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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	John Kacur <jkacur@redhat.com>, Daniel Wagner <wagi@monom.org>,
	Tom Zanussi <zanussi@kernel.org>,
	"Srivatsa S. Bhat" <srivatsa@csail.mit.edu>,
	kernel test robot <rong.a.chen@intel.com>,
	John Ogness <john.ogness@linutronix.de>
Subject: [PATCH RT 1/8] printk: console must not schedule for drivers
Date: Fri, 05 Jun 2020 19:41:50 -0400
Message-ID: <20200605234221.847811418@goodmis.org> (raw)
In-Reply-To: <20200605234149.965509211@goodmis.org>

5.4.44-rt27-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: John Ogness <john.ogness@linutronix.de>

Even though the printk kthread is always preemptible, it is still not
allowed to call cond_resched() from within console drivers. The
task may become non-preemptible in the console driver call chain. For
example, vt_console_print() takes a spinlock and then can call into
fbcon_redraw(), which can conditionally invoke cond_resched():

|BUG: sleeping function called from invalid context at kernel/printk/printk.c:2322
|in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 177, name: printk
|CPU: 0 PID: 177 Comm: printk Not tainted 5.6.2-00011-ga536059557f1d9 #1
|Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
|Call Trace:
| dump_stack+0x66/0x8b
| ___might_sleep+0x102/0x120
| console_conditional_schedule+0x24/0x30
| fbcon_redraw+0x96/0x1c0
| fbcon_scroll+0x556/0xd70
| con_scroll+0x147/0x1e0
| lf+0x9e/0xb0
| vt_console_print+0x253/0x3d0
| printk_kthread_func+0x1d5/0x3b0

Disable cond_resched() for the call into the console drivers.

Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/printk/printk.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2affe95866a4..9600373bcf55 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2746,6 +2746,7 @@ static int printk_kthread_func(void *data)
 			    &len, printk_time);
 
 		console_lock();
+		console_may_schedule = 0;
 		call_console_drivers(master_seq, ext_text, ext_len, text, len,
 				     msg->level, msg->facility);
 		if (len > 0 || ext_len > 0)
-- 
2.26.2



  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-05 23:41 [PATCH RT 0/8] Linux 5.4.44-rt27-rc1 Steven Rostedt
2020-06-05 23:41 ` Steven Rostedt [this message]
2020-06-05 23:41 ` [PATCH RT 2/8] fs/dcache: Include swait.h header Steven Rostedt
2020-06-05 23:41 ` [PATCH RT 3/8] Revert "rt: Improve the serial console PASS_LIMIT" Steven Rostedt
2020-06-05 23:41 ` [PATCH RT 4/8] mm: Dont warn about atomic memory allocations during suspend Steven Rostedt
2020-06-05 23:41 ` [PATCH RT 5/8] mm: slub: Always flush the delayed empty slubs in flush_all() Steven Rostedt
2020-06-05 23:41 ` [PATCH RT 7/8] mm/zswap: Use local lock to protect per-CPU data Steven Rostedt
2020-06-05 23:41 ` [PATCH RT 8/8] Linux 5.4.44-rt27-rc1 Steven Rostedt

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