* Vegard Nossum <vegard.nos...@oracle.com> wrote:
> 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 <pet...@infradead.org>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Rusty Russel <ru...@rustcorp.com.au>
> Signed-off-by: Vegard Nossum <vegard.nos...@oracle.com>
> ---
> kernel/sched/core.c | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7171cf9..87689a6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3144,9 +3144,18 @@ static inline void preempt_latency_stop(int val) { }
> */
> static noinline void __schedule_bug(struct task_struct *prev)
> {
> +#ifdef CONFIG_DEBUG_PREEMPT
> + unsigned long preempt_disable_ip;
> +#endif
> +
> if (oops_in_progress)
> return;
>
> +#ifdef CONFIG_DEBUG_PREEMPT
> + /* Save this before calling printk(), since that will clobber it */
> + preempt_disable_ip = current->preempt_disable_ip;
> +#endif
These two blocks could be merged trivially, avoiding an #ifdef pair ...
> +
> printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
> prev->comm, prev->pid, preempt_count());
>
> @@ -3157,7 +3166,7 @@ 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 +7550,9 @@ 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
> + unsigned long preempt_disable_ip;
> +#endif
>
> rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
> if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
> @@ -7551,6 +7563,11 @@ void ___might_sleep(const char *file, int line, int
> preempt_offset)
> return;
> prev_jiffy = jiffies;
>
> +#ifdef CONFIG_DEBUG_PREEMPT
> + /* Save this before calling printk(), since that will clobber it */
> + preempt_disable_ip = current->preempt_disable_ip;
> +#endif
> +
> printk(KERN_ERR
> "BUG: sleeping function called from invalid context at %s:%d\n",
> file, line);
> @@ -7568,7 +7585,7 @@ 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");
Ditto.
Thanks,
Ingo
