On Sun, 11 Nov 2018 11:32:14 -0800
"Paul E. McKenney" <paul...@linux.ibm.com> wrote:
> The sync.c file has a number of calls to BUG_ON(), which panics the
> kernel, which is not a good strategy for devices (like embedded) that
> don't have a way to capture console output. This commit therefore
> changes these BUG_ON() calls to WARN_ON_ONCE(), but does so quite naively.
>
> Reported-by: Linus Torvalds <torva...@linux-foundation.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.ibm.com>
> Acked-by: Oleg Nesterov <o...@redhat.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> ---
> kernel/rcu/sync.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
> index 3f943efcf61c..a6ba446a9693 100644
> --- a/kernel/rcu/sync.c
> +++ b/kernel/rcu/sync.c
> @@ -125,8 +125,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
> rsp->gp_state = GP_PENDING;
> spin_unlock_irq(&rsp->rss_lock);
>
> - BUG_ON(need_wait && need_sync);
> -
> + WARN_ON_ONCE(need_wait && need_sync);
> if (need_sync) {
> gp_ops[rsp->gp_type].sync();
> rsp->gp_state = GP_PASSED;
> @@ -139,7 +138,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
> * Nobody has yet been allowed the 'fast' path and thus we can
> * avoid doing any sync(). The callback will get 'dropped'.
> */
> - BUG_ON(rsp->gp_state != GP_PASSED);
> + WARN_ON_ONCE(rsp->gp_state != GP_PASSED);
> }
> }
>
> @@ -166,8 +165,8 @@ static void rcu_sync_func(struct rcu_head *rhp)
> struct rcu_sync *rsp = container_of(rhp, struct rcu_sync, cb_head);
> unsigned long flags;
>
> - BUG_ON(rsp->gp_state != GP_PASSED);
> - BUG_ON(rsp->cb_state == CB_IDLE);
> + WARN_ON_ONCE(rsp->gp_state != GP_PASSED);
> + WARN_ON_ONCE(rsp->cb_state == CB_IDLE);
>
> spin_lock_irqsave(&rsp->rss_lock, flags);
> if (rsp->gp_count) {
> @@ -225,7 +224,7 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
> {
> int cb_state;
>
> - BUG_ON(rsp->gp_count);
> + WARN_ON_ONCE(rsp->gp_count);
>
> spin_lock_irq(&rsp->rss_lock);
> if (rsp->cb_state == CB_REPLAY)
> @@ -235,6 +234,6 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
>
> if (cb_state != CB_IDLE) {
> gp_ops[rsp->gp_type].wait();
> - BUG_ON(rsp->cb_state != CB_IDLE);
> + WARN_ON_ONCE(rsp->cb_state != CB_IDLE);
> }
> }
I take it that if any of these WARN_ON_ONCE() triggers, they wont cause
immediate catastrophe, and/or there's no gentle way out like you have
with the other patches exiting the function when one is hit.
-- Steve
