On Thu, Jan 21, 2021 at 01:43:14PM -0800, Paul E. McKenney wrote:
On Thu, Jan 21, 2021 at 09:31:10PM +0000, Will Deacon wrote:
On Thu, Jan 21, 2021 at 10:55:21AM -0800, Paul E. McKenney wrote:
On Thu, Jan 21, 2021 at 10:37:21PM +0530, Naresh Kamboju wrote:
While running rcu-torture test on qemu_arm64 and arm64 Juno-r2 device the following kernel crash noticed. This started happening from Linux next next-20210111 tag to next-20210121.
metadata: git branch: master git repo: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next git describe: next-20210111 kernel-config: https://builds.tuxbuild.com/1muTTn7AfqcWvH5x2Alxifn7EUH/config
output log:
[ 621.538050] mem_dump_obj() slab test: rcu_torture_stats = ffff0000c0a3ac40, &rhp = ffff800012debe40, rhp = ffff0000c8cba000, &z = ffff8000091ab8e0 [ 621.546662] mem_dump_obj(ZERO_SIZE_PTR): [ 621.546696] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
[...]
Huh. I am relying on virt_addr_valid() rejecting NULL pointers and things like ZERO_SIZE_PTR, which is defined as ((void *)16). It looks like your configuration rejects NULL as an invalid virtual address, but does not reject ZERO_SIZE_PTR. Is this the intent, given that you are not allowed to dereference a ZERO_SIZE_PTR?
Adding the ARM64 guys on CC for their thoughts.
Spooky timing, there was a thread _today_ about that:
https://lore.kernel.org/r/ecbc7651-82c4-6518-d4a9-dbdbdf833b5b@arm.com
Very good, then my workaround (shown below for Naresh's ease of testing) is only a short-term workaround. Yay! ;-)
Hopefully, though we might need to check other architectures beyond arm64, ppc, and x86, to be certain!
Is there any other latent use of virt_addr_valid() that needs this semantic? If so we'll probably want to backport the changes to arm64's implementation, at least for v5.10.
Vincenzo, would you mind taking a look?
Thanks, Mark.