Created attachment 1470305 [details]
Portion of systemd log showing coredump
Description of problem:
System fails to boot with kernel 4.18 on i686.
Version-Release number of selected component (if applicable):
Rawhide and F28, using any of the kernel release candidates after rc0.git2.1. On F28, systemd is what is available from official repos
With small sample size, able to reproduce 66% of time. Able to reproduce in a VM.
Steps to Reproduce:
1. Install one of the kernel 4.18 release candidates after rc0.git2.1 on a 32bit Fedora 28 install
2. Reboot and select 4.18 kernel
Booting halts, dropping to dracut prompt. Log indicates coredump. Last systemd msg prior to coredump:
Jul 24 04:41:18 localhost.localdomain systemd: var-lib-nfs-rpc_pipefs.mount: Executing: /usr/bin/mount sunrpc /var/lib/nfs/rpc_pipefs -t rpc_pipefs
I've attached a portion of the log from boot. Full log available on request.
Successful boot, leaving user at graphical login
Was able to narrow down when this showed up to somewhere between kernel dist-git commits dc16ce7d36f (good, produced rc0.git2.1) and 6a5d7f80f2 (bad, produced rc0.git5.1). The following commits would not compile, probably due to soundwire issue (fix introduced in 6a5d7f80f2):
Adding it to the i686 blocker, the SIG should track this down and fix it.
(In reply to Justin M. Forbes from comment #1)
> Adding it to the i686 blocker, the SIG should track this down and fix it.
Thanks, Justin. Working on it.
Cherry-picked dist-git commit 6a5d7f80f2 into the commits above that failed to compile. Was able to get 037431cf9 and 6cf9fb960 to compile and they don't show the segfault bug. Commit 9382c1533 compiles and does show the segfault issue, so I suspect bug was introduced. I believe this dist-git commit corresponds to kernel commit 1c8c5a9d38f6...
Finally managed to track it down to commit 24dea04767e6 in Linus's tree. Interestingly, the commit message is:
> Since LD_ABS/LD_IND instructions are now removed from the core and reimplemented through a combination of inlined BPF instructions and a slow-path helper, we can get rid of the complexity from x32 JIT.
I'll try contacting upstream and keep digging...
Created attachment 1474835 [details]
Patch to fix udev segfault issue.
Found the issue. Looks like upstream reduced the size of the stack when making the above mentioned JIT improvements. It appears that the JIT is overrunning its stack, inducing random crashes.
The patch I just added fixes the issue. Next week I'll work on submitting to upstream.
That's a great find!
We apologize for the inconvenience. There is a large number of bugs to go through and several of them have gone stale. Due to this, we are doing a mass bug update across all of the Fedora 28 kernel bugs.
Fedora 28 has now been rebased to 4.18.10-300.fc28. Please test this kernel update (or newer) and let us know if you issue has been resolved or if it is still present with the newer kernel.
If you have moved on to Fedora 29, and are still experiencing this issue, please change the version to Fedora 29.
If you experience different issues, please open a new bug report for those.
I can confirm that this isn't occurring with 4.18.10-200.fc28.i686 running on Intel Atom N270.
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