Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)
From: Eran Liberty
Date: Wed Aug 20 2008 - 09:38:49 EST
Steven Rostedt wrote:
On Wed, 20 Aug 2008, Steven Rostedt wrote:
On Wed, 20 Aug 2008, Benjamin Herrenschmidt wrote:
Found the problem (or at least -a- problem), it's a gcc bug.
Well, first I must say the code generated by -pg is just plain
horrible :-)
Appart from that, look at the exit of, for example, __d_lookup, as
generated by gcc when ftrace is enabled:
c00c0498: 38 60 00 00 li r3,0
c00c049c: 81 61 00 00 lwz r11,0(r1)
c00c04a0: 80 0b 00 04 lwz r0,4(r11)
c00c04a4: 7d 61 5b 78 mr r1,r11
c00c04a8: bb 0b ff e0 lmw r24,-32(r11)
c00c04ac: 7c 08 03 a6 mtlr r0
c00c04b0: 4e 80 00 20 blr
As you can see, it restores r1 -before- it pops r24..r31 off
the stack ! I let you imagine what happens if an interrupt happens
just in between those two instructions (mr and lmw). We don't do
redzones on our ABI, so basically, the registers end up corrupted
by the interrupt.
Ouch! You've disassembled this without -pg too, and it does not have this
bug? What version of gcc do you have?
I have:
gcc (Debian 4.3.1-2) 4.3.1
c00c64c8: 81 61 00 00 lwz r11,0(r1)
c00c64cc: 7f 83 e3 78 mr r3,r28
c00c64d0: 80 0b 00 04 lwz r0,4(r11)
c00c64d4: ba eb ff dc lmw r23,-36(r11)
c00c64d8: 7d 61 5b 78 mr r1,r11
c00c64dc: 7c 08 03 a6 mtlr r0
c00c64e0: 4e 80 00 20 blr
My version looks fine. I'm thinking that this is a separate issue than
what Eran is seeing.
Eran, can you do an "objdump -dr vmlinux" and search for __d_lookup, and
print out the end of the function dump.
Thanks,
-- Steve
powerpc-linux-gnu-objdump -dr --start-address=0xc00bb584 vmlinux | head
-n 100
vmlinux: file format elf32-powerpc
Disassembly of section .text:
c00bb584 <__d_lookup>:
c00bb584: 7c 08 02 a6 mflr r0
c00bb588: 90 01 00 04 stw r0,4(r1)
c00bb58c: 4b f5 5c 51 bl c00111dc <_mcount>
c00bb590: 94 21 ff d0 stwu r1,-48(r1)
c00bb594: 7c 08 02 a6 mflr r0
c00bb598: 3d 20 9e 37 lis r9,-25033
c00bb59c: bf 01 00 10 stmw r24,16(r1)
c00bb5a0: 61 29 00 01 ori r9,r9,1
c00bb5a4: 3d 60 c0 38 lis r11,-16328
c00bb5a8: 90 01 00 34 stw r0,52(r1)
c00bb5ac: 7c 60 4a 78 xor r0,r3,r9
c00bb5b0: 54 00 d9 7e rlwinm r0,r0,27,5,31
c00bb5b4: 83 84 00 00 lwz r28,0(r4)
c00bb5b8: 7c 3f 0b 78 mr r31,r1
c00bb5bc: 81 0b 1a 2c lwz r8,6700(r11)
c00bb5c0: 39 6b 1a 2c addi r11,r11,6700
c00bb5c4: 7c 00 e2 14 add r0,r0,r28
c00bb5c8: 81 4b 00 04 lwz r10,4(r11)
c00bb5cc: 7c 09 4a 78 xor r9,r0,r9
c00bb5d0: 83 24 00 04 lwz r25,4(r4)
c00bb5d4: 7d 29 44 30 srw r9,r9,r8
c00bb5d8: 81 0b 00 08 lwz r8,8(r11)
c00bb5dc: 7d 29 02 78 xor r9,r9,r0
c00bb5e0: 83 04 00 08 lwz r24,8(r4)
c00bb5e4: 7d 29 50 38 and r9,r9,r10
c00bb5e8: 55 29 10 3a rlwinm r9,r9,2,0,29
