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drm: BUG: unable to handle page fault for address: 17ec6000 #1081
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Should I report this to the DRM folks, or is it a LLVM/Clang issue because it works with GCC just fine? |
It might be worth getting them involved due to the complexity of the system.
Just because it works fine with GCC doesn't mean it is an LLVM/Clang issue. See #735 for an instance of this with amdgpu. Other than that, I do not have much else to offer at the moment from staring at the code. |
Note, as of next-20200707, arm32 and arm64 boot is broken but should be fixed in next-20200708 for reasons unrelated to LLVM: https://lore.kernel.org/dmaengine/5f036d83.1c69fb81.10199.06d0@mx.google.com/ https://lore.kernel.org/dmaengine/159404871194.45151.3076873396834992441.stgit@djiang5-desk3.ch.intel.com/ No presubmit testing is done for that reason but this has been verified locally. [skip ci] Fixes: https://travis-ci.com/github/ClangBuiltLinux/continuous-integration/jobs/358277535 Link: ClangBuiltLinux/linux#1081 Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
What does that mean; they may be important to reproduce. From the trace, it looks like just the 32b registers are being printed? Is this a 32b kernel image, or a 64b kernel image? |
Sorry, the two Linux commits for the two issues below are applied.
This is a 32-bit ( |
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This is happening for me when building unpatched Linux 5.8.9 from kernel.org with clang as well on aarch64:
I suspect the issue has to do with SRCU. |
I've asked upstream about this: https://lore.kernel.org/rcu/CAKwvOdm4AQhobdkKT08bjPGb15N58QN79XWxEaQt-P5Dk4+avQ@mail.gmail.com/T/#u |
I will have to build a kernel by hand outside of the Alpine kernel packaging but will sprinkle in some printk() this weekend as requested in that thread. |
Thanks for the reports. @kaniini please attach disassembly of the bottom most stack frame when posting traces; those go hand in hand and we typically need both to understand reports. They also need to come from precisely the same kernel image; rebuilding may change the object file (I'm not sure of the kernel's status as far as fully reproducible builds is concerned). Paul had some suggestions:
Printing via printk %p with kptr restrict should help us spot if we see the same address between these two, but in the wrong order, perhaps.
You can check the dmesg closer for any reports. I noticed that some of these functions have different definitions when
So in this case, I'd add printk's in
I don't think this is the case, %fs had a value in @paulmenzel 's report, and @kaniini 's report is arm64.
I kind of get the feeling that there may be a dangling reference to a value that's been cleaned up somewhere, too. I wonder if enabling KASAN would help find use after frees here? |
arm64 does not have |
also, |
So as it turns out, I think that @nickdesaulniers 's recent SRCU patch actually fixes this issue... https://lore.kernel.org/lkml/20200929192549.501516-1-ndesaulniers@google.com/ I can reproduce these warnings on my Raspberry Pi on |
Actually, I just decided to reply on the mailing list with that information: https://lore.kernel.org/lkml/20201006065623.GA2418984@ubuntu-m3-large-x86/. Further testing would still be appreciated! |
Thank you for the update. I did a test again with
with the Using the package clang-11 and lld-11 at version 11.0.0~+rc5-1, adding non-versioned symbolic links, an image built with
works, and the bug is not visible.
But it looks like, Nick’s patch you referenced is not in the branch,
so my problem seems to have been something else, and this issue can be closed, and a new one opened for yours on the Raspberry Pi? |
Hmmm, good to know that your issue is resolved although I cannot help but feel that the issues are somehow related given the call trace is extremely similar. I do not think we should split the bugs for now. |
Applying the SRCU patch does seem to resolve it here in light testing. |
My patch hasn't landed in mainline yet. You'll need to pick it up and apply it manually. |
Paul included the (updated) patch in his <linux-rcu.git#rcu/next> Git tree. |
I think this should be resolved by https://git.kernel.org/linus/33def8498fdde180023444b08e12b72a9efed41d. Feel free to reopen if not. |
On the Asus F2A85-M PRO with
running Debian Sid/unstable with Linux v5.8-rc4-25-gbfe91da29bfad (with some patches for LLVM/Clang/LLD) built with clang-11 and lld-11 1:11~++20200701093119+ffee8040534-1~exp1 from experimental, starting a graphical session (X.Org or Wayland) fails with a page fault:
• linux-5.8-rc4+-messages.txt
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