Re: v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb_clone()

I have uploaded the VM core dump [1]. And I don’t know if these logs are helpful in the case of 
failing to get the C reproducer currently.

[1] https://github.com/dotweiba/skb_clone_atomic_inc_bug/blob/master/vmcore.gz

2017/10/21 20:24:32 reproducing crash 'unable to handle kernel paging request in __skb_clone': testing program (duration=24s, {Threaded:true Collide:true Repeat:true Procs:8 Sandb
ox:setuid Fault:false FaultCall:-1 FaultNth:0 EnableTun:true UseTmpDir:true HandleSegv:true WaitRepeat:true Debug:false Repro:true}): mmap-socket$inet_tcp-bind$inet-sendto$inet-se
ndto$inet-syz_emit_ethernet
2017/10/21 20:24:49 reproducing crash 'unable to handle kernel paging request in __skb_clone': program crashed: unable to handle kernel paging request in __skb_clone
2017/10/21 20:24:49 reproducing crash 'unable to handle kernel paging request in __skb_clone': extracting C reproducer
2017/10/21 20:24:49 reproducing crash 'unable to handle kernel paging request in __skb_clone': reproducing took 1h47m5.070207729s
2017/10/21 20:24:49 reproduction failed: no target compiler

Thanks,
Wei

On 20 Oct 2017, at 11:39 AM, Willem de Bruijn [off-list ref] wrote:

On Fri, Oct 20, 2017 at 11:14 AM, Dmitry Vyukov [off-list ref] wrote:

quoted

On Fri, Oct 20, 2017 at 4:40 PM, Wei Wei [off-list ref] wrote:

quoted

Sadly, the syzkaller characterized it as a non-reproducible bug and there were empty
repro files. But if manually executing in VM like this “./syz-execprog -executor=
./syz-executor -repeat=0 -procs=16 -cover=0 crash-log”, it crashed when executing exactly
program 1056 using log0 provided.

I failed to generate the C reproducer with syz-repro as it said “no target compiler”
in the final step. I would appreciate if you could give some hints.

syzkaller tries to use aarch64-linux-gnu-gcc when cross-compiling to arm64:
https://github.com/google/syzkaller/blob/master/sys/targets/targets.go#L62
Try to install g++-aarch64-linux-gnu.
Or how should it be done on your system?

A core dump would also be helpful to root around in and inspect
what those registers point to. Thanks for posting the various reports
on github, btw.