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! ;-) Thanx, Paul ------------------------------------------------------------------------ diff --git a/mm/slab_common.c b/mm/slab_common.c index cefa9ae..a8375d1 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -550,7 +550,8 @@ bool kmem_valid_obj(void *object) { struct page *page; - if (!virt_addr_valid(object)) + /* Some arches consider ZERO_SIZE_PTR to be a valid address. */ + if (object < (void *)PAGE_SIZE || !virt_addr_valid(object)) return false; page = virt_to_head_page(object); return PageSlab(page);
