6f de f2 00 48 8b 75 d0 45
> > RIP [<ffffffff802d2259>] probe_wakeup_sched_switch+0xd2/0x1ac
> > RSP <ffff8801e6d03ea0>
> > CR2: 0000000000000008
> >
>
> I could get a kdump in my next attempt. Let me know if you want me to upload the dump
> somewhere. (700 MB compressed)
>
> Some info from the dump using gdb & crash-utility.

Thanks, this is indeed helpful.

>
> (gdb) bt full
> #0 0xffffffff802d2259 in probe_wakeup_sched_switch (rq=<value optimized out>,
> prev=Cannot access memory at address 0xffff8801d05c7ea0
> ) at kernel/trace/trace_sched_wakeup.c:157
> data = (struct trace_array_cpu *) 0xffff8800281629a0
> T0 = <value optimized out>
> T1 = <value optimized out>
> delta = <value optimized out>
> flags = 70
> pc = 0
> Cannot access memory at address 0xffff8801d05c7ed8
> (gdb) print wakeup_trace
> $7 = (struct trace_array *) 0xffffffff811de480
> (gdb) print *(struct trace_array *) 0xffffffff811de480
> $8 = {buffer = 0xffff88022f090440, entries = 1441792, cpu = 0,
> time_start = 437360893965, waiter = 0x0, data = {0xffff8800281119a0,
> 0xffff88002812c9a0, 0xffff8800281479a0, 0xffff8800281629a0,
> 0xffff88002817d9a0, 0xffff8800281989a0, 0xffff8800281b39a0,
> 0xffff8800281ce9a0, 0x0 <repeats 247 times>}}
> (gdb) print tracer_enabled
> $9 = 1
> (gdb) print wakeup_cpu
> $10 = 3
> (gdb) info threads
> 8 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> 7 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> 6 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> 5 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> * 4 process 5773 0xffffffff802d2259 in probe_wakeup_sched_switch (
> rq=<value optimized out>, prev=Cannot access memory at address 0xffff8801d05c7ea0
> ) at kernel/trace/trace_sched_wakeup.c:157
> 3 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> 2 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> 1 process 0 0xffffffff80217024 in mwait_idle ()
> at /home/maneesh/linux-2.6-tip/arch/x86/include/asm/processor.h:732
> (gdb) info registers
> rax 0x0 0
> rbx 0xffff8800281629a0 -131940722792032
> rcx 0x46 70
> rdx 0xffff8800281629a0 -131940722792032
> rsi 0xffffffff8020d56d -2145331859
> rdi 0xffffffff811de480 -2128747392
> rbp 0xffff8801d05c7ed0 0xffff8801d05c7ed0
> rsp 0xffff8801d05c7ea0 0xffff8801d05c7ea0
> r8 0x0 0
> r9 0x0 0
> r10 0xffff8801d05c7eb0 -131933604643152
> r11 0x1 1
> r12 0x46 70
> r13 0xffff88022f21d820 -131932014651360
> r14 0x0 0
> r15 0x3 3
> rip 0xffffffff802d2259 0xffffffff802d2259 <probe_wakeup_sched_switch+210>
> eflags 0x10046 [ PF ZF RF ]
> cs 0x10 16
> ss 0x0 0
> ds 0x0 0
> es 0x0 0
> fs 0x0 0
> gs 0x0 0
> fctrl 0x0 0
> fstat 0x0 0
> ftag 0x0 0
> fiseg 0x0 0
> fioff 0x0 0
> foseg 0x0 0
> fooff 0x0 0
> fop 0x0 0
> mxcsr 0x0 [ ]
> (gdb)
> ...
> ...
> 0xffffffff802d2208 <probe_wakeup_sched_switch+129>: lock xadd %ax,0xf2debf(%rip) # 0xffffffff812000d0 <wakeup_lock>
> 0xffffffff802d2211 <probe_wakeup_sched_switch+138>: cmp %ah,%al
> 0xffffffff802d2213 <probe_wakeup_sched_switch+140>: je 0xffffffff802d221f <probe_wakeup_sched_switch+152>
> 0xffffffff802d2215 <probe_wakeup_sched_switch+142>: pause
> 0xffffffff802d2217 <probe_wakeup_sched_switch+144>: mov 0xf2deb3(%rip),%al # 0xffffffff812000d0 <wakeup_lock>
> 0xffffffff802d221d <probe_wakeup_sched_switch+150>: jmp 0xffffffff802d2211 <probe_wakeup_sched_switch+138>
> 0xffffffff802d221f <probe_wakeup_sched_switch+152>: cmpl $0x0,0x9fb02a(%rip) # 0xffffffff80ccd250 <tracer_enabled>
> 0xffffffff802d2226 <probe_wakeup_sched_switch+159>: je 0xffffffff802d22ac <probe_wakeup_sched_switch+293>
> 0xffffffff802d222c <probe_wakeup_sched_switch+165>: cmp 0xf2dead(%rip),%r13 # 0xffffffff812000e0 <wakeup_task>
> 0xffffffff802d2233 <probe_wakeup_sched_switch+172>: jne 0xffffffff802d22ac <probe_wakeup_sched_switch+293>
> 0xffffffff802d2235 <probe_wakeup_sched_switch+174>: movslq 0xf2deac(%rip),%rax # 0xffffffff812000e8 <wakeup_cpu>

> 0xffffffff802d223c <probe_wakeup_sched_switch+181>: mov 0x0(%rbp),%rcx

Here we load the frame pointer into %rcx.

