Re: [syzbot] [block?] [mm?] INFO: rcu detected stall in wb_workfn (4)

[Hillf Danton <hdanton@sina.com>]

> Date: Tue, 02 Sep 2025 07:41:28 -0700	[thread overview]
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    b320789d6883 Linux 6.17-rc4
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1406ae62580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
> dashboard link: https://syzkaller.appspot.com/bug?extid=5b4f4f81240931b16844
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=133b5e34580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1639ca42580000

#syz test upstream master

--- x/kernel/rcu/tree_stall.h
+++ y/kernel/rcu/tree_stall.h
@@ -590,8 +590,15 @@ static void rcu_check_gp_kthread_starvat
 			if (cpu_is_offline(cpu)) {
 				pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
 			} else if (!(data_race(READ_ONCE(rdp->mynode->qsmask)) & rdp->grpmask)) {
+				int i;
 				pr_err("Stack dump where RCU GP kthread last ran:\n");
 				dump_cpu_task(cpu);
+				for_each_online_cpu(i) {
+					if (i == cpu)
+						continue;
+					pr_err("Stack dump on CPU%d\n", i);
+					dump_cpu_task(i);
+				}
 			}
 			wake_up_process(gpk);
 		}
--