On Wed, Dec 9, 2020 at 6:44 PM Toke Høiland-Jørgensen <t...@redhat.com> wrote: > > Zhu Yanjun <zyjzyj2...@gmail.com> writes: > > > On Wed, Dec 9, 2020 at 1:12 AM Daniel Borkmann <dan...@iogearbox.net> wrote: > >> > >> On 12/9/20 6:03 AM, Zhu Yanjun wrote: > >> > In the function xdp_umem_pin_pages, if npgs != umem->npgs and > >> > npgs >= 0, the function xdp_umem_unpin_pages is called. In this > >> > function, kfree is called to handle umem->pgs, and then in the > >> > function xdp_umem_pin_pages, kfree is called again to handle > >> > umem->pgs. Eventually, umem->pgs is freed twice. > >> > > >> > Acked-by: Björn Töpel <bjorn.to...@intel.com> > >> > Signed-off-by: Zhu Yanjun <yanjun....@intel.com> > >> > >> Please also fix up the commit log according to Bjorn's prior feedback [0]. > >> If it's just a cleanup, it should state so, the commit message right now > >> makes it sound like an actual double free bug. > > > > The umem->pgs is actually freed twice. Since umem->pgs is set to NULL > > after the first kfree, > > the second kfree would not trigger call trace. > > IMO, the commit log is very clear about this. > > Yes, it is very clear; and also wrong. As someone already pointed out, > passing a NULL pointer to kfree() doesn't actually lead to a double > free:
In your commit, does "double free" mean the call trace bug? If so, I will correct it in my commit log. In my commit log, I just mean that kfree is called twice. And the second kfree is meaningless. And since NULL is passed to it, this will not trigger "double free" CallTrace. I will send the latest version soon. Zhu Yanjun > > https://elixir.bootlin.com/linux/latest/source/mm/slub.c#L4106 > > -Toke >
