On 1/22/21 10:02 AM, Mark Rutland wrote: > 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! > Which other architectures do you propose to verify? > 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? > I am happy to have a look at it, but due to previous commitments I will be able to get at it after -rc1. A quick grep shows that there are ~32 cases that might be affected by the same semantic in the common code (left out arch/ and drivers/). I will post the improvement for arm64 in the meantime though. > Thanks, > Mark. > -- Regards, Vincenzo
