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([2409:8a28:e62:3990:a113:6fc:a7b4:4226]) by smtp.gmail.com with ESMTPSA id u10-20020a63b54a000000b00380ea901cd2sm17584716pgo.6.2022.03.22.09.33.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Mar 2022 09:34:05 -0700 (PDT) Message-ID: <0a7ebd49-cfdd-911e-3982-44f594320b0f@bytedance.com> Date: Wed, 23 Mar 2022 00:33:51 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [External] Re: [PATCH v2 2/6] perf/core: Introduce percpu perf_cgroup Content-Language: en-US To: Peter Zijlstra Cc: mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org, eranian@google.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, duanxiongchun@bytedance.com, songmuchun@bytedance.com References: <20220322120834.98637-1-zhouchengming@bytedance.com> <20220322120834.98637-3-zhouchengming@bytedance.com> From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/3/22 9:01 下午, Peter Zijlstra wrote: > On Tue, Mar 22, 2022 at 08:08:30PM +0800, Chengming Zhou wrote: >> Although we don't have incosistency problem any more, we can >> have other problem like: >> >> CPU1 CPU2 >> (in context_switch) (attach running task) >> prev->cgroups = cgrp2 >> perf_cgroup_sched_switch(prev, next) >> cgrp2 == cgrp2 is True >> > > Again, I'm not following, how can you attach to a running task from > another CPU ? Hi Peter, I make a little testcase which can reproduce the race problem, on system with PSI disabled. Because when PSI enabled, cgroup_move_task() will hold rq lock to assign task->cgroups. ``` #!/bin/bash cd /sys/fs/cgroup/perf_event mkdir cg1 mkdir cg2 perf stat -e cycles --cgroup /cg1 & cg_run() { cg=$1 shift echo $BASHPID > $cg/cgroup.procs $@ } cg_run cg1 schbench -r 100 & cg_run cg2 schbench -r 100 & while true; do for i in $(cat cg1/cgroup.procs); do echo $i > cg2/cgroup.procs done for i in $(cat cg2/cgroup.procs); do echo $i > cg1/cgroup.procs done done ``` Some seconds later, dmesg will show the WARNING message: [ 51.777830] WARNING: CPU: 2 PID: 1849 at kernel/events/core.c:869 perf_cgroup_switch+0x246/0x290 [ 51.779167] Modules linked in: [ 51.779696] CPU: 2 PID: 1849 Comm: schbench Not tainted 5.17.0-rc8 #28 [ 51.780691] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014 [ 51.782353] RIP: 0010:perf_cgroup_switch+0x246/0x290 [ 51.783145] Code: 0f 0b e9 0b ff ff ff 48 83 7c 24 08 00 74 0c e8 00 7e f7 ff fb 66 0f 1f 44 00 00 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <0f> 0b e9 4f fe ff ff e8 be 7e f7 ff e8 a9 1f 93 00 89 c0 49 c7 c5 [ 51.785804] RSP: 0018:ffffba4440fcbd80 EFLAGS: 00010086 [ 51.786617] RAX: 0000000000000002 RBX: ffff8d78eb8b7200 RCX: 0000000000000000 [ 51.787696] RDX: 0000000000000000 RSI: ffffffffae1c83db RDI: ffffffffae185a69 [ 51.788777] RBP: ffff8d78eb8aad40 R08: 0000000000000001 R09: 0000000000000001 [ 51.789854] R10: 0000000000000000 R11: ffff8d78eb8b7220 R12: ffff8d78eb8b7208 [ 51.790929] R13: ffff8d78eb8aafa0 R14: ffff8d74cd6bb600 R15: 0000000000000000 [ 51.792006] FS: 00007fedaaffd700(0000) GS:ffff8d78eb880000(0000) knlGS:0000000000000000 [ 51.793223] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 51.794122] CR2: 000055e4bf2b696c CR3: 00000001128a2003 CR4: 0000000000370ee0 [ 51.795209] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 51.796292] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 51.797375] Call Trace: [ 51.797828] [ 51.798229] __perf_event_task_sched_in+0x151/0x350 [ 51.799009] ? lock_release+0x1ed/0x2e0 [ 51.799640] finish_task_switch+0x1d3/0x2e0 [ 51.800328] ? __switch_to+0x136/0x4b0 [ 51.800953] __schedule+0x33e/0xae0 [ 51.801535] schedule+0x4e/0xc0 [ 51.802080] exit_to_user_mode_prepare+0x172/0x2a0 [ 51.802850] ? asm_sysvec_apic_timer_interrupt+0xa/0x20 [ 51.803675] irqentry_exit_to_user_mode+0x5/0x40 [ 51.804413] sysvec_apic_timer_interrupt+0x5c/0xd0 [ 51.805183] asm_sysvec_apic_timer_interrupt+0x12/0x20 Thanks.