BPF crash with 3.18-rc1 on arm64 Juno hardware

[Z Lim]

Hi Andre,

On Thu, Oct 23, 2014 at 10:00 AM, Andre Przywara <andre.przywara at arm.com> wrote:
> Hi,
>
> I see a crash with 3.18-rc1 on a Juno board related to bpf_jit (see dump
> below). Userland tries to carry on afterwards, but eventually hangs in
> RCU stalls.
> The kernel has just CONFIG_BPF_JIT enabled, I guess Ubuntu enables this
> automatically if detected.
>

When net-next and arm64-next merged in mainline, a silent failure is
introduced due to new enhancements in net/bpf.
This was actually uncovered before 3.18 merge window, and Daniel's
patch to fix this was discussed here [1].
I see that Catalin has queued up this patch in fixes/core [2].

[1] https://lkml.org/lkml/2014/9/16/73
[2] https://git.kernel.org/cgit/linux/kernel/git/arm64/linux.git/commit/?h=fixes/core&id=b569c1c622c5e60c960a6ae5bd0880e0cdbd56b1)

> The backtrace doesn't make too much sense to me:
>
> void bpf_jit_free(struct bpf_prog *prog)
> {
>         if (prog->jited)
>                 module_free(NULL, prog->bpf_func);
>
>         kfree(prog);
> }
> It crashes in kfree, but has survived the dereference before.
>
> I have no clue about BPF, so if anyone could help me debug this, I'd be
> grateful.
>
> Cheers,
> Andre.
>
>
>  * Starting Signal sysvinit that local filesystems are mounted   [ OK ]
>  * Starting configure network device security                    [ OK ]
> Unable to handle kernel paging request at virtual address 37fffbd21c02290
> pgd = ffffffc976538000
> [37fffbd21c02290] *pgd=0000000000000000, *pud=0000000000000000
> Internal error: Oops: 96000004 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 3 PID: 737 Comm: kworker/3:1 Not tainted 3.18.0-rc1+ #1666
> Workqueue: events bpf_prog_free_deferred
> task: ffffffc977a89580 ti: ffffffc976494000 task.ti: ffffffc976494000
> PC is at kfree+0x70/0x260
> LR is at bpf_jit_free+0x34/0x40
> pc : [<ffffffc0001b0634>] lr : [<ffffffc000099290>] pstate: a0000145
> sp : ffffffc976497ca0
> x29: ffffffc976497ca0 x28: 0000000000000000
> x27: ffffffc97feff400 x26: ffffffc0009b0000
> x25: 0000000000000000 x24: 0000000000000000
> x23: ffffffc97ff03900 x22: ffffffc97feff400
> x21: ffffffc000099290 x20: ffffff800009e000
> x19: ffffff800009e000 x18: 0000007feb492820
> x17: 0000007fb71c6980 x16: ffffffc0001fcc14
> x15: 003b9aca00000000 x14: 0027947614000000
> x13: ffffffffabb6d0e3 x12: 0000000000000018
> x11: 0000000033c2a168 x10: 0000000000000006
> x9 : ffffffc976497bd0 x8 : ffffffc977a89a90
> x7 : ffffffc97736c4d0 x6 : 00000000000009be
> x5 : 0000000000000000 x4 : 0000000000000001
> x3 : ffffffc97feff7c0 x2 : 03ffffff02002780
> x1 : 037fffff21c02290 x0 : ffffffbe00000000
>
> Process kworker/3:1 (pid: 737, stack limit = 0xffffffc976494058)
> Stack: (0xffffffc976497ca0 to 0xffffffc976498000)
> ....