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https://bugs.launchpad.net/bugs/1830433
Title:
32-bit x86 kernel 4.15.0-50 crash in vmalloc_sync_all
Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Bionic:
Fix Released
Bug description:
[Impact]
Commit d653420532d580156c8486686899ea6a9eeb7bf0 in bionic enabled
kernel page table isolation for x86_32, but also introduced a kernel
bug (the BUG_ON() condition in vmalloc_sync_one()) that seems to
happen when vmalloc_sync_all() is called multiple times (e.g., in a
busy loop).
The real problem seems to be a race condition with page-table entries'
initialization that can be fixed applying the upstream commit
9bc4f28af75a91aea0ae383f50b0a430c4509303 ("x86/mm: Use WRITE_ONCE()
when setting PTEs").
[Test Case]
The bug can be easily triggered by rebooting the system a couple of
times and loading this module:
https://launchpadlibrarian.net/428142172/vmalloc-stress-test.c
[Fix]
The following upstream fix seems to resolve the problem:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9bc4f28af75a91aea0ae383f50b0a430c4509303
In addition to that the following other upstream fixes are required
(all clean cherry picks) to do a cleaner backport of
9bc4f28af75a91aea0ae383f50b0a430c4509303:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=86fa949b050184ffc53688516a6a83ae5f98d08a
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=792adb90fa724ce07c0171cbc96b9215af4b1045
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5e0fb5df2ee871b841f96f9cb6a7f2784e96aa4e
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=785a19f9d1dd8a4ab2d0633be4656653bd3de1fc
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f967db0b9ed44ec3057a28f3b28efc51df51b835
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ba6f508d0ec4adb09f0a939af6d5e19cdfa8667d
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f77084d96355f5fba8e2c1fb3a51a393b1570de7
[Regression Potential]
All upstream fixes, tested on the affected platform, backport changes
are minimal.
[Original bug report]
Hi,
I'm reproducing a kernel bug in vmalloc_sync_all() with a 32-bit x86
kernel.
The problem appears in
Linux ubuntu 4.15.0-50-generic #54-Ubuntu SMP Mon May 6 18:45:45 UTC
2019 i686 i686 i686 GNU/Linux
Kernels 4.15.0-49 and prior work fine.
The kernel 4.18.0-20-generic works fine.
This problem has not been experienced with upstream Linux kernels.
It appears that invoking vmalloc_sync_all() a few times end up
triggering this issue. This can be triggered by restarting the lttng-
sessiond service with lttng-modules-dkms installed (sometimes a few
restarts are needed to trigger the bug). This ends up unloading and
reloading those modules, which issues a few vmalloc_sync_all() as
side-effect.
I'm not reporting this issue with the "ubuntu-bug linux" command
because it crashes the system on that kernel (system hangs, no console
output).
My test system runs within a kvm virtual machine on a 64-bit host.
lsb release:
Description: Ubuntu 18.04.2 LTS
Release: 18.04
Information about my kernel:
linux-image-4.15.0-50-generic:
Installed: 4.15.0-50.54
Candidate: 4.15.0-50.54
Version table:
*** 4.15.0-50.54 500
500 http://ca.archive.ubuntu.com/ubuntu bionic-updates/main i386
Packages
500 http://security.ubuntu.com/ubuntu bionic-security/main i386
Packages
100 /var/lib/dpkg/status
Information about lttng-modules-dkms:
lttng-modules-dkms:
Installed: 2.10.5-1ubuntu1.2
Candidate: 2.10.5-1ubuntu1.2
Version table:
*** 2.10.5-1ubuntu1.2 500
500 http://ca.archive.ubuntu.com/ubuntu bionic-updates/universe i386
Packages
100 /var/lib/dpkg/status
2.10.5-1ubuntu1 500
500 http://ca.archive.ubuntu.com/ubuntu bionic/universe i386 Packages
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