This is a note to let you know that I've just added the patch titled
powerpc/jprobes: Disable preemption when triggered through ftrace
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: powerpc-jprobes-disable-preemption-when-triggered-through-ftrace.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 6baea433bc84cd148af1c524389a8d756f67412e Mon Sep 17 00:00:00 2001
From: "Naveen N. Rao" naveen.n.rao@linux.vnet.ibm.com Date: Fri, 22 Sep 2017 14:40:47 +0530 Subject: powerpc/jprobes: Disable preemption when triggered through ftrace
From: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com
commit 6baea433bc84cd148af1c524389a8d756f67412e upstream.
KPROBES_SANITY_TEST throws the below splat when CONFIG_PREEMPT is enabled:
Kprobe smoke test: started DEBUG_LOCKS_WARN_ON(val > preempt_count()) ------------[ cut here ]------------ WARNING: CPU: 19 PID: 1 at kernel/sched/core.c:3094 preempt_count_sub+0xcc/0x140 Modules linked in: CPU: 19 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc7-nnr+ #97 task: c0000000fea80000 task.stack: c0000000feb00000 NIP: c00000000011d3dc LR: c00000000011d3d8 CTR: c000000000a090d0 REGS: c0000000feb03400 TRAP: 0700 Not tainted (4.13.0-rc7-nnr+) MSR: 8000000000021033 <SF,ME,IR,DR,RI,LE> CR: 28000282 XER: 00000000 CFAR: c00000000015aa18 SOFTE: 0 <snip> NIP preempt_count_sub+0xcc/0x140 LR preempt_count_sub+0xc8/0x140 Call Trace: preempt_count_sub+0xc8/0x140 (unreliable) kprobe_handler+0x228/0x4b0 program_check_exception+0x58/0x3b0 program_check_common+0x16c/0x170 --- interrupt: 0 at kprobe_target+0x8/0x20 LR = init_test_probes+0x248/0x7d0 kp+0x0/0x80 (unreliable) livepatch_handler+0x38/0x74 init_kprobes+0x1d8/0x208 do_one_initcall+0x68/0x1d0 kernel_init_freeable+0x298/0x374 kernel_init+0x24/0x160 ret_from_kernel_thread+0x5c/0x70 Instruction dump: 419effdc 3d22001b 39299240 81290000 2f890000 409effc8 3c82ffcb 3c62ffcb 3884bc68 3863bc18 4803d5fd 60000000 <0fe00000> 4bffffa8 60000000 60000000 ---[ end trace 432dd46b4ce3d29f ]--- Kprobe smoke test: passed successfully
The issue is that we aren't disabling preemption in kprobe_ftrace_handler(). Disable it.
Fixes: ead514d5fb30a0 ("powerpc/kprobes: Add support for KPROBES_ON_FTRACE") Acked-by: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com [mpe: Trim oops a little for formatting] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/kprobes-ftrace.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
--- a/arch/powerpc/kernel/kprobes-ftrace.c +++ b/arch/powerpc/kernel/kprobes-ftrace.c @@ -65,6 +65,7 @@ void kprobe_ftrace_handler(unsigned long /* 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 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);
Patches currently in stable-queue which might be from naveen.n.rao@linux.vnet.ibm.com are
queue-4.14/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch queue-4.14/powerpc-kprobes-disable-preemption-before-invoking-probe-handler-for-optprobes.patch queue-4.14/powerpc-jprobes-disable-preemption-when-triggered-through-ftrace.patch