Bcc: Ubuntu xenial kernel panic in bpf_map_update_elem using ext4slower

[stefreak]

We reported a bug to Launchpad: https://bugs.launchpad.net/ubuntu/+source/linux-meta-lts-xenial/+bug/1763352

Using the latest Xenial LTS kernel we get a kernel panic using bcc tools.

I am not sure if this is appropriate here, but maybe there are more people affected by this – then we'd be glad for people clicking on "This affects me" to bump the bug heat.

If you know a workaround or wether this bug exists in other distributions as well would also be highly appreciated.

[stefreak]

We found out that this is an Ubuntu specific issue and submitted a patch to Launchpad to fix the crash.

[stefreak]

Now marked as duplicate of https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1763454

Canonical is working on it 👍

[brent80]

"This affects me" but glad to know someone is working on it

[stefreak]

Fix is committed :) Will be in the next release. Once it landed I will close this issue.

[brent80]

I updated today to see if it was solved with this release but it didn't work for me.
4.4.0-122-generic

```
λ ~/bcc/examples/ master uname -r
4.4.0-122-generic
λ ~/bcc/examples/ master sudo ./hello_world.py
bpf: Failed to load program: Unknown error 524
0: (b7) r1 = 2593
1: (6b) *(u16 *)(r10 -4) = r1
2: (b7) r1 = 1684828783
3: (63) *(u32 *)(r10 -8) = r1
4: (18) r1 = 0x57202c6f6c6c6548
6: (7b) *(u64 *)(r10 -16) = r1
7: (b7) r1 = 0
8: (73) *(u8 *)(r10 -2) = r1
9: (bf) r1 = r10
10: (07) r1 += -16
11: (b7) r2 = 15
12: (85) call 6
13: (b7) r0 = 0
14: (95) exit

Traceback (most recent call last):
File "./hello_world.py", line 11, in
BPF(text='int kprobe__sys_clone(void *ctx) { bpf_trace_printk("Hello, World!\n"); return 0; }').trace_print()
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 308, in __init__
self._trace_autoload()
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 916, in _trace_autoload
fn = self.load_func(func_name, BPF.KPROBE)
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 348, in load_func
(func_name, errstr))
Exception: Failed to load BPF program kprobe__sys_clone: Unknown error 524```

[stefreak]

@brent80 interesting, did this work for you before 4.4.0-119? Because if yes that's now a different regression, not a kernel panic.

[stefreak]

@brent80 I can't explain your error message but AFAIK the fixed version is not released yet (will be 4.4.0-123). A colleague of mine tested a prerelease version and it fixed the issue for us apparently. You can get the prerelease version via the proposed track: https://wiki.ubuntu.com/Testing/EnableProposed

[brent80]

@stefreak Ok. Yes it worked for me in 116, but not 119 or 122, but as you said I thought it would have been released now, but I will wait until 123

[brent80]

@stefreak
So this is still an issue for me, is this a different bug? If I load kernel 116 it works just fine.

```
λ ~/ uname -r
4.4.0-124-generic
λ ~/ cd bccλ ~/bcc/ master ls
cmake CODEOWNERS COPYRIGHT.txt Dockerfile.debian docs FAQ.txt INSTALL.md LICENSE.txt man README.md snapcraft src tools
CMakeLists.txt CONTRIBUTING-SCRIPTS.md debian Dockerfile.ubuntu examples images introspection LINKS.md QUICKSTART.md scripts SPECS tests
λ ~/bcc/ master cd examples
λ ~/bcc/examples/ master ls
CMakeLists.txt cpp hello_world.py lua networking tracing usdt_sample
λ ~/bcc/examples/ master sudo ./hello_world.py
bpf: Failed to load program: Unknown error 524
0: (b7) r1 = 2593
1: (6b) *(u16 *)(r10 -4) = r1
2: (b7) r1 = 1684828783
3: (63) *(u32 *)(r10 -8) = r1
4: (18) r1 = 0x57202c6f6c6c6548
6: (7b) *(u64 *)(r10 -16) = r1
7: (b7) r1 = 0
8: (73) *(u8 *)(r10 -2) = r1
9: (bf) r1 = r10
10: (07) r1 += -16
11: (b7) r2 = 15
12: (85) call 6
13: (b7) r0 = 0
14: (95) exit

Traceback (most recent call last):
File "./hello_world.py", line 12, in
BPF(text='int kprobe__sys_clone(void *ctx) { bpf_trace_printk("Hello, World!\n"); return 0; }').trace_print()
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 308, in __init__
self._trace_autoload()
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 916, in _trace_autoload
fn = self.load_func(func_name, BPF.KPROBE)
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 348, in load_func
(func_name, errstr))
Exception: Failed to load BPF program kprobe__sys_clone: Unknown error 524```

[damienrg]

@brent80 I had the same problem and it is fixed in 4.4.0.125-generic available in proposed.

[stefreak]

Launchpad says it is fixed now in 4.4.0-127.153 – did anyone have a chance already to test that version?

[damienrg]

Yes, it is fixed for me with 4.4.0-127.153.

[stefreak]

Cool then i'll close this issue