[LU-9698] osd-ldiskfs: unknown symbol error on patched kernel

• Type: Bug
• Resolution: Won't Fix
• Priority: Minor
• Environment: Centos6 - patched kernel
• Severity: 3
• Assignee: Oleg Drokin
• Reporter: CEA

Description

Running llmount.sh from master with a patched kernel fails with:

$> llmount.sh
[...]
insmod: error inserting '/home/user/lustre-release/lustre/tests/../osd-ldiskfs/osd_ldiskfs.ko': -1 Unknown symbol in module

Output of dmesg:

$> dmesg | tail -1
osd_diskfs Unknown symbol kallsyms_lookup_name (err 0)

The problem appears after commit 0f0a43b

Issue Links

• is related to: LU-20 patchless server kernel

Comments

[Andreas Dilger]

It looks like RHEL6 has EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol) that could be used for doing the symbol lookup, like:

#ifndef HAVE_KALLSYMS_LOOKUP_NAME
int kallsyms_strcmp(void *name, const char *symbol_name, struct module *, unsigned long symbol_address)
{
        return strcmp(name, symbol_name) == 0 ? symbol_address : 0;
}

/* Note that kallsyms_strcmp() cannot return the full symbol address, only the low 32 bits.
 * We can handle this by extracting the high word from some other kernel function */
unsigned long ll_kallsyms_lookup_name(const char *name)
{
        unsigned int low_addr = kallsyms_on_each_symbol(kallsyms_strcmp, name);

        return low_addr ? kallsyms_on_each_symbol & 0xffffffff00000000ULL | low_addr : 0;
}
#else
#define ll_kallsyms_lookup_name(name) kallsyms_lookup_name(name)
#endif

[Gerrit Updater]

Oleg Drokin ([e-mail]) uploaded a new patch: https://review.whamcloud.com/27874
Subject: LU-9698 osd-ldiskfs: See if kallsyms_lookup_name is exported
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 38e08695753f0511c2cab5109a2411ef43495ad1

[Quentin Bouget (Inactive)]

> esp since on master we don't really support rhel6 anymore

I'll switch to rhel7 then =]

[Oleg Drokin]

Hm, so I just looked and it appears that kallsyms_lookup_name is just not exported on rhel6 at all.
I guess we can have a configure check to totally disable this functionality on rhel6 esp since on master we don't really support rhel6 anymore.

[Quentin Bouget (Inactive)]

$> cat /boot/config-2.6.32.573.18.1.el6_lustre | grep KALLSYM
CONFIG_KALLSYMS=y
CONFIG_KALLSYMS_ALL=y
CONFIG_KALLSYMS_EXTRA_PASS=y

It builds alright on my machine, it's just the insmod part that doesn't work. I don't know if LLNL builder tries to run llmount.sh, it if does, it is indeed strange...
For the record, I patched the kernel myself following the procedure on the wiki a while ago.

[Oleg Drokin]

That's really strange.
What's your kernel config esp. in relation to CONFIG_KALLSYMS* ?
LLNL builder built the patch that introduced this and it pass: https://review.whamcloud.com/#/c/27549/
http://build.lustre.org/builders/CentOS%206.8%20x86_64%20%28BUILD%29/builds/5549

[Peter Jones]

Oleg

Could you please advise?

Thanks

Peter