Hi, Naresh, On Sun, Apr 12, 2020 at 12:24:57PM +0530, Naresh Kamboju wrote: > On Linux mainline kernel 5.6.0 running kselftest vm compaction_test on i386 > kernel running on x86_64 devices we have noticed this Kernel BUG followed by > Kernel panic. > > BUG: kernel NULL pointer dereference, address: 00000000 > Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009 > > Steps to reproduce: > -------------------------- > # cd /opt/kselftests/default-in-kernel/vm/ > # ./compaction_test > > [ 45.955706] kauditd_printk_skb: 15 callbacks suppressed > [ 45.955707] audit: type=1334 audit(1586671685.974:25): prog-id=13 op=UNLOAD > [ 45.968082] audit: type=1334 audit(1586671685.974:26): prog-id=12 op=UNLOAD > [ 46.008163] get_swap_device: Bad swap file entry 7007504a > [ 46.013647] BUG: kernel NULL pointer dereference, address: 00000000 I suspect this is the same issue with: https://lore.kernel.org/lkml/20200410002518.GG8179@shao2-debian/ And since this one is very easy to reproduce, I finally noticed that we have wrongly enabled uffd-wp on x86_32, which is definely not going to work... Because we'll use bit 2 of swap entry assuming that's the uffd-wp bit, while that's part of swp offset on 32bit systems. Naresh, could you try whether below change fixes the issue for you? diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 8d078642b4be..7ac524d1316e 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -149,7 +149,7 @@ config X86 select HAVE_ARCH_TRACEHOOK select HAVE_ARCH_TRANSPARENT_HUGEPAGE select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 - select HAVE_ARCH_USERFAULTFD_WP if USERFAULTFD + select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD select HAVE_ARCH_VMAP_STACK if X86_64 select HAVE_ARCH_WITHIN_STACK_FRAMES select HAVE_ASM_MODVERSIONS Thanks, -- Peter Xu
