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@xxxxxxx > > 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.
