On Thu, 14 Sep 2017 02:50:35 +0530
"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> KPROBES_SANITY_TEST throws the below splat when CONFIG_PREEMPT is
> enabled:
>
> [ 3.140410] Kprobe smoke test: started
> [ 3.149680] DEBUG_LOCKS_WARN_ON(val > preempt_count())
> [ 3.149684] ------------[ cut here ]------------
> [ 3.149695] WARNING: CPU: 19 PID: 1 at kernel/sched/core.c:3094
> preempt_count_sub+0xcc/0x140
> [ 3.149699] Modules linked in:
> [ 3.149705] CPU: 19 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc7-nnr+ #97
> [ 3.149709] task: c0000000fea80000 task.stack: c0000000feb00000
> [ 3.149713] NIP: c00000000011d3dc LR: c00000000011d3d8 CTR:
> c000000000a090d0
> [ 3.149718] REGS: c0000000feb03400 TRAP: 0700 Not tainted
> (4.13.0-rc7-nnr+)
> [ 3.149722] MSR: 8000000000021033 <SF,ME,IR,DR,RI,LE> CR: 28000282 XER:
> 00000000
> [ 3.149732] CFAR: c00000000015aa18 SOFTE: 0
> <snip>
> [ 3.149786] NIP [c00000000011d3dc] preempt_count_sub+0xcc/0x140
> [ 3.149790] LR [c00000000011d3d8] preempt_count_sub+0xc8/0x140
> [ 3.149794] Call Trace:
> [ 3.149798] [c0000000feb03680] [c00000000011d3d8]
> preempt_count_sub+0xc8/0x140 (unreliable)
> [ 3.149804] [c0000000feb036e0] [c000000000046198]
> kprobe_handler+0x228/0x4b0
> [ 3.149810] [c0000000feb03750] [c0000000000269c8]
> program_check_exception+0x58/0x3b0
> [ 3.149816] [c0000000feb037c0] [c00000000000903c]
> program_check_common+0x16c/0x170
> [ 3.149822] --- interrupt: 0 at kprobe_target+0x8/0x20
> LR = init_test_probes+0x248/0x7d0
> [ 3.149829] [c0000000feb03ab0] [c000000000e4f048] kp+0x0/0x80 (unreliable)
> [ 3.149835] [c0000000feb03b10] [c00000000004ea60]
> livepatch_handler+0x38/0x74
> [ 3.149841] [c0000000feb03ba0] [c000000000d0de54] init_kprobes+0x1d8/0x208
> [ 3.149846] [c0000000feb03c40] [c00000000000daa8]
> do_one_initcall+0x68/0x1d0
> [ 3.149852] [c0000000feb03d00] [c000000000ce44f0]
> kernel_init_freeable+0x298/0x374
> [ 3.149857] [c0000000feb03dc0] [c00000000000dd84] kernel_init+0x24/0x160
> [ 3.149863] [c0000000feb03e30] [c00000000000bfec]
> ret_from_kernel_thread+0x5c/0x70
> [ 3.149867] Instruction dump:
> [ 3.149871] 419effdc 3d22001b 39299240 81290000 2f890000 409effc8 3c82ffcb
> 3c62ffcb
> [ 3.149879] 3884bc68 3863bc18 4803d5fd 60000000 <0fe00000> 4bffffa8
> 60000000 60000000
> [ 3.149890] ---[ end trace 432dd46b4ce3d29f ]---
> [ 3.166003] Kprobe smoke test: passed successfully
>
> The issue is that we aren't disabling preemption in
> kprobe_ftrace_handler(). Disable it.
Oops, right! Similar patch may need for x86 too.
Acked-by: Masami Hiramatsu <mhira...@kernel.org>
Thanks!
> Fixes: ead514d5fb30a0 ("powerpc/kprobes: Add support for KPROBES_ON_FTRACE")
> Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/kprobes-ftrace.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kprobes-ftrace.c
> b/arch/powerpc/kernel/kprobes-ftrace.c
> index 6c089d9757c9..2d81404f818c 100644
> --- a/arch/powerpc/kernel/kprobes-ftrace.c
> +++ b/arch/powerpc/kernel/kprobes-ftrace.c
> @@ -65,6 +65,7 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long
> parent_nip,
> /* Disable irq for emulating a breakpoint and avoiding preempt */
> local_irq_save(flags);
> hard_irq_disable();
> + preempt_disable();
>
> p = get_kprobe((kprobe_opcode_t *)nip);
> if (unlikely(!p) || kprobe_disabled(p))
> @@ -86,12 +87,18 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned
> long parent_nip,
> kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> if (!p->pre_handler || !p->pre_handler(p, regs))
> __skip_singlestep(p, regs, kcb, orig_nip);
> - /*
> - * If pre_handler returns !0, it sets regs->nip and
> - * resets current kprobe.
> - */
> + else {
> + /*
> + * If pre_handler returns !0, it sets regs->nip and
> + * resets current kprobe. In this case, we still need
> + * to restore irq, but not preemption.
> + */
> + local_irq_restore(flags);
> + return;
> + }
> }
> end:
> + preempt_enable_no_resched();
> local_irq_restore(flags);
> }
> NOKPROBE_SYMBOL(kprobe_ftrace_handler);
> --
> 2.14.1
>
--
Masami Hiramatsu <mhira...@kernel.org>
