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McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki Cc: Jiazi Li , rcu@vger.kernel.org, "mingzhu.wang" Subject: [PATCH] rcu: use NMI to dump backtrace of blkd-task running on other cpu Date: Fri, 17 Apr 2026 09:38:13 +0800 Message-ID: <20260417013816.3653-1-jqqlijiazi@gmail.com> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit sched_show_task cannot dump backtrace of blkd-task running on other cpu: [117421.286553][ C0] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [117421.286579][ C0] rcu: Tasks blocked on level-0 rcu_node (CPUs 0-7): P2280 [117421.286595][ C0] rcu: (detected by 0, t=5252 jiffies, g=751845, q=66318 ncpus=8) [117421.286604][ C0] task:android.imms2 state:R running task stack:0 ... [117421.286617][ C0] Call trace: [117421.286622][ C0] __switch_to+0x1a0/0x318 [117421.286636][ C0] 0x0 So use NMI to dump backtrace: [ 390.584143] rcub/0: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [ 390.585156] rcub/0: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-7): P6816 [ 390.586207] rcub/0: rcu: (detected by 5, t=52532 jiffies, g=7405, q=63942 ncpus=8) [ 390.587320] rcub/0: Sending NMI from CPU 5 to CPUs 4: [ 390.588111] rcu_stall_threa: NMI backtrace for cpu 4 [ 390.588116] rcu_stall_threa: CPU: 4 UID: 0 PID: 6816 Comm: rcu_stall_threa Tainted: P... [ 390.588120] rcu_stall_threa: Tainted: [P]=PROPRIETARY_MODULE, [W]=WARN, [O]=OOT_MODULE [ 390.588122] rcu_stall_threa: Hardware name: MT6858 (DT) [ 390.588123] rcu_stall_threa: pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 390.588125] rcu_stall_threa: pc : _raw_spin_unlock_irqrestore+0x1c/0x44 [ 390.588131] rcu_stall_threa: lr : ___ratelimit+0xd4/0x110 [ 390.588134] rcu_stall_threa: sp : ffffffc08464bdf0 [ 390.588135] rcu_stall_threa: x29: ffffffc08464bdf0 x28: 0000000000000000 x27: 0000000000000000 [ 390.588138] rcu_stall_threa: x26: 0000000000000000 x25: 0000000000000000 x24: 00000000000004e2 [ 390.588140] rcu_stall_threa: x23: ffffffd82ae77000 x22: ffffffd82af1fae8 x21: 000000000000000a [ 390.588142] rcu_stall_threa: x20: 0000000000000000 x19: 0000000000000000 x18: ffffffc08456d020 [ 390.588144] rcu_stall_threa: x17: 000000008c623181 x16: 000000008c623181 x15: 0000000000000010 [ 390.588146] rcu_stall_threa: x14: 0000000000000100 x13: ffffffc084648000 x12: ffffffc08464c000 [ 390.588148] rcu_stall_threa: x11: 5e2da9f91a08d800 x10: ffffffd8299b39fc x9 : 0000000100005874 [ 390.588150] rcu_stall_threa: x8 : 0000000000000000 x7 : 0000000000000001 x6 : fffffffebea2b0a0 [ 390.588152] rcu_stall_threa: x5 : 0000000000000000 x4 : 0000000000000402 x3 : 0000000000000000 [ 390.588154] rcu_stall_threa: x2 : ffffff81ca8d9680 x1 : 0000000000000000 x0 : 0000000000000001 [ 390.588156] rcu_stall_threa: Call trace: [ 390.588157] rcu_stall_threa: _raw_spin_unlock_irqrestore+0x1c/0x44 [ 390.588159] rcu_stall_threa: ___ratelimit+0xd4/0x110 [ 390.588161] rcu_stall_threa: rcu_thread_func+0x90/0xa8 [ 390.588164] rcu_stall_threa: kthread+0x110/0x1a4 [ 390.588167] rcu_stall_threa: ret_from_fork+0x10/0x20 Signed-off-by: Jiazi Li Tested-by: mingzhu.wang --- kernel/rcu/tree_stall.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index b67532cb8770..5806f9a43579 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -289,7 +289,12 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) * Avoid triggering hard lockup. */ touch_nmi_watchdog(); - sched_show_task(t); + if (unlikely(t->on_cpu && t != current) && + trigger_single_cpu_backtrace(task_cpu(t))) { + /*Successfully triggered remote backtrace*/ + } else { + sched_show_task(t); + } } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } -- 2.49.0