[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

--- Comment #7 from David Smith <dsmith at redhat dot com> ---
(In reply to David Smith from comment #6)
> 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.

Sigh. Evidently I'm blind, because the 1st module in the list is
'loop2_mod_verbose'. The 'O' flag means it is an out-of-tree module, and the
'F' flag means it was force loaded (i.e. not via dependency).

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