> 0xffffffff802d2240 <probe_wakeup_sched_switch+185>: mov %r14d,%r8d
> 0xffffffff802d2243 <probe_wakeup_sched_switch+188>: mov 0xf2de8e(%rip),%rdi # 0xffffffff812000d8 <wakeup_trace>

> 0xffffffff802d224a <probe_wakeup_sched_switch+195>: mov 0x8(%rcx),%rsi

CALLER_ADDR1 gets loaded into %rsi

> 0xffffffff802d224e <probe_wakeup_sched_switch+199>: mov 0x28(%rdi,%rax,8),%rbx

> 0xffffffff802d2253 <probe_wakeup_sched_switch+204>: mov (%rcx),%rax

We move what should be the caller of the next frame into %rax but this
ends up being NULL?

> 0xffffffff802d2256 <probe_wakeup_sched_switch+207>: mov %r12,%rcx
> 0xffffffff802d2259 <probe_wakeup_sched_switch+210>: mov 0x8(%rax),%rdx <<<<<<<<<===================== Here.

Hence, we crash.

This is really strange. CALLER_ADDR* are internal gcc
__builtin_return_address(*) functions.

Do you have CONFIG_FRAME_POINTER set?

Is this running in a virtual box or bare metal? (probably should not matter)

What version of gcc do you have?

Hmm, looking back at the call stack:

> > [<ffffffff806f8264>] schedule+0xd99/0x10f9
> > [<ffffffff806fb61b>] ? trace_hardirqs_on_thunk+0x3a/0x3c
> > [<ffffffff8027d2cb>] ? delayed_work_timer_fn+0x0/0x38
> > [<ffffffff8020d56d>] retint_careful+0x12/0x2e

I wonder if we do not set up a stack frame properly. retint_careful is
called by assembly. I'll have a look at that.

Thanks,

-- Steve

> 0xffffffff802d225d <probe_wakeup_sched_switch+214>: callq 0xffffffff802cc258 <trace_function>
> 0xffffffff802d2262 <probe_wakeup_sched_switch+219>: mov 0xf2de6f(%rip),%rdi # 0xffffffff812000d8 <wakeup_trace>
> 0xffffffff802d2269 <probe_wakeup_sched_switch+226>: mov -0x30(%rbp),%rsi
> 0xffffffff802d226d <probe_wakeup_sched_switch+230>: mov %r14d,%r8d
> 0xffffffff802d2270 <probe_wakeup_sched_switch+233>: mov %r13,%rdx
> 0xffffffff802d2273 <probe_wakeup_sched_switch+236>: mov %r12,%rcx
> 0xffffffff802d2276 <probe_wakeup_sched_switch+239>: callq 0xffffffff802cd5b---Type <return> to continue, or q <return> to quit---
> 2 <tracing_sched_switch_trace>
>
>
> Some stack from rbp
>
> crash> rd 0xffff8801d05c7ed0 50
> ffff8801d05c7ed0: ffff8801d05c7f70 ffffffff806f8264 p.\.....d.o.....
> ffff8801d05c7ee0: 0000000000000002 ffff8801d05c7f48 ........H.\.....
> ffff8801d05c7ef0: ffff8801d043d040 ffff88022f21d820 @.C..... .!/....
> ffff8801d05c7f00: ffff8801d043d3e8 0000000300000000 ..C.............
> ffff8801d05c7f10: 00007fff656c34d0 0000000000000000 .4le............
> ffff8801d05c7f20: 0000000000000000 0000000000000000 ................
> ffff8801d05c7f30: ffffffff806fb61b 00000000000cf7bd ..o.............
> ffff8801d05c7f40: 0000000000000857 00000000008c3fc0 W........?......
> ffff8801d05c7f50: 0000000000000000 00007fff656c34d0 .........4le....
> ffff8801d05c7f60: 0000000000000000 0000000000000000 ................
> ffff8801d05c7f70: 0000000000000000 ffffffff8020d56d ........m. .....
> ffff8801d05c7f80: 000000000000fe2e 0000000000000202 ................
> ffff8801d05c7f90: 0000003b4b151a30 0000000000000003 0..K;...........
> ffff8801d05c7fa0: 0000000000000004 00000000008c3fc0 .........?......
> ffff8801d05c7fb0: 00000000008c30b0 0000000000000000 .0..............
> ffff8801d05c7fc0: 00007f8e5a102de8 0000000000000000 .-.Z............
> ffff8801d05c7fd0: ffffffffffffffff 00000000004533f6 .........3E.....
> ffff8801d05c7fe0: 0000000000000033 0000000000010206 3...............
> ffff8801d05c7ff0: 00007fff656c3270 000000000000002b p2le....+.......
> ffff8801d05c8000: 0000000000000000 0000000000000000 ................
>
> and some relvant text addresses
> crash> sym ffffffff806f8264
> ffffffff806f8264 (T) schedule+3481 include/trace/sched_event_types.h: 149
> crash> sym ffffffff8020d56d
> ffffffff8020d56d (t) retint_careful+18 include/linux/kdev_t.h: 52
> crash> sym ffffffff806fb61b
> ffffffff806fb61b (T) trace_hardirqs_on_thunk+58 include/linux/hrtimer.h: 199
> crash> sym ffff880028167d40
>
> It seems CALLER_ADDR is not correct?
>
> Thanks
> Maneesh
>
>
> --
> Maneesh Soni
> Linux Technology Center
> IBM India Systems and Technology Lab,
> Bangalore, India.
>