On Tue, Sep 15, 2020 at 5:58 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Tue, Sep 15, 2020 at 5:44 PM Yonghong Song <yhs@xxxxxx> wrote:
> >
> > Running selftest
> > ./btf_btf -p
> > the kernel had the following warning:
> > [ 51.528185] WARNING: CPU: 3 PID: 1756 at kernel/bpf/hashtab.c:717 htab_map_get_next_key+0x2eb/0x300
> > [ 51.529217] Modules linked in:
> > [ 51.529583] CPU: 3 PID: 1756 Comm: test_btf Not tainted 5.9.0-rc1+ #878
> > [ 51.530346] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.el7.centos 04/01/2014
> > [ 51.531410] RIP: 0010:htab_map_get_next_key+0x2eb/0x300
> > ...
> > [ 51.542826] Call Trace:
> > [ 51.543119] map_seq_next+0x53/0x80
> > [ 51.543528] seq_read+0x263/0x400
> > [ 51.543932] vfs_read+0xad/0x1c0
> > [ 51.544311] ksys_read+0x5f/0xe0
> > [ 51.544689] do_syscall_64+0x33/0x40
> > [ 51.545116] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > The related source code in kernel/bpf/hashtab.c:
> > 709 static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
> > 710 {
> > 711 struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
> > 712 struct hlist_nulls_head *head;
> > 713 struct htab_elem *l, *next_l;
> > 714 u32 hash, key_size;
> > 715 int i = 0;
> > 716
> > 717 WARN_ON_ONCE(!rcu_read_lock_held());
> >
> > In kernel/bpf/inode.c, bpffs map pretty print calls map->ops->map_get_next_key()
> > without holding a rcu_read_lock(), hence causing the above warning.
> > To fix the issue, just surrounding map->ops->map_get_next_key() with rcu read lock.
> >
> > Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Cc: Andrii Nakryiko <andriin@xxxxxx>
> > Cc: Martin KaFai Lau <kafai@xxxxxx>
> > Fixes: a26ca7c982cb ("bpf: btf: Add pretty print support to the basic arraymap")
> > Signed-off-by: Yonghong Song <yhs@xxxxxx>
> > ---
>
> LGTM.
>
> Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Applied. Thanks!
