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SubjectRe: oops in proc_sys_compare
On Fri, 15 Aug 2008, Al Viro wrote:
> On Thu, Aug 14, 2008 at 07:31:06PM +0100, Hugh Dickins wrote:
> > I got this oops below, after several hours of swap-heavy kernel builds
> > in tmpfs, on 2.6.27-rc1-mm1 a couple of weeks ago. Tried to reproduce
> > it without success, then got a very similar trace (not saved) from
> > 2.6.27-rc3 itself doing the same test yesterday: again oopsing in
> > proc_sys_compare on address -16, looks like it's trying for
> > PROC_I(dentry->d_inode)->sysctl but d_inode is NULL.
> >
> > I looked to see what's been going on in fs/proc recently, and your
> > [PATCH] sanitize proc_sysctl 9043476f726802f4b00c96d0c4f418dde48d1304
> > does sound like it might be implicated. I've only seen this on
> > PowerPC G5, similar tests on x86_32 and _64 haven't shown it:
> > maybe a memory barrier needed somewhere?
>
> Bloody interesting. We never create negative hashed dentries in there and
> AFAICS we should never get d_delete() called on those... Missing barrier
> would mean serious trouble in dcache.c and not just for /proc/sys...
>
> Are you sure about oops decoding? At least disassembly of proc_sys_compare()
> in the kernel image in question would be nice to see...

Here it is: I'd changed config meanwhile, so this is from a rebuild,
but symbol addresses fit exactly with the trace (and the 2.6.27-rc1-mm1
fs/proc/proc_sysctl.c is identical to that in 2.6.27-rc3 or current git).
I did try "objdump -Sd" at first, but that just looked more confusing.

c000000000121e7c <.proc_sys_compare>:
proc_sys_compare():
/home/hugh/26271E1/fs/proc/proc_sysctl.c:383
c000000000121e7c: 7c 08 02 a6 mflr r0
c000000000121e80: fb e1 ff f0 std r31,-16(r1)
c000000000121e84: 7c a9 2b 78 mr r9,r5
c000000000121e88: 7c 9f 23 78 mr r31,r4
c000000000121e8c: f8 01 00 10 std r0,16(r1)
c000000000121e90: f8 21 ff 81 stdu r1,-128(r1)
/home/hugh/26271E1/fs/proc/proc_sysctl.c:385
c000000000121e94: 60 00 00 00 nop
c000000000121e98: 80 a4 00 04 lwz r5,4(r4)
c000000000121e9c: 80 09 00 04 lwz r0,4(r9)
c000000000121ea0: 7f 80 28 00 cmpw cr7,r0,r5
c000000000121ea4: 40 9e 00 3c bne- cr7,c000000000121ee0 <.proc_sys_compare+0x64>
/home/hugh/26271E1/fs/proc/proc_sysctl.c:387
c000000000121ea8: e8 89 00 08 ld r4,8(r9)
c000000000121eac: e8 7f 00 08 ld r3,8(r31)
c000000000121eb0: 4b f0 aa 45 bl c00000000002c8f4 <.memcmp>
c000000000121eb4: 60 00 00 00 nop
c000000000121eb8: 2f a3 00 00 cmpdi cr7,r3,0
c000000000121ebc: 40 9e 00 24 bne- cr7,c000000000121ee0 <.proc_sys_compare+0x64>
PROC_I():
/home/hugh/26271E1/fs/proc/proc_sysctl.c:384
c000000000121ec0: e9 3f ff e0 ld r9,-32(r31)
c000000000121ec4: e8 69 ff f0 ld r3,-16(r9)
c000000000121ec8: 4b f2 f8 4d bl c000000000051714 <.sysctl_is_seen>
c000000000121ecc: 60 00 00 00 nop
proc_sys_compare():
/home/hugh/26271E1/fs/proc/proc_sysctl.c:389
c000000000121ed0: 7c 63 00 34 cntlzw r3,r3
c000000000121ed4: 54 63 d9 7e rlwinm r3,r3,27,5,31
c000000000121ed8: 78 63 00 20 clrldi r3,r3,32
c000000000121edc: 48 00 00 08 b c000000000121ee4 <.proc_sys_compare+0x68>
c000000000121ee0: 38 60 00 01 li r3,1
/home/hugh/26271E1/fs/proc/proc_sysctl.c:390
c000000000121ee4: 38 21 00 80 addi r1,r1,128
c000000000121ee8: e8 01 00 10 ld r0,16(r1)
c000000000121eec: eb e1 ff f0 ld r31,-16(r1)
c000000000121ef0: 7c 08 03 a6 mtlr r0
c000000000121ef4: 4e 80 00 20 blr


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