Messages in this thread Patch in this message | | | Subject | Re: [PATCH] printk: robustify printk | From | Peter Zijlstra <> | Date | Fri, 08 Aug 2008 21:47:09 +0200 |
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On Fri, 2008-08-08 at 21:21 +0200, Peter Zijlstra wrote:
> The initial printk_tick() based implementation didn't suffer this > problem, should we revert to that scheme?
Just in case people care..
--- Subject: printk: robustify printk
Avoid deadlocks against rq->lock and xtime_lock by deferring the klogd wakeup by polling from the timer tick.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- include/linux/kernel.h | 4 ++++ kernel/printk.c | 19 +++++++++++++++++-- kernel/time/tick-sched.c | 2 +- kernel/timer.c | 1 + 4 files changed, 23 insertions(+), 3 deletions(-)
Index: linux-2.6/include/linux/kernel.h =================================================================== --- linux-2.6.orig/include/linux/kernel.h +++ linux-2.6/include/linux/kernel.h @@ -200,6 +200,8 @@ extern struct ratelimit_state printk_rat extern int printk_ratelimit(void); extern bool printk_timed_ratelimit(unsigned long *caller_jiffies, unsigned int interval_msec); +extern void printk_tick(void); +extern int printk_needs_cpu(int); #else static inline int vprintk(const char *s, va_list args) __attribute__ ((format (printf, 1, 0))); @@ -211,6 +213,8 @@ static inline int printk_ratelimit(void) static inline bool printk_timed_ratelimit(unsigned long *caller_jiffies, \ unsigned int interval_msec) \ { return false; } +static inline void printk_tick(void) { } +static inline int printk_needs_cpu(int) { return 0; } #endif extern void asmlinkage __attribute__((format(printf, 1, 2))) Index: linux-2.6/kernel/printk.c =================================================================== --- linux-2.6.orig/kernel/printk.c +++ linux-2.6/kernel/printk.c @@ -982,10 +982,25 @@ int is_console_locked(void) return console_locked; } -void wake_up_klogd(void) +static DEFINE_PER_CPU(int, printk_pending); + +void printk_tick(void) { - if (!oops_in_progress && waitqueue_active(&log_wait)) + if (__get_cpu_var(printk_pending)) { + __get_cpu_var(printk_pending) = 0; wake_up_interruptible(&log_wait); + } +} + +int printk_needs_cpu(int cpu) +{ + return per_cpu(printk_pending, cpu); +} + +void wake_up_klogd(void) +{ + if (waitqueue_active(&log_wait)) + __get_cpu_var(printk_pending) = 1; } /** Index: linux-2.6/kernel/time/tick-sched.c =================================================================== --- linux-2.6.orig/kernel/time/tick-sched.c +++ linux-2.6/kernel/time/tick-sched.c @@ -255,7 +255,7 @@ void tick_nohz_stop_sched_tick(int inidl next_jiffies = get_next_timer_interrupt(last_jiffies); delta_jiffies = next_jiffies - last_jiffies; - if (rcu_needs_cpu(cpu)) + if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu)) delta_jiffies = 1; /* * Do not stop the tick, if we are only one off Index: linux-2.6/kernel/timer.c =================================================================== --- linux-2.6.orig/kernel/timer.c +++ linux-2.6/kernel/timer.c @@ -978,6 +978,7 @@ void update_process_times(int user_tick) run_local_timers(); if (rcu_pending(cpu)) rcu_check_callbacks(cpu, user_tick); + printk_tick(); scheduler_tick(); run_posix_cpu_timers(p); }
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