From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9B5C4C433DF for ; Fri, 19 Jun 2020 15:35:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 77EBF206FA for ; Fri, 19 Jun 2020 15:35:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592580926; bh=maaYENQJ8ZL0EP/jDZtR5Sg7D2VvDgzl8nJ0dHfmwGM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=XqCpdP8An+yTBKec9FWpWbcND9Z8SByW/MswYYh+kOa8qFgYAIjpzoW/CQVyQSeHH 9VSWOPbe+meuhOQUJS2TwXfg5OsdsjCLR3AwfZc3yJ81HxHoIeVkZEZcwztUjpdPSq ZVqXzvt8aYpdJlHSi/9jRPK+uJtCVoAJEgRDdCvs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404791AbgFSPfZ (ORCPT ); Fri, 19 Jun 2020 11:35:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:38486 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393535AbgFSPfO (ORCPT ); Fri, 19 Jun 2020 11:35:14 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1772D2166E; Fri, 19 Jun 2020 15:35:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592580914; bh=maaYENQJ8ZL0EP/jDZtR5Sg7D2VvDgzl8nJ0dHfmwGM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=QKFkMf6CmSPcqyw5qJm923cZaKitao9xyRits+mLT1o5loUnNh9K3nPqJkQc3Eopa vbf0NKpPB7Oqt6MXd5rtg+oOe9i4+XnBk2Z9AzigcDiUgFhM4RAoKOeSoCqYwuED/K 92nB46mQZbrh6THXGBQS7WhYLNzuQLqRWfR6wW/I= Date: Sat, 20 Jun 2020 00:35:09 +0900 From: Masami Hiramatsu To: Ming Lei Cc: Steven Rostedt , Masami Hiramatsu , Ming Lei , "Naveen N. Rao" , Anil S Keshavamurthy , Linux Kernel Mailing List , "David S. Miller" , linux-block Subject: Re: kprobe: __blkdev_put probe is missed Message-Id: <20200620003509.9521053fbd384f4f5d23408f@kernel.org> In-Reply-To: <20200619133240.GA351476@T590> References: <20200618125438.GA191266@T590> <20200618225602.3f2cca3f0ed48427fc0a483b@kernel.org> <20200618231901.GA196099@T590> <20200619141239.56f6dda0976453b790190ff7@kernel.org> <20200619072859.GA205278@T590> <20200619081954.3d72a252@oasis.local.home> <20200619133240.GA351476@T590> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Ming, On Fri, 19 Jun 2020 21:32:40 +0800 Ming Lei wrote: > On Fri, Jun 19, 2020 at 08:19:54AM -0400, Steven Rostedt wrote: > > On Fri, 19 Jun 2020 15:28:59 +0800 > > Ming Lei wrote: > > > > > > > > > > OK, then let's make events (for sure) > > > > > > > > root@devnote2:/sys/kernel/debug/tracing# echo p __blkdev_put >> kprobe_events > > > > root@devnote2:/sys/kernel/debug/tracing# echo r __blkdev_put >> kprobe_events > > > > root@devnote2:/sys/kernel/debug/tracing# echo p blkdev_put >> kprobe_events > > > > Hi Ming, > > > > Do you have the kprobe_events file? > > > > > > root@devnote2:/sys/kernel/debug/tracing# echo 1 > events/kprobes/enable > > > > > > I can't find 'events/kprobes' in my VM with upstream kernel, also not found > > > the dir under fedora31(5.5.15-200) & rhel8(v4.18 based). > > > > The events/kprobes directly will be created when you create a > > kprobe_event. It wont exist until then. > > Hi Steven and Masami, > > Got it, thanks for your help, now I can run the test, follows the steps > and results, and there is still one __blkdev_put probed. Hmm, strange... > And it is observed in my VM reliably with 5.7+ or Fedora kernel reliably, > kernel config is attached. Thanks for sharing it. > > [root@ktest-01 tracing]# uname -a > Linux ktest-01 5.7.0+ #1900 SMP Fri Jun 19 16:26:47 CST 