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Subject[PATCH] rcu: Use printk_deferred when holding rtp->cbs_gbl_lock
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There is a lockdep complains about invalid context:

[2.464191] [ BUG: Invalid wait context ]
[2.464192] 5.17.0-rc8-43124-gf8d61731923c #75 Not tainted
[2.464193] -----------------------------
[2.464193] swapper/0/1 is trying to lock:
[2.464194] ffffffff846e8c38 (&port_lock_key){....}-{3:3}, at: serial8250_console_write+0x2b0/0x320
[2.464202] other info that might help us debug this:
[2.464202] context-{5:5}
[2.464203] 3 locks held by swapper/0/1:
[2.464204] #0: ffffffff82b77f08 (rcu_tasks.cbs_gbl_lock){....}-{2:2}, at: cblist_init_generic+0x26/0x2a0
[2.464211] #1: ffffffff82b74540 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0xb5/0x2a0
[2.464217] #2: ffffffff82a94320 (console_owner){....}-{0:0}, at: console_unlock+0x18a/0x5f0
[2.464221] stack backtrace:
...
[2.464266] _printk+0x52/0x6e
[2.464271] cblist_init_generic+0x25a/0x2a0
[2.464277] rcu_init_tasks_generic+0x21/0xe1
[2.464280] kernel_init_freeable+0x156/0x324
[2.464285] kernel_init+0x17/0x150
[2.464288] ret_from_fork+0x22/0x30
[2.464293] </TASK>

At cblist_init_generic() and rcu_tasks_need_gpcb(),
After taking rtp->cbs_gbl_lock(raw spinlock), at cblist_init_generic()
and rcu_tasks_need_gpcb(), we print some logs and will attempt to
acquire a spinlock(port_lock_key). Since spin_lock() can sleep
with PREEMPT_RT, it is illegal that attempt to acquire spinlocks
inside raw_spinlocks.

This patch tries to avoid this issue by using printk_deferred().

Fixes: ab97152f88a4 ("rcu-tasks: Use more callback queues if contention encountered")
Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
---
kernel/rcu/tasks.h | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index d64f0b1d8cd3..98249e6a1054 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -222,7 +222,8 @@ 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__);
+ printk_deferred("%s: Setting adjustable number of callback queues.\n",
+ __func__);
} else if (rcu_task_enqueue_lim == 0) {
rcu_task_enqueue_lim = 1;
}
@@ -305,7 +306,8 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids) + 1);
WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids);
smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids);
- pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name);
+ printk_deferred("Switching %s to per-CPU callback queuing.\n",
+ rtp->name);
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
}
@@ -420,7 +422,8 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids) + 1);
smp_store_release(&rtp->percpu_enqueue_lim, 1);
rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu();
- pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name);
+ printk_deferred("Starting switch %s to CPU-0 callback queuing.\n",
+ rtp->name);
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
}
@@ -429,7 +432,8 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) {
WRITE_ONCE(rtp->percpu_dequeue_lim, 1);
- pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name);
+ printk_deferred("Completing switch %s to CPU-0 callback queuing.\n",
+ rtp->name);
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
}
--
2.18.0.huawei.25
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