On Tue, Jul 12, 2016 at 7:11 PM, Viresh Kumar <[email protected]> wrote: > On 12-07-16, 06:12, Viresh Kumar wrote: > >> Yeah, so I tried debugging this more and I am able to get printing >> done to just before arch_suspend_disable_irqs() in suspend.c and then >> it stops because of the async nature. >> >> I get to this point for both successful suspend/resume (where system >> resumes back successfully) and in the bad case (where the system just >> hangs/crashes). >> >> FWIW, I also tried commenting out following in suspend_enter(): >> >> error = suspend_ops->enter(state); >> >> so that the system doesn't go into suspend at all, and just resume >> back immediately (similar to TEST_CORE) and I saw the hang/crash then >> as well one of the times. > > So I tried it cleanly without any local hacks using: > > echo core > /sys/power/pm_test > > and I still see the problem, so whatever happens, happens before > putting the system into complete suspend. > > FWIW, I also tried this hacky thing: > > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c > index bc71478fac26..045ebc88fe08 100644 > --- a/kernel/power/suspend.c > +++ b/kernel/power/suspend.c > @@ -170,6 +170,7 @@ void __attribute__ ((weak)) arch_suspend_enable_irqs(void) > * > * This function should be called after devices have been suspended. > */ > +extern bool printk_sync_suspended; > static int suspend_enter(suspend_state_t state, bool *wakeup) > { > char suspend_abort[MAX_SUSPEND_ABORT_LEN]; > @@ -218,6 +219,7 @@ static int suspend_enter(suspend_state_t state, bool > *wakeup) > } > > arch_suspend_disable_irqs(); > + printk_sync_suspended = true; > BUG_ON(!irqs_disabled()); > > error = syscore_suspend(); > @@ -237,6 +239,7 @@ static int suspend_enter(suspend_state_t state, bool > *wakeup) > syscore_resume(); > } > > + printk_sync_suspended = false; > arch_suspend_enable_irqs(); > BUG_ON(irqs_disabled()); > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 46bb017ac2c9..187054074b96 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -293,6 +293,7 @@ static u32 log_buf_len = __LOG_BUF_LEN; > > /* Control whether printing to console must be synchronous. */ > static bool __read_mostly printk_sync = false; > +bool printk_sync_suspended = false; > /* Printing kthread for async printk */ > static struct task_struct *printk_kthread; > /* When `true' printing thread has messages to print */ > @@ -300,7 +301,7 @@ static bool printk_kthread_need_flush_console; > > static inline bool can_printk_async(void) > { > - return !printk_sync && printk_kthread; > + return !printk_sync && !printk_sync_suspended && printk_kthread; > } > > /* Return log buffer address */ > > > i.e. I disabled async-printk after interrupts are disabled on the last > running CPU (0) and enabled it again before enabling interrupts back. > > This FIXES the hangs for me :) > > I don't think its a crash but some sort of deadlock in async printk > thread because of the state it was left in before we offlined all > other CPUs and disabled interrupts on the local one.
It looks like a new printk() waits for a previous one to make progress and since progress cannot be made under the suspend conditions, it waits forever.
