From 8d91f8b15361dfb438ab6eb3b319e2ded43458ff Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 15 Jan 2016 16:58:24 -0800 Subject: printk: do cond_resched() between lines while outputting to consoles @console_may_schedule tracks whether console_sem was acquired through lock or trylock. If the former, we're inside a sleepable context and console_conditional_schedule() performs cond_resched(). This allows console drivers which use console_lock for synchronization to yield while performing time-consuming operations such as scrolling. However, the actual console outputting is performed while holding irq-safe logbuf_lock, so console_unlock() clears @console_may_schedule before starting outputting lines. Also, only a few drivers call console_conditional_schedule() to begin with. This means that when a lot of lines need to be output by console_unlock(), for example on a console registration, the task doing console_unlock() may not yield for a long time on a non-preemptible kernel. If this happens with a slow console devices, for example a serial console, the outputting task may occupy the cpu for a very long time. Long enough to trigger softlockup and/or RCU stall warnings, which in turn pile more messages, sometimes enough to trigger the next cycle of warnings incapacitating the system. Fix it by making console_unlock() insert cond_resched() between lines if @console_may_schedule. Signed-off-by: Tejun Heo Reported-by: Calvin Owens Acked-by: Jan Kara Cc: Dave Jones Cc: Kyle McMartin Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/panic.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel/panic.c') diff --git a/kernel/panic.c b/kernel/panic.c index b333380c6bb2..d96469de72dc 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -180,8 +180,7 @@ void panic(const char *fmt, ...) * panic() is not being callled from OOPS. */ debug_locks_off(); - console_trylock(); - console_unlock(); + console_flush_on_panic(); if (!panic_blink) panic_blink = no_blink; -- cgit