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SubjectRe: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)
Steven Rostedt wrote:
> On Mon, 18 Aug 2008, Eran Liberty wrote:
>
>
>> Steven Rostedt wrote:
>>
>>> Eran Liberty wrote:
>>>
>>>> After compiling a kernel with ftrace I started to experience all sorts of
>>>> crashes.
>>>>
>>> Just to make sure...
>>>
>>> ftrace enables markers too, and RCU has tracing with the markers. This may
>>> not be the problem, but I just want to eliminate as many variables as
>>> possible.
>>> Could you disable ftrace, but keep the markers on too. Also, could you
>>> enable ftrace again and turn on the FTRACE_STARTUP_TEST.
>>>
>> for the fun of it I took out all my propriety modules; so now its a non
>> tainted kernel.
>>
>> Here is the matrix:
>>
>> !FTRACE x !MARKERS => stable
>> !FTRACE x MARKERS => stable
>> FTRACE x !MARKERS => n/a (FTRACE forces MARKERS)
>> FTRACE x MARKERS => unstable
>> FTRACE x FTRACE_STARTUP_TEST x MARKERS => unstable + tests passed
>>
>
> Thanks
>
>
>> Testing tracer sched_switch: PASSED
>> Testing tracer ftrace: PASSED
>> Testing dynamic ftrace: PASSED
>>
>> Oops: Exception in kernel mode, sig: 11 [#1]
>> Exsw1600
>> Modules linked in:
>> NIP: c00bbb20 LR: c00bbb20 CTR: 00000000
>>
>
> Could you load this into gdb for me and show me the output of:
>
> gdb> li *0xc00bbb20
>
> (Assuming you compiled with debuginfo on)
>
> and...
>
> gdb> disass 0xc00bbb20
>
>
>> REGS: dd5b1c50 TRAP: 0700 Not tainted (2.6.27-rc2)
>> MSR: 00029000 <EE,ME> CR: 24082282 XER: 20000000
>> TASK = ddcce060[1707] 'find' THREAD: dd5b0000
>> GPR00: 00000000 dd5b1d00 ddcce060 dd801180 dd5b1d68 dd5b1d58 dd80125b 100234ec
>> GPR08: c0800000 00019330 0000ffff dd5b1d20 24000288 100ad874 100936f8 1008a1d0
>> GPR16: 10083f80 dd5b1e2c dd5b1d68 fffffff4 c0380000 dd5b1d60 dd5b1d58 dd802084
>> GPR24: dc3d7700 dd802018 dd5b1d68 c0380000 dd801180 dd5b1d68 00000000 dd5b1d00
>> NIP [c00bbb20] d_lookup+0x40/0x90
>> LR [c00bbb20] d_lookup+0x40/0x90
>> Call Trace:
>> [dd5b1d00] [dd5b1d58] 0xdd5b1d58 (unreliable)
>> [dd5b1d20] [c00aebc4] do_lookup+0xe8/0x220
>> [dd5b1d50] [c00b0a80] __link_path_walk+0x5a4/0xd54
>> [dd5b1dc0] [c00b1288] path_walk+0x58/0xe0
>> [dd5b1df0] [c00b13f8] do_path_lookup+0x78/0x13c
>> [dd5b1e20] [c00b20f4] user_path_at+0x64/0xac
>> [dd5b1e90] [c00a9028] vfs_lstat_fd+0x34/0x74
>> [dd5b1ec0] [c00a90fc] vfs_lstat+0x30/0x48
>> [dd5b1ed0] [c00a9144] sys_lstat64+0x30/0x5c
>> [dd5b1f40] [c0010554] ret_from_syscall+0x0/0x3c
>> Instruction dump:
>> 7c0802a6 bf61000c 3f60c038 7c3f0b78 90010024 7c7c1b78 7c9d2378 83db32a0
>> 73c00001 7f83e378 7fa4eb78 4082002f <00000000> 2f830000 409e0030 801b32a0
>>
>
> Ouch! we have a 00000000 instruction. I'm almost done with the new mcount
> record for PPC (I have it done for ppc64, I'm just porting it to 32). I'm
> thinking this new code may solve your issues too. I hate the daemon.
>
> -- Steve
>
>
>

I have attached ddd. Up on crashing it points on this line

struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
{
struct dentry * dentry = NULL;
unsigned long seq;

do {
seq = read_seqbegin(&rename_lock);
dentry = __d_lookup(parent, name); <==== ddd marker
if (dentry)
break;
} while (read_seqretry(&rename_lock, seq));
return dentry;
}

