On Tuesday, August 15, 2017 4:56:18 AM CEST Sergey Senozhatsky wrote: > It's not always possible/safe to wake_up() printk kernel > thread. For example, late suspend/early resume may printk() > while timekeeping is not initialized yet, so calling into the > scheduler may result in recursive warnings. > > Another thing to notice is the fact that PM at some point > freezes user space and kernel threads: freeze_processes() > and freeze_kernel_threads(), correspondingly. Thus we need > printk() to operate in emergency mode there and attempt to > immediately flush pending kernel message to the console. > > This patch registers PM notifier, so PM can switch printk > to emergency mode from PM_FOO_PREPARE notifiers and return
Isn't that too early? That's before user space is frozen even. > back to printk threaded mode from PM_POST_FOO notifiers. And isn't that too late? > Signed-off-by: Sergey Senozhatsky <[email protected]> > Suggested-by: Andreas Mohr <[email protected]> > --- > kernel/printk/printk.c | 35 +++++++++++++++++++++++++++++++++++ > 1 file changed, 35 insertions(+) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 05165f008bc8..d3f149fad85c 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -49,6 +49,7 @@ > #include <linux/sched/debug.h> > #include <linux/sched/task_stack.h> > #include <linux/kthread.h> > +#include <linux/suspend.h> > > #include <linux/uaccess.h> > #include <asm/sections.h> > @@ -2913,6 +2914,33 @@ static DEFINE_PER_CPU(struct irq_work, > wake_up_klogd_work) = { > .flags = IRQ_WORK_LAZY, > }; > > +static int printk_pm_notify(struct notifier_block *notify_block, > + unsigned long mode, void *unused) > +{ > + switch (mode) { > + case PM_HIBERNATION_PREPARE: > + case PM_SUSPEND_PREPARE: > + case PM_RESTORE_PREPARE: > + printk_emergency_begin_sync(); I'm not sure what would be wrong with calling this directly from dpm_suspend_noirq(). > + break; > + > + case PM_POST_SUSPEND: > + case PM_POST_HIBERNATION: > + case PM_POST_RESTORE: > + printk_emergency_end_sync(); And this could be called from dpm_resume_noirq(). In which case you wouldn't really need the stuff below. Thanks, Rafael
