On Fri, 15 Feb 2013 17:57:10 +0100 Jan Kara <[email protected]> wrote: > A CPU can be caught in console_unlock() for a long time (tens of seconds are > reported by our customers) when other CPUs are using printk heavily and serial > console makes printing slow. Despite serial console drivers are calling > touch_nmi_watchdog() this triggers softlockup warnings because > interrupts are disabled for the whole time console_unlock() runs (e.g. > vprintk() calls console_unlock() with interrupts disabled). Thus IPIs > cannot be processed and other CPUs get stuck spinning in calls like > smp_call_function_many(). Also RCU eventually starts reporting lockups. > > In my artifical testing I also managed to trigger a situation when disk > disappeared from the system apparently because commands to / from it > could not be delivered for long enough. This is why just silencing > watchdogs isn't a reliable solution to the problem and we simply have to > avoid spending too long in console_unlock(). > > We fix the issue by limiting the time we spend in console_unlock() to > watchdog_thresh() / 4 (unless we are in an early boot stage or oops is > happening). The rest of the buffer will be printed either by further > callers to printk() or during next timer tick. >
It still gives me tummy ache :( The patch adds additional tests of oops_in_progress. Some description of your thinking on that matter would be appropriate? > --- a/kernel/printk.c > +++ b/kernel/printk.c > @@ -1990,17 +1990,31 @@ int is_console_locked(void) > #define PRINTK_PENDING_OUTPUT 2 > > static unsigned long printk_pending; > +static int last_printing_cpu = -1; > + > +static bool __console_unlock(void); > > void printk_tick(void) printk_tick() no longer exists in linux-next. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
