Messages in this thread | | | Date | Thu, 19 Jul 2007 19:41:17 +0530 | From | "Satyam Sharma" <> | Subject | Re: BUG: unable to handle kernel NULL pointer dereference - nfs v3 |
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Hi Neil,
[ okay, just searching through my lkml folder looking for "unable to handle" :-) ]
On 7/17/07, Neil Brown <neilb@suse.de> wrote: > On Monday July 16, david.ml@euro-web.fr wrote: > > > > ************ > > BUG: unable to handle kernel NULL pointer dereference at virtual address > > 00000004
> > EIP is at encode_fsid+0x67/0x89 > > This is presumably where the illegal access happened. > > > eax: e5bde8c0 ebx: f7593404 ecx: 00000000 edx: 00000006 > > esi: dc569048 edi: f75934ec ebp: f7593404 esp: f75f1f18
Yup, ecx is to blame here ...
> > Code: e2 08 09 d1 09 c1 eb 10 8b 83 88 00 00 00 8b 40 30 89 c3 89 c1 c1 fb 1f > > 89 d8 0f c8 89 06 89 c8 eb 1e > > Unfortunately "ksymoops" does seem to decode this into something quite > useful enough. Normally one of the numbers has <> around it. Are you > should you copied the number across exactly?
Yes, I think David missed posting the full "Code:" here. Unfortunate.
> In any case, there is no place in encode_fsid where an offset of 4 > from any register is indexed, nor an offset of -2.
But I went ahead and disassembled encode_fsid() anyway. I did stumble across a "mov 0x4(%ecx), %edx" -- which turns out to be:
static __be32 *encode_fsid(__be32 *p, struct svc_fh *fhp) { u64 f; switch(fsid_source(fhp)) { default: case FSIDSOURCE_DEV: p = xdr_encode_hyper(p, (u64)huge_encode_dev (fhp->fh_dentry->d_inode->i_sb->s_dev)); break; case FSIDSOURCE_FSID: p = xdr_encode_hyper(p, (u64) fhp->fh_export->ex_fsid); break; case FSIDSOURCE_UUID: f = ((u64*)fhp->fh_export->ex_uuid)[0]; f ^= ((u64*)fhp->fh_export->ex_uuid)[1]; /* ***** HERE ***** */ p = xdr_encode_hyper(p, f); break; } return p; }
Note that fhp->fh_export->ex_uuid is an unsigned char *, which is 4 bytes on an i386 (which is what David's system is). For some reason fhp->fh_export->ex_uuid (%ecx) is NULL here, which leads to the oops. I have _zero_ other knowledge of knfsd code, and not really be of any other use, sorry.
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