Commit-ID: 2a2301058898c4146b87461b3054a1cbeaee9a0e Gitweb: http://git.kernel.org/tip/2a2301058898c4146b87461b3054a1cbeaee9a0e Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Tue, 19 Nov 2013 16:42:47 +0100 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Sat, 30 Nov 2013 15:18:42 +0100
lockdep: Correctly annotate hardirq context in irq_exit() 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. Reported-by: Sebastian Andrzej Siewior <bige...@linutronix.de> Cc: Frederic Weisbecker <fweis...@gmail.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/n/tip-dgwc5cdksbn0jk09vbmcc...@git.kernel.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/softirq.c | 54 +++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 45 insertions(+), 9 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 11025cc..f84aa48 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -211,14 +211,52 @@ 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) { - struct softirq_action *h; - __u32 pending; unsigned long end = jiffies + MAX_SOFTIRQ_TIME; - int cpu; unsigned long old_flags = current->flags; int max_restart = MAX_SOFTIRQ_RESTART; + struct softirq_action *h; + __u32 pending; + int cpu; /* * Mask out PF_MEMALLOC s current task context is borrowed for the @@ -231,7 +269,7 @@ asmlinkage void __do_softirq(void) account_irq_enter_time(current); __local_bh_disable(_RET_IP_, SOFTIRQ_OFFSET); - lockdep_softirq_enter(); + lockdep_softirq_start(); cpu = smp_processor_id(); restart: @@ -278,16 +316,13 @@ restart: wakeup_softirqd(); } - lockdep_softirq_exit(); - + lockdep_softirq_end(); account_irq_exit_time(current); __local_bh_enable(SOFTIRQ_OFFSET); WARN_ON_ONCE(in_interrupt()); tsk_restore_flags(current, old_flags, PF_MEMALLOC); } - - asmlinkage void do_softirq(void) { __u32 pending; @@ -330,6 +365,7 @@ void irq_enter(void) static inline void invoke_softirq(void) { if (!force_irqthreads) { + lockdep_softirq_from_hardirq(); #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK /* * We can safely execute softirq on the current stack if @@ -375,13 +411,13 @@ void irq_exit(void) #endif account_irq_exit_time(current); - trace_hardirq_exit(); preempt_count_sub(HARDIRQ_OFFSET); if (!in_interrupt() && local_softirq_pending()) invoke_softirq(); tick_irq_exit(); rcu_irq_exit(); + trace_hardirq_exit(); /* must be last! */ } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
