On 07/27/2016 12:38 PM, Ingo Molnar wrote:
* Vegard Nossum <[email protected]> wrote:
I'm assuming you want to declare and initialise preempt_disable_ip at
once here, but it generates slightly worse code since it dereferences
current->preempt_disable_ip in the "fast path" (i.e. a sleeping
function is NOT called from an invalid context).
Could you please add a likely() branch to see whether GCC will delay the
initialization?
The 4 #ifdefs were really ugly, so yes, it would be nice to at least reduce them
to 2.
How about this?
Vegard
>From 9d0e4bb63f0fada627a4f99432db8d39add487b4 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <[email protected]>
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:[<ffffffff8119db33>] 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:[<ffffffff811aaa37>] 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:[<ffffffff819bcd46>] rhashtable_walk_start+0x46/0x150
(Bug report: http://marc.info/?l=linux-netdev&m=146925979821849&w=2)
Cc: Peter Zijlstra <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Rusty Russel <[email protected]>
Signed-off-by: Vegard Nossum <[email protected]>
---
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 253538f2..cdbcc2e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3142,6 +3142,15 @@ 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 7171cf9..afd2403 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3144,6 +3144,9 @@ 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;
@@ -3154,13 +3157,12 @@ 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
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
@@ -7541,6 +7543,7 @@ 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() &&
@@ -7551,6 +7554,9 @@ 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);
@@ -7565,13 +7571,12 @@ 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();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
--
1.9.1
