3.10.22-rt20-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> There was a reported deadlock on -rt which lockdep didn't report. It turns out that in irq_exit() we tell lockdep that the hardirq context ends and then do all kinds of locking afterwards. To fix it, move trace_hardirq_exit() to the very end of irq_exit(), this ensures all locking in tick_irq_exit() and rcu_irq_exit() are properly recorded as happening from hardirq context. This however leads to the 'fun' little problem of running softirqs while in hardirq context. To cure this make the softirq code a little more complex (in the CONFIG_TRACE_IRQFLAGS case). Due to stack swizzling arch dependent trickery we cannot pass an argument to __do_softirq() to tell it if it was done from hardirq context or not; so use a side-band argument. When we do __do_softirq() from hardirq context, 'atomically' flip to softirq context and back, so that no locking goes without being in either hard- or soft-irq context. I didn't find any new problems in mainline using this patch, but it did show the -rt problem. Cc: stable-rt@xxxxxxxxxxxxxxx Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Link: http://lkml.kernel.org/n/tip-dgwc5cdksbn0jk09vbmcc9sa@xxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- kernel/softirq.c | 46 ++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 42 insertions(+), 4 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 4cacbcd..541adf3 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -355,6 +355,44 @@ EXPORT_SYMBOL(local_bh_enable_ip); #define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) #define MAX_SOFTIRQ_RESTART 10 +#ifdef CONFIG_TRACE_IRQFLAGS +/* + * Convoluted means of passing __do_softirq() a message through the various + * architecture execute_on_stack() bits. + * + * When we run softirqs from irq_exit() and thus on the hardirq stack we need + * to keep the lockdep irq context tracking as tight as possible in order to + * not miss-qualify lock contexts and miss possible deadlocks. + */ +static DEFINE_PER_CPU(int, softirq_from_hardirq); + +static inline void lockdep_softirq_from_hardirq(void) +{ + this_cpu_write(softirq_from_hardirq, 1); +} + +static inline void lockdep_softirq_start(void) +{ + if (this_cpu_read(softirq_from_hardirq)) + trace_hardirq_exit(); + lockdep_softirq_enter(); +} + +static inline void lockdep_softirq_end(void) +{ + lockdep_softirq_exit(); + if (this_cpu_read(softirq_from_hardirq)) { + this_cpu_write(softirq_from_hardirq, 0); + trace_hardirq_enter(); + } +} + +#else +static inline void lockdep_softirq_from_hardirq(void) { } +static inline void lockdep_softirq_start(void) { } +static inline void lockdep_softirq_end(void) { } +#endif + asmlinkage void __do_softirq(void) { __u32 pending; @@ -375,7 +413,7 @@ asmlinkage void __do_softirq(void) __local_bh_disable((unsigned long)__builtin_return_address(0), SOFTIRQ_OFFSET); - lockdep_softirq_enter(); + lockdep_softirq_start(); cpu = smp_processor_id(); restart: @@ -393,8 +431,7 @@ restart: wakeup_softirqd(); } - lockdep_softirq_exit(); - + lockdep_softirq_end(); account_irq_exit_time(current); __local_bh_enable(SOFTIRQ_OFFSET); tsk_restore_flags(current, old_flags, PF_MEMALLOC); @@ -700,6 +737,7 @@ static inline void invoke_softirq(void) { #ifndef CONFIG_PREEMPT_RT_FULL if (!force_irqthreads) { + lockdep_softirq_from_hardirq(); /* * We can safely execute softirq on the current stack if * it is the irq stack, because it should be near empty @@ -749,13 +787,13 @@ void irq_exit(void) #endif account_irq_exit_time(current); - trace_hardirq_exit(); sub_preempt_count(HARDIRQ_OFFSET); if (!in_interrupt() && local_softirq_pending()) invoke_softirq(); tick_irq_exit(); rcu_irq_exit(); + trace_hardirq_exit(); /* must be last! */ } void raise_softirq(unsigned int nr) -- 1.8.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
