Re: Does LOCKDEP work on ARM64?

[Will Deacon]

On Sat, Oct 24, 2020 at 11:51:49AM +0200, Dmitry Vyukov wrote:
> Hello ARM64/LOCKDEP maintainers,
> 
> I've started experimenting with running syzkaller on ARM64 using
> QEMU/TCG. Total execution speed is very low and it ran just a handful
> of tests, but I am seeing massive amounts of locking bugs. Most of
> these were not observed on x86_64, while x86_64 ran gazillions of
> tests by now and most of these are trivial to trigger (depend only on
> call stack) and they do not look ARM64-specific. So I wonder:
> 1. Are there any known issues with LOCKDEP on ARM64?
> 2. Or are all these real and it's x86_64 LOCKDEP that's misbehaving?
> 3. Or are both x86_64 and ARM64 fine and these are just somehow ARM64-specific?
> 
> Here are details. Kernel is on
> f9893351acaecf0a414baf9942b48d5bb5c688c6 (recent upstream HEAD).
> Kernel config:
> https://gist.githubusercontent.com/dvyukov/c92a1e08f3f7e22b1f0387096d98b18b/raw/9f79f83c3b018ac27a040649f7d0fef36b63b960/gistfile1.txt
> 
> Here is one "Invalid wait context". It looks like just a put_user
> inside of syscall function:
> https://gist.githubusercontent.com/dvyukov/15639a949278a981c8eb125b3088a6b8/raw/286117bc292578c07c8afbf0fa563cd5528821e7/gistfile1.txt
> 
> Here is one "bad unlock balance detected". The looks well balanced and
> the code path is well exercised:
> https://gist.githubusercontent.com/dvyukov/805f867823b9f77a26c2ebedec5b9b9e/raw/2e6605fb5c90f56ebd1ccda78d613b5c219dfb82/gistfile1.txt
> 
> Here is one "workqueue leaked lock". Again, lock/unlock are very local
> and there is no control flow in between:
> https://gist.githubusercontent.com/dvyukov/4d18d35a79d7e74bf66d6e7ec3794ec0/raw/1ff3e2a5d3a825eb0d196af1f81c67a47fa3a2f6/gistfile1.txt
> 
> Here is one confusing "bad unlock balance detected":
> https://gist.githubusercontent.com/dvyukov/e222fa34e04104678c52a5b5b1ad15a3/raw/943c6ebbc022418b89fa63b6282fa1f1f40a276a/gistfile1.txt
> 
> Here is one confusing "suspicious RCU usage":
> https://gist.githubusercontent.com/dvyukov/77b0ec246e1db86e549a80e4a11ec218/raw/0bce97be186c0a6617d8835a694443ed1aa2a98a/gistfile1.txt
> 
> Overall I have more than 50 of these now.

I'm not aware of any lockdep issues specific to arm64. Mark -- do any of
these look familiar to you when you run syzkaller on real hardware?

Will