[Bug runtime/16806] kernel crash during repeated module insertion

["dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16806

David Smith <dsmith at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsmith at redhat dot com

--- Comment #6 from David Smith <dsmith at redhat dot com> ---
A correction first. The test program compilation should include the rpath flag,
so that the executable can find its library.

# gcc libloop.c -g -O -shared -fPIC -o libloop.so                         
# gcc loop2.c -g -O -lpthread -lloop -Wl,-rpath,`pwd` -L. -o loop2        

Here's a portion of the kernel log of a crash that I've seen:

=====
[  813.192482] utrace_shutdown:373 entry
[  813.196964] utrace_shutdown:392 - freeing task-specific
[  813.200937] utrace_cleanup:324 - removing engine
[  813.204778] utrace_cleanup:358 exit
[  813.208640] utrace_cleanup:324 - removing engine
[  813.212415] utrace_cleanup:324 - removing engine
[  813.216090] utrace_cleanup:358 exit
[  813.471621] BUG: unable to handle kernel paging request at 00007f09303bd000
[  813.472040] IP: [<ffffffff81176072>] anon_vma_chain_link+0x12/0x40
[  813.472040] PGD 38dd3067 PUD 38e42067 PMD 5ad2067 PTE 800000006443b065
[  813.472040] Oops: 0003 [#1] SMP 
[  813.472040] Modules linked in: loop2_mod_verbose(OF) fuse btrfs zlib_deflate
raid6_pq xor vfat msdos fat ext4 mbcache jbd2 binfmt_misc nfsv3 rpcsec_gss_krb5
nfsv4 dns_resolver nfs fscache ip6t_rpfilter ip6t_REJECT ipt_REJECT
xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables
ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle
ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle
iptable_security iptable_raw iptable_filter ip_tables snd_hda_codec_generic
ppdev snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm
kvm_amd kvm snd_page_alloc snd_timer snd serio_raw pcspkr i2c_piix4
virtio_console virtio_balloon soundcore parport_pc parport mperf
[  813.472040]  nfsd auth_rpcgss nfs_acl lockd sunrpc xfs libcrc32c sr_mod
cdrom ata_generic pata_acpi virtio_blk virtio_net cirrus syscopyarea
sysfillrect sysimgblt drm_kms_helper ttm ata_piix drm virtio_pci virtio_ring
virtio i2c_core libata floppy dm_mirror dm_region_hash dm_log dm_mod
[  813.472040] CPU: 0 PID: 6159 Comm: stapio Tainted: GF         
O--------------   3.10.0-121.el7.x86_64 #1
=====

>From that output, here's what I think is happening. The stap module cleans up
and unloads (notice 'loop2_mod_verbose' isn't in the list of linked in
modules). However, something didn't get cleaned up properly and when the kernel
accesses it later, the kernel crashes.

Now I've just got to figure out what got left behind.

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