linux-kernel - [PATCH] printk: Add atomic context check inside console

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Message-ID: <20240222090538.23017-1-quic_mojha@quicinc.com>
Date: Thu, 22 Feb 2024 14:35:38 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: <pmladek@...e.com>, <rostedt@...dmis.org>, <john.ogness@...utronix.de>,
        <senozhatsky@...omium.org>
CC: <linux-kernel@...r.kernel.org>, Mukesh Ojha <quic_mojha@...cinc.com>
Subject: [PATCH] printk: Add atomic context check inside console_unlock()

Situation of schedule while atomic context can happen in a
scenario if CPU-Y executing a async probe of ufs and while
printing a line it is started spinning for console lock
after preemption disable on CPU-Y and later it got the handover
of console lock from CPU-X and in console_unlock() it get
schedule with preempt disable as console_may_schedule was one
and due to which do_cond_resched was one.

         CPU-X                          CPU-Y

                                      worker_thread
                                       process_one_work
                                        async_run_entry_fn
                                         ufshcd_async_scan
                                          ufshcd_device_init
really_probe+0x1c8                         ufshcd_probe_hba
 platform_probe+0xc0                        ufshcd_config_mcq
  qcom_geni_serial_probe+0x374               _dev_info
   uart_add_one_port+0x10                     __dev_printk
    serial_ctrl_register_port+0x10             dev_printk_emit
     serial_core_register_port+0x5dc            dev_vprintk_emit
      register_console+0x284                      vprintk_emit
       console_init_seq()                          preempt_disable();
	                                           console_trylock_spinning()
        console_lock();
         console_flush_all()

Hand over of console lock happen from CPU-X to CPU-Y
                                                   console_unlock()
          console_lock+0x74                         console_flush_all
	   down[jt]+0x40                             __might_resched
	    __down+0x18
             __down_common+0x68
              ___down_common+0xdc
               schedule_timeout+0x4c
                schedule+0x78
                 __schedule+0x6c0

Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
---
 kernel/printk/printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f2444b581e16..8b666feff65d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3028,7 +3028,7 @@ void console_unlock(void)
 	 * messages practically incapacitating the system. Therefore, create
 	 * a local to use for the printing loop.
 	 */
-	do_cond_resched = console_may_schedule;
+	do_cond_resched = in_atomic() || console_may_schedule;
 
 	do {
 		console_may_schedule = 0;
-- 
2.43.0.254.ga26002b62827