From d1c6d149cf04d6c7c3c3ebf4b66c82500cbcf6e1 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Sat, 23 Jul 2016 09:46:39 +0200 Subject: [PATCH] sched/debug: Make the "Preemption disabled at ..." message more useful This message is currently really useless since it always prints a value that comes from the printk() we just did, e.g.: BUG: sleeping function called from invalid context at mm/slab.h:388 in_atomic(): 0, irqs_disabled(): 0, pid: 31996, name: trinity-c1 Preemption disabled at:[] down_trylock+0x13/0x80 BUG: sleeping function called from invalid context at include/linux/freezer.h:56 in_atomic(): 0, irqs_disabled(): 0, pid: 31996, name: trinity-c1 Preemption disabled at:[] console_unlock+0x2f7/0x930 Here, both down_trylock() and console_unlock() is somewhere in the printk() path. We should save the value before calling printk() and use the saved value instead. That immediately reveals the offending callsite: BUG: sleeping function called from invalid context at mm/slab.h:388 in_atomic(): 0, irqs_disabled(): 0, pid: 14971, name: trinity-c2 Preemption disabled at:[] rhashtable_walk_start+0x46/0x150 Bug report: http://marc.info/?l=linux-netdev&m=146925979821849&w=2 Signed-off-by: Vegard Nossum Cc: Andrew Morton Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Rusty Russel Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- include/linux/sched.h | 9 +++++++++ kernel/sched/core.c | 21 +++++++++++++-------- 2 files changed, 22 insertions(+), 8 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index f3db596efd2c..7f64e89a5873 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -3236,6 +3236,15 @@ static inline void cond_resched_rcu(void) #endif } +static inline unsigned long get_preempt_disable_ip(struct task_struct *p) +{ +#ifdef CONFIG_DEBUG_PREEMPT + return p->preempt_disable_ip; +#else + return 0; +#endif +} + /* * Does a critical section need to be broken due to another * task waiting?: (technically does not depend on CONFIG_PREEMPT, diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 10f2595c408a..a65681605aef 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3171,6 +3171,9 @@ static inline void preempt_latency_stop(int val) { } */ static noinline void __schedule_bug(struct task_struct *prev) { + /* Save this before calling printk(), since that will clobber it */ + unsigned long preempt_disable_ip = get_preempt_disable_ip(current); + if (oops_in_progress) return; @@ -3181,13 +3184,12 @@ static noinline void __schedule_bug(struct task_struct *prev) print_modules(); if (irqs_disabled()) print_irqtrace_events(prev); -#ifdef CONFIG_DEBUG_PREEMPT - if (in_atomic_preempt_off()) { + if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) + && in_atomic_preempt_off()) { pr_err("Preemption disabled at:"); - print_ip_sym(current->preempt_disable_ip); + print_ip_sym(preempt_disable_ip); pr_cont("\n"); } -#endif if (panic_on_warn) panic("scheduling while atomic\n"); @@ -7571,6 +7573,7 @@ EXPORT_SYMBOL(__might_sleep); void ___might_sleep(const char *file, int line, int preempt_offset) { static unsigned long prev_jiffy; /* ratelimiting */ + unsigned long preempt_disable_ip; rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */ if ((preempt_count_equals(preempt_offset) && !irqs_disabled() && @@ -7581,6 +7584,9 @@ void ___might_sleep(const char *file, int line, int preempt_offset) return; prev_jiffy = jiffies; + /* Save this before calling printk(), since that will clobber it */ + preempt_disable_ip = get_preempt_disable_ip(current); + printk(KERN_ERR "BUG: sleeping function called from invalid context at %s:%d\n", file, line); @@ -7595,13 +7601,12 @@ void ___might_sleep(const char *file, int line, int preempt_offset) debug_show_held_locks(current); if (irqs_disabled()) print_irqtrace_events(current); -#ifdef CONFIG_DEBUG_PREEMPT - if (!preempt_count_equals(preempt_offset)) { + if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) + && !preempt_count_equals(preempt_offset)) { pr_err("Preemption disabled at:"); - print_ip_sym(current->preempt_disable_ip); + print_ip_sym(preempt_disable_ip); pr_cont("\n"); } -#endif dump_stack(); } EXPORT_SYMBOL(___might_sleep); -- 2.39.5