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SubjectRe: [PATCH] rcu-tasks: Avoid pr_info() with spin lock in cblist_init_generic()
On Wed, Aug 03, 2022 at 01:22:05AM +0900, Shigeru Yoshida wrote:
> pr_info() is called with rtp->cbs_gbl_lock spin lock locked. Because
> pr_info() calls printk() that might sleep, this will result in BUG
> like below:
>
> [ 0.206455] cblist_init_generic: Setting adjustable number of callback queues.
> [ 0.206463]
> [ 0.206464] =============================
> [ 0.206464] [ BUG: Invalid wait context ]
> [ 0.206465] 5.19.0-00428-g9de1f9c8ca51 #5 Not tainted
> [ 0.206466] -----------------------------
> [ 0.206466] swapper/0/1 is trying to lock:
> [ 0.206467] ffffffffa0167a58 (&port_lock_key){....}-{3:3}, at: serial8250_console_write+0x327/0x4a0
> [ 0.206473] other info that might help us debug this:
> [ 0.206473] context-{5:5}
> [ 0.206474] 3 locks held by swapper/0/1:
> [ 0.206474] #0: ffffffff9eb597e0 (rcu_tasks.cbs_gbl_lock){....}-{2:2}, at: cblist_init_generic.constprop.0+0x14/0x1f0
> [ 0.206478] #1: ffffffff9eb579c0 (console_lock){+.+.}-{0:0}, at: _printk+0x63/0x7e
> [ 0.206482] #2: ffffffff9ea77780 (console_owner){....}-{0:0}, at: console_emit_next_record.constprop.0+0x111/0x330
> [ 0.206485] stack backtrace:
> [ 0.206486] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-00428-g9de1f9c8ca51 #5
> [ 0.206488] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014
> [ 0.206489] Call Trace:
> [ 0.206490] <TASK>
> [ 0.206491] dump_stack_lvl+0x6a/0x9f
> [ 0.206493] __lock_acquire.cold+0x2d7/0x2fe
> [ 0.206496] ? stack_trace_save+0x46/0x70
> [ 0.206497] lock_acquire+0xd1/0x2f0
> [ 0.206499] ? serial8250_console_write+0x327/0x4a0
> [ 0.206500] ? __lock_acquire+0x5c7/0x2720
> [ 0.206502] _raw_spin_lock_irqsave+0x3d/0x90
> [ 0.206504] ? serial8250_console_write+0x327/0x4a0
> [ 0.206506] serial8250_console_write+0x327/0x4a0
> [ 0.206508] console_emit_next_record.constprop.0+0x180/0x330
> [ 0.206511] console_unlock+0xf7/0x1f0
> [ 0.206512] vprintk_emit+0xf7/0x330
> [ 0.206514] _printk+0x63/0x7e
> [ 0.206516] cblist_init_generic.constprop.0.cold+0x24/0x32
> [ 0.206518] rcu_init_tasks_generic+0x5/0xd9
> [ 0.206522] kernel_init_freeable+0x15b/0x2a2
> [ 0.206523] ? rest_init+0x160/0x160
> [ 0.206526] kernel_init+0x11/0x120
> [ 0.206527] ret_from_fork+0x1f/0x30
> [ 0.206530] </TASK>
> [ 0.207018] cblist_init_generic: Setting shift to 1 and lim to 1.
>
> This patch moves pr_info() so that it is called without
> rtp->cbs_gbl_lock locked.
>
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>

This patch looks good, except that wasn't this supposed to be fixed
in printk()? Or am I suffering from wishful thinking?

Thanx, Paul

> ---
> kernel/rcu/tasks.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index 3925e32159b5..d46dd970bf22 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -227,7 +227,6 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
> if (rcu_task_enqueue_lim < 0) {
> rcu_task_enqueue_lim = 1;
> rcu_task_cb_adjust = true;
> - pr_info("%s: Setting adjustable number of callback queues.\n", __func__);
> } else if (rcu_task_enqueue_lim == 0) {
> rcu_task_enqueue_lim = 1;
> }
> @@ -256,6 +255,10 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
> raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
> }
> raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
> +
> + if (rcu_task_cb_adjust)
> + pr_info("%s: Setting adjustable number of callback queues.\n", __func__);
> +
> pr_info("%s: Setting shift to %d and lim to %d.\n", __func__, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim));
> }
>
> --
> 2.37.1
>

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