This is a note to let you know that I've just added the patch titled
rcu: Fix to include first blocked task in stall warning
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-fix-to-include-first-blocked-task-in-stall-warni.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit e37c0b6edf2b0a5b7fc19debac2349fad8dd9674
Author: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
Date: Sun May 16 00:45:11 2021 +0800
rcu: Fix to include first blocked task in stall warning
[ Upstream commit e6a901a44f76878ed1653626c9ff4cfc5a3f58f8 ]
The for loop in rcu_print_task_stall() always omits ts[0], which points
to the first task blocking the stalled grace period. This in turn fails
to count this first task, which means that ndetected will be equal to
zero when all CPUs have passed through their quiescent states and only
one task is blocking the stalled grace period. This zero value for
ndetected will in turn result in an incorrect "All QSes seen" message:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-1 rcu_node (CPUs 12-23):
(detected by 15, t=6504 jiffies, g=164777, q=9011209)
rcu: All QSes seen, last rcu_preempt kthread activity 1 (4295252379-4295252378), jiffies_till_next_fqs=1, root ->qsmask 0x2
BUG: sleeping function called from invalid context at include/linux/uaccess.h:156
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 70613, name: msgstress04
INFO: lockdep is turned off.
Preemption disabled at:
[<ffff8000104031a4>] create_object.isra.0+0x204/0x4b0
CPU: 15 PID: 70613 Comm: msgstress04 Kdump: loaded Not tainted
5.12.2-yoctodev-standard #1
Hardware name: Marvell OcteonTX CN96XX board (DT)
Call trace:
dump_backtrace+0x0/0x2cc
show_stack+0x24/0x30
dump_stack+0x110/0x188
___might_sleep+0x214/0x2d0
__might_sleep+0x7c/0xe0
This commit therefore fixes the loop to include ts[0].
Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled")
Tested-by: Qais Yousef <qais.yousef@xxxxxxx>
Signed-off-by: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 3d11155e0033..d56b4ede1db3 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -282,8 +282,8 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
break;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- for (i--; i; i--) {
- t = ts[i];
+ while (i) {
+ t = ts[--i];
if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr))
pr_cont(" P%d", t->pid);
else
