Re: [PATCH] lib/spinlock_debug.c: prevent deadlock in spin_dump() by console_sem
From: Ingo Molnar
Date: Fri Jan 15 2016 - 04:31:03 EST
* Byungchul Park <byungchul.park@xxxxxxx> wrote:
> Deadlock occured when using CONFIG_DEBUG_SPINLOCK, in spin_dump().
> Backtrace prints printk() -> console_trylock() -> do_raw_spin_lock() ->
> spin_dump() -> printk()... infinitely.
> If spin_bug() is called from a function like printk() which is using
> console lock, we should prevent the debug spinlock code from calling
> printk() any more in the context.
> Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
> kernel/locking/spinlock_debug.c | 10 ++++++++++
> kernel/printk/printk.c | 5 +++++
> 2 files changed, 15 insertions(+)
> diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c
> index 0374a59..b339c5e 100644
> --- a/kernel/locking/spinlock_debug.c
> +++ b/kernel/locking/spinlock_debug.c
> @@ -67,11 +67,21 @@ static void spin_dump(raw_spinlock_t *lock, const char *msg)
> +extern int is_console_lock(raw_spinlock_t *lock);
> static void spin_bug(raw_spinlock_t *lock, const char *msg)
> if (!debug_locks_off())
> + /*
> + * If this function is called from a function like printk()
> + * which is trying console lock, we cannot call printk() any
> + * more. Or it's obviously deadlock!
Small spelling nit, the last sentence is not correct, pick one of these variants:
'It's an obvious deadlock.'
'It's obviously a deadlock.'