(gdb) bt
#0 d_lookup (parent=0xdd801180, name=0xd99b3d68) at fs/dcache.c:1361
#1 0xc00ae7c8 in real_lookup (nd=<value optimized out>, name=<value
optimized out>, parent=0xdd801180) at fs/namei.c:507
#2 do_lookup (nd=0xd99b3e28, name=0xd99b3d68, path=0xd99b3d58) at
fs/namei.c:825
#3 0xc00b0684 in __link_path_walk (name=0xddc23009 "", nd=0xd99b3e28)
at fs/namei.c:982
#4 0xc00b0e8c in link_path_walk (nd=<value optimized out>, name=<value
optimized out>) at fs/namei.c:570
#5 path_walk (name=0xddc23000 "/proc/mtd", nd=0xd99b3e28) at
fs/namei.c:1041
#6 0xc00b0ffc in do_path_lookup (dfd=<value optimized out>,
name=0xddc23000 "/proc/mtd", flags=<value optimized out>, nd=0xd99b3e28)
at fs/namei.c:1091
#7 0xc00b1cf8 in user_path_at (dfd=-100, name=<value optimized out>,
flags=0, path=0xd99b3e98) at fs/namei.c:1334
#8 0xc00a8c98 in vfs_lstat_fd (dfd=-578809472, name=0xd99b3d68 "",
stat=0xd99b3ed8) at fs/stat.c:83
#9 0xc00a8d6c in vfs_lstat (name=0xd99b3d68 "", stat=0xd99b3d58) at
fs/stat.c:93
#10 0xc00a8db4 in sys_lstat64 (filename=0xdd801180 "",
statbuf=0xbfe285d8) at fs/stat.c:381
#11 0xc0010554 in syscall_dotrace_cont ()

both cp & lr points to 0xC00BB724
(gdb) info registers
r0 0x0 0
r1 0xd99b3d00 3650829568
r2 0xddccf2e0 3721196256
r3 0xdd801180 3716157824
r4 0xd99b3d68 3650829672
r5 0xd99b3d58 3650829656
r6 0xdd822a5b 3716295259
r7 0x100234ec 268580076
r8 0xc0800000 3229614080
r9 0x19330 103216
r10 0xffff 65535
r11 0xd99b3d20 3650829600
r12 0x24000288 603980424
r13 0x100ad874 269146228
r14 0x100936f8 269039352
r15 0x1008a1d0 269001168
r16 0x10083f80 268976000
r17 0xd99b3e2c 3650829868
r18 0xd99b3d68 3650829672
r19 0xfffffff4 4294967284
r20 0xc0380000 3224895488
r21 0xd99b3d60 3650829664
r22 0xd99b3d58 3650829656
r23 0xdd802084 3716161668
r24 0xdc3fb280 3695161984
r25 0xdd802018 3716161560
r26 0xd99b3d68 3650829672
r27 0xc0380000 3224895488
r28 0xdd801180 3716157824
r29 0xd99b3d68 3650829672
r30 0x0 0
r31 0xd99b3d00 3650829568
pc 0xc00bb724 3221993252
cr 0x24082282 604512898
lr 0xc00bb724 3221993252
ctr 0x0 0
xer 0x20000000 536870912

(gdb) li *0xC00BB724
Line 1361 of "fs/dcache.c" starts at address 0xc00bb724 <d_lookup+64>
and ends at 0xc00bb728 <d_lookup+68>.

(gdb) disassemble 0xC00BB724
Dump of assembler code for function d_lookup:
0xc00bb6e4 <d_lookup+0>: mflr r0
0xc00bb6e8 <d_lookup+4>: stw r0,4(r1)
0xc00bb6ec <d_lookup+8>: nop
0xc00bb6f0 <d_lookup+12>: stwu r1,-32(r1)
0xc00bb6f4 <d_lookup+16>: mflr r0
0xc00bb6f8 <d_lookup+20>: stmw r27,12(r1)
0xc00bb6fc <d_lookup+24>: lis r27,-16328
0xc00bb700 <d_lookup+28>: mr r31,r1
0xc00bb704 <d_lookup+32>: stw r0,36(r1)
0xc00bb708 <d_lookup+36>: mr r28,r3
0xc00bb70c <d_lookup+40>: mr r29,r4
0xc00bb710 <d_lookup+44>: lwz r30,12960(r27)
0xc00bb714 <d_lookup+48>: andi. r0,r30,1
0xc00bb718 <d_lookup+52>: mr r3,r28
0xc00bb71c <d_lookup+56>: mr r4,r29
0xc00bb720 <d_lookup+60>: bnela- 0x2c
0xc00bb724 <d_lookup+64>: .long 0x0
0xc00bb728 <d_lookup+68>: cmpwi cr7,r3,0
0xc00bb72c <d_lookup+72>: bne- cr7,0xc00bb75c <d_lookup+120>
0xc00bb730 <d_lookup+76>: lwz r0,12960(r27)
0xc00bb734 <d_lookup+80>: cmpw cr7,r0,r30
0xc00bb738 <d_lookup+84>: beq- cr7,0xc00bb75c <d_lookup+120>
0xc00bb73c <d_lookup+88>: mr r30,r0
0xc00bb740 <d_lookup+92>: andi. r0,r30,1
0xc00bb744 <d_lookup+96>: mr r3,r28
0xc00bb748 <d_lookup+100>: mr r4,r29
0xc00bb74c <d_lookup+104>: beq+ 0xc00bb724 <d_lookup+64>
0xc00bb750 <d_lookup+108>: lwz r0,12960(r27)
0xc00bb754 <d_lookup+112>: mr r30,r0
0xc00bb758 <d_lookup+116>: b 0xc00bb740 <d_lookup+92>
0xc00bb75c <d_lookup+120>: lwz r11,0(r1)
0xc00bb760 <d_lookup+124>: lwz r0,4(r11)
0xc00bb764 <d_lookup+128>: lmw r27,-20(r11)
0xc00bb768 <d_lookup+132>: mtlr r0
0xc00bb76c <d_lookup+136>: mr r1,r11
0xc00bb770 <d_lookup+140>: blr
End of assembler dump.
(gdb)

Hope this is helpfull

Liberty





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