From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (bilbo.ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40D0Zl6d5mzF1w1 for ; Sun, 1 Apr 2018 01:03:43 +1100 (AEDT) In-Reply-To: <20180117122224.19860-1-naveen.n.rao@linux.vnet.ibm.com> To: "Naveen N. Rao" From: Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org Subject: Re: powerpc/kprobes: Fix call trace due to incorrect preempt count Message-Id: <40D0Zl56tgz9s1r@ozlabs.org> Date: Sun, 1 Apr 2018 01:03:43 +1100 (AEDT) List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2018-01-17 at 12:22:24 UTC, "Naveen N. Rao" wrote: > Michael Ellerman reported the following call trace when running > ftracetest: > > BUG: using __this_cpu_write() in preemptible [00000000] code: ftracetest/6178 > caller is opt_pre_handler+0xc4/0x110 > CPU: 1 PID: 6178 Comm: ftracetest Not tainted 4.15.0-rc7-gcc6x-gb2cd1df #1 > Call Trace: > [c0000000f9ec39c0] [c000000000ac4304] dump_stack+0xb4/0x100 (unreliable) > [c0000000f9ec3a00] [c00000000061159c] check_preemption_disabled+0x15c/0x170 > [c0000000f9ec3a90] [c000000000217e84] opt_pre_handler+0xc4/0x110 > [c0000000f9ec3af0] [c00000000004cf68] optimized_callback+0x148/0x170 > [c0000000f9ec3b40] [c00000000004d954] optinsn_slot+0xec/0x10000 > [c0000000f9ec3e30] [c00000000004bae0] kretprobe_trampoline+0x0/0x10 > > This is showing up since OPTPROBES is now enabled with CONFIG_PREEMPT. > > trampoline_probe_handler() considers itself to be a special kprobe > handler for kretprobes. In doing so, it expects to be called from > kprobe_handler() on a trap, and re-enables preemption before returning a > non-zero return value so as to suppress any subsequent processing of the > trap by the kprobe_handler(). > > However, with optprobes, we don't deal with special handlers (we ignore > the return code) and just try to re-enable preemption causing the above > trace. > > To address this, modify trampoline_probe_handler() to not be special. > The only additional processing done in kprobe_handler() is to emulate > the instruction (in this case, a 'nop'). We adjust the value of > regs->nip for the purpose and delegate the job of re-enabling > preemption and resetting current kprobe to the probe handlers > (kprobe_handler() or optimized_callback()). > > Reported-by: Michael Ellerman > Signed-off-by: Naveen N. Rao > Acked-by: Ananth N Mavinakayanahalli Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/e6e133c47e6bd4d5dac05b35d06634 cheers