From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <naveen.n.rao@linux.vnet.ibm.com>
Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com
 [148.163.156.1])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (No client certificate requested)
 by lists.ozlabs.org (Postfix) with ESMTPS id 3xtF8B1bG4zDqYQ
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 14 Sep 2017 20:27:06 +1000 (AEST)
Received: from pps.filterd (m0098394.ppops.net [127.0.0.1])
 by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id
 v8EAPUma138297
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 14 Sep 2017 06:27:03 -0400
Received: from e23smtp06.au.ibm.com (e23smtp06.au.ibm.com [202.81.31.148])
 by mx0a-001b2d01.pphosted.com with ESMTP id 2cyh1cvw03-1
 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT)
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 14 Sep 2017 06:27:02 -0400
Received: from localhost
 by e23smtp06.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only!
 Violators will be prosecuted
 for <linuxppc-dev@lists.ozlabs.org> from <naveen.n.rao@linux.vnet.ibm.com>;
 Thu, 14 Sep 2017 20:27:00 +1000
Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139])
 by d23relay07.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id
 v8EAPhrX30539854
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 14 Sep 2017 20:25:43 +1000
Received: from d23av04.au.ibm.com (localhost [127.0.0.1])
 by d23av04.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id
 v8EAPiMj004488
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 14 Sep 2017 20:25:45 +1000
Date: Thu, 14 Sep 2017 15:55:39 +0530
From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org,
 Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
 Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Subject: Re: [PATCH 4/5] powerpc/jprobes: Disable preemption when triggered
 through ftrace
References: <2bc413d679c563d3ee338c318066777318577ab2.1505336870.git.naveen.n.rao@linux.vnet.ibm.com>
 <12e85578f8c036d31a0c2197a8956cdb7e0f945b.1505336870.git.naveen.n.rao@linux.vnet.ibm.com>
 <20170913170549.00b607d35f9c754d4d2ca027@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <20170913170549.00b607d35f9c754d4d2ca027@kernel.org>
Message-Id: <20170914102539.3hnz3gtx5my4qm6g@naverao1-tp.localdomain>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

On 2017/09/13 05:05PM, Masami Hiramatsu wrote:
> On Thu, 14 Sep 2017 02:50:35 +0530
> "Naveen N. Rao" <naveen.n.rao@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.

Indeed, I will send a patch for that.

On a related note, I've been looking into why we have !PREEMPT for 
CONFIG_OPTPROBES. It looks like the primary reason is x86 having to deal 
with replacing multiple instructions. However, that isn't true with arm 
and powerpc. So, does it make sense to move 'depends on !PREEMPT' to the 
x86 code? Are there other scenarios where it might cause issues for 
arm/powerpc?

Thanks!
- Naveen