On Mon, 18 Jan 2016 09:58:12 +0900 Byungchul Park <byungchul.p...@lge.com>
wrote:
> It causes an infinite recursive cycle when using CONFIG_DEBUG_SPINLOCK,
> in the spin_dump(). Backtrace prints printk() -> console_trylock() ->
> do_raw_spin_lock() -> spint_bug() -> spin_dump() -> printk()...
> infinitely.
>
> If the spin_bug() is called from a function like printk() which is
> trying to obtain the console lock, we should prevent the debug spinlock
> code from calling printk() again in that context.
>
lol. Excellent.
> --- a/kernel/locking/spinlock_debug.c
> +++ b/kernel/locking/spinlock_debug.c
> @@ -67,11 +67,22 @@ static void spin_dump(raw_spinlock_t *lock, const char
> *msg)
> dump_stack();
> }
>
> +extern int is_console_lock(raw_spinlock_t *lock);
> +
> static void spin_bug(raw_spinlock_t *lock, const char *msg)
> {
> if (!debug_locks_off())
> return;
>
> + /*
> + * If this function is called from a function like printk()
> + * which is trying to obtain the console lock, then we should
> + * not call printk() any more. Or it will cause an infinite
> + * recursive cycle!
> + */
> + if (unlikely(is_console_lock(lock)))
> + return;
> +
> spin_dump(lock, msg);
> }
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 2ce8826..50ea552 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -119,6 +119,11 @@ static int __down_trylock_console_sem(unsigned long ip)
> up(&console_sem);\
> } while (0)
>
> +int is_console_lock(raw_spinlock_t *lock)
> +{
> + return &console_sem.lock == lock;
> +}
> +
> /*
> * This is used for debugging the mess that is the VT code by
> * keeping track if we have the console semaphore held. It's
I can't immediately think of anything better than this. It's a hack, but
it's a small and quite clear hack.
