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_cursor+0x100/0x190 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@xxxxxxxxx> Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx> --- kernel/printk/printk.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8821a8c2263f..8bc683be0857 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2715,6 +2715,7 @@ 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) -- 2.19.0