2020 x86_64 x86_64 x86_64 GNU/Linux > [root@ktest-01 tracing]# > [root@ktest-01 tracing]# cat kprobe_events > [root@ktest-01 tracing]# > [root@ktest-01 tracing]# echo p blkdev_put >> kprobe_events > [root@ktest-01 tracing]# echo p __blkdev_put >> kprobe_events > [root@ktest-01 tracing]# echo r __blkdev_put >> kprobe_events > [root@ktest-01 tracing]# > [root@ktest-01 tracing]# echo 1 > events/kprobes/enable > [root@ktest-01 tracing]# blockdev --getbsz /dev/sda1 > 4096 > [root@ktest-01 tracing]# echo 0 > events/kprobes/enable > [root@ktest-01 tracing]# cat trace > # tracer: nop > # > # entries-in-buffer/entries-written: 3/3 #P:8 > # > # _-----=> irqs-off > # / _----=> need-resched > # | / _---=> hardirq/softirq > # || / _--=> preempt-depth > # ||| / delay > # TASK-PID CPU# |||| TIMESTAMP FUNCTION > # | | | |||| | | > blockdev-970 [005] .... 17603.447236: p_blkdev_put_0: (blkdev_put+0x0/0xb4) > blockdev-970 [005] .... 17603.447244: p___blkdev_put_0: (__blkdev_put+0x0/0x19d) > blockdev-970 [005] d... 17603.447251: r___blkdev_put_0: (blkdev_close+0x22/0x25 <- __blkdev_put) This shows __blkdev_put() is a tail-call. It is possible that the internal (nested) __blkdev_put() call becomes a goto inside the function by the gcc optimization. Ah, after all it is as expected. With your kconfig, the kernel is very agressively optimized. $ objdump -dS vmlinux | less ... ffffffff81256dc3 <__blkdev_put>: { ffffffff81256dc3: e8 98 85 df ff callq ffffffff8104f360 <__fentry__> ffffffff81256dc8: 41 57 push %r15 ffffffff81256dca: 41 56 push %r14 ffffffff81256dcc: 41 55 push %r13 ... ffffffff81256f05: 75 02 jne ffffffff81256f09 <__blkdev_put+0x146> struct block_device *victim = NULL; ffffffff81256f07: 31 db xor %ebx,%ebx bdev->bd_contains = NULL; ffffffff81256f09: 48 c7 45 60 00 00 00 movq $0x0,0x60(%rbp) ffffffff81256f10: 00 put_disk_and_module(disk); ffffffff81256f11: 4c 89 f7 mov %r14,%rdi ffffffff81256f14: e8 c6 3d 11 00 callq ffffffff8136acdf mutex_unlock(&bdev->bd_mutex); ffffffff81256f19: 4c 89 ff mov %r15,%rdi __blkdev_put(victim, mode, 1); ffffffff81256f1c: 41 bc 01 00 00 00 mov $0x1,%r12d mutex_unlock(&bdev->bd_mutex); ffffffff81256f22: e8 8d d7 48 00 callq ffffffff816e46b4 bdput(bdev); ffffffff81256f27: 48 89 ef mov %rbp,%rdi ffffffff81256f2a: e8 f0 e9 ff ff callq ffffffff8125591f if (victim) ffffffff81256f2f: 48 85 db test %rbx,%rbx ffffffff81256f32: 74 08 je ffffffff81256f3c <__blkdev_put+0x179> ffffffff81256f34: 48 89 dd mov %rbx,%rbp ffffffff81256f37: e9 b4 fe ff ff jmpq ffffffff81256df0 <__blkdev_put+0x2d> <<-----THIS!! } ffffffff81256f3c: 48 8b 44 24 28 mov 0x28(%rsp),%rax ffffffff81256f41: 65 48 33 04 25 28 00 xor %gs:0x28,%rax ffffffff81256f48: 00 00 ffffffff81256f4a: 74 05 je ffffffff81256f51 <__blkdev_put+0x18e> ffffffff81256f4c: e8 5a 4e 48 00 callq ffffffff816dbdab <__stack_chk_fail> ffffffff81256f51: 48 83 c4 30 add $0x30,%rsp ffffffff81256f55: 5b pop %rbx ffffffff81256f56: 5d pop %rbp ffffffff81256f57: 41 5c pop %r12 ffffffff81256f59: 41 5d pop %r13 ffffffff81256f5b: 41 5e pop %r14 ffffffff81256f5d: 41 5f pop %r15 ffffffff81256f5f: c3 retq As you can see, the nested __blkdev_put() is coverted to a loop. If you put kprobe on __blkdev_put+0x2d, you'll see the event twice. Thank you, -- Masami Hiramatsu