From 332d49d4da90f00304de73c7412311576e2e7f78 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Sat, 23 Jul 2016 09:46:39 +0200 Subject: [PATCH] sched/core: make "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) Cc: Peter Zijlstra Cc: Paul E. McKenney Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Rusty Russel Signed-off-by: Vegard Nossum --- kernel/sched/core.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7171cf9..e06354e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3144,6 +3144,11 @@ static inline void preempt_latency_stop(int val) { } */ static noinline void __schedule_bug(struct task_struct *prev) { +#ifdef CONFIG_DEBUG_PREEMPT + /* Save this before calling printk(), since that will clobber it */ + unsigned long preempt_disable_ip = current->preempt_disable_ip; +#endif + if (oops_in_progress) return; @@ -3157,7 +3162,7 @@ static noinline void __schedule_bug(struct task_struct *prev) #ifdef CONFIG_DEBUG_PREEMPT if (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 @@ -7541,6 +7546,10 @@ EXPORT_SYMBOL(__might_sleep); void ___might_sleep(const char *file, int line, int preempt_offset) { static unsigned long prev_jiffy; /* ratelimiting */ +#ifdef CONFIG_DEBUG_PREEMPT + /* Save this before calling printk(), since that will clobber it */ + unsigned long preempt_disable_ip = current->preempt_disable_ip; +#endif rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */ if ((preempt_count_equals(preempt_offset) && !irqs_disabled() && @@ -7568,7 +7577,7 @@ void ___might_sleep(const char *file, int line, int preempt_offset) #ifdef CONFIG_DEBUG_PREEMPT if (!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 -- 1.9.1