c00bb5ec: 7c 09 40 2e lwzx r0,r9,r8
c00bb5f0: 7c 9a 23 78 mr r26,r4
c00bb5f4: 7c 7b 1b 78 mr r27,r3
c00bb5f8: 2f 80 00 00 cmpwi cr7,r0,0
c00bb5fc: 7c 1e 03 78 mr r30,r0
c00bb600: 40 be 00 14 bne+ cr7,c00bb614 <__d_lookup+0x90>
c00bb604: 48 00 00 7c b c00bb680 <__d_lookup+0xfc>
c00bb608: 83 de 00 00 lwz r30,0(r30)
c00bb60c: 2f 9e 00 00 cmpwi cr7,r30,0
c00bb610: 41 9e 00 70 beq- cr7,c00bb680 <__d_lookup+0xfc>
c00bb614: 80 1e 00 00 lwz r0,0(r30)
c00bb618: 2f 80 00 00 cmpwi cr7,r0,0
c00bb61c: 41 9e 00 08 beq- cr7,c00bb624 <__d_lookup+0xa0>
c00bb620: 7c 00 02 2c dcbt r0,r0
c00bb624: 3b be ff f4 addi r29,r30,-12
c00bb628: 80 1d 00 18 lwz r0,24(r29)
c00bb62c: 7f 80 e0 00 cmpw cr7,r0,r28
c00bb630: 40 9e ff d8 bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb634: 80 1d 00 14 lwz r0,20(r29)
c00bb638: 7f 80 d8 00 cmpw cr7,r0,r27
c00bb63c: 40 9e ff cc bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb640: 81 3b 00 48 lwz r9,72(r27)
c00bb644: 38 9d 00 18 addi r4,r29,24
c00bb648: 2f 89 00 00 cmpwi cr7,r9,0
c00bb64c: 41 9e 00 50 beq- cr7,c00bb69c <__d_lookup+0x118>
c00bb650: 80 09 00 08 lwz r0,8(r9)
c00bb654: 2f 80 00 00 cmpwi cr7,r0,0
c00bb658: 41 9e 00 44 beq- cr7,c00bb69c <__d_lookup+0x118>
c00bb65c: 7f 63 db 78 mr r3,r27
c00bb660: 7c 09 03 a6 mtctr r0
c00bb664: 7f 45 d3 78 mr r5,r26
c00bb668: 4e 80 04 21 bctrl
c00bb66c: 2f 83 00 00 cmpwi cr7,r3,0
c00bb670: 41 9e 00 50 beq- cr7,c00bb6c0 <__d_lookup+0x13c>
c00bb674: 83 de 00 00 lwz r30,0(r30)
c00bb678: 2f 9e 00 00 cmpwi cr7,r30,0
c00bb67c: 40 9e ff 98 bne+ cr7,c00bb614 <__d_lookup+0x90>
c00bb680: 38 60 00 00 li r3,0
c00bb684: 81 61 00 00 lwz r11,0(r1)
c00bb688: 80 0b 00 04 lwz r0,4(r11)
c00bb68c: 7d 61 5b 78 mr r1,r11
c00bb690: bb 0b ff e0 lmw r24,-32(r11)
c00bb694: 7c 08 03 a6 mtlr r0
c00bb698: 4e 80 00 20 blr
c00bb69c: 80 04 00 04 lwz r0,4(r4)
c00bb6a0: 7f 80 c8 00 cmpw cr7,r0,r25
c00bb6a4: 40 9e ff 64 bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb6a8: 80 64 00 08 lwz r3,8(r4)
c00bb6ac: 7f 25 cb 78 mr r5,r25
c00bb6b0: 7f 04 c3 78 mr r4,r24
c00bb6b4: 4b f5 ab 65 bl c0016218 <memcmp>
c00bb6b8: 2f 83 00 00 cmpwi cr7,r3,0
c00bb6bc: 40 9e ff 4c bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb6c0: 80 1d 00 04 lwz r0,4(r29)
c00bb6c4: 70 09 00 10 andi. r9,r0,16
c00bb6c8: 40 a2 ff b8 bne- c00bb680 <__d_lookup+0xfc>
c00bb6cc: 7c 00 e8 28 lwarx r0,0,r29
c00bb6d0: 30 00 00 01 addic r0,r0,1
c00bb6d4: 7c 00 e9 2d stwcx. r0,0,r29
c00bb6d8: 40 a2 ff f4 bne- c00bb6cc <__d_lookup+0x148>
c00bb6dc: 7f a3 eb 78 mr r3,r29
c00bb6e0: 4b ff ff a4 b c00bb684 <__d_lookup+0x100>
c00bb6e4 <d_lookup>:
c00bb6e4: 7c 08 02 a6 mflr r0
c00bb6e8: 90 01 00 04 stw r0,4(r1)
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