Hi,
On 9/4/23 20:08, Joel Fernandes (Google) wrote:
> It is unsafe to dump vmalloc area information when trying to do so from
> some contexts. Add a safer trylock version of the same function to do a
> best-effort VMA finding and use it from vmalloc_dump_obj().
I was a bit confused by the subject which suggests a new function is added,
but it seems open-coded in its only caller. I assume it's due to evolution
of the series. Something like:
mm/vmalloc: use trylock for vmap_area_lock in vmalloc_dump_obj()
?
I also notice it's trying hard to copy everything from "vm" to temporary
variables before unlocking, presumably to prevent use-after-free, so should
that be also mentioned in the changelog?
> [applied test robot feedback on unused function fix.]
> [applied Uladzislau feedback on locking.]
>
> Reported-by: Zhen Lei <thunder.leizhen@xxxxxxxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: rcu@xxxxxxxxxxxxxxx
> Cc: Zqiang <qiang.zhang1211@xxxxxxxxx>
> Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> Fixes: 98f180837a89 ("mm: Make mem_dump_obj() handle vmalloc() memory")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> mm/vmalloc.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 93cf99aba335..2c6a0e2ff404 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4274,14 +4274,32 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> #ifdef CONFIG_PRINTK
> bool vmalloc_dump_obj(void *object)
> {
> - struct vm_struct *vm;
> void *objp = (void *)PAGE_ALIGN((unsigned long)object);
> + const void *caller;
> + struct vm_struct *vm;
> + struct vmap_area *va;
> + unsigned long addr;
> + unsigned int nr_pages;
>
> - vm = find_vm_area(objp);
> - if (!vm)
> + if (!spin_trylock(&vmap_area_lock))
> + return false;
> + va = __find_vmap_area((unsigned long)objp, &vmap_area_root);
> + if (!va) {
> + spin_unlock(&vmap_area_lock);
> return false;
> + }
> +
> + vm = va->vm;
> + if (!vm) {
> + spin_unlock(&vmap_area_lock);
> + return false;
> + }
> + addr = (unsigned long)vm->addr;
> + caller = vm->caller;
> + nr_pages = vm->nr_pages;
> + spin_unlock(&vmap_area_lock);
> pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
> - vm->nr_pages, (unsigned long)vm->addr, vm->caller);
> + nr_pages, addr, caller);
> return true;
> }
> #endif
