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SubjectRe: [PATCH 1/3] notifier: Fix broken error handling pattern
On Mon, Jun 24, 2019 at 11:18:44AM +0200, Peter Zijlstra wrote:
> The current notifiers have the following error handling pattern all
> over the place:
>
> int nr;
>
> ret = __foo_notifier_call_chain(&chain, val_up, v, -1, &nr);
> if (err & NOTIFIER_STOP_MASK)

s/err/ret/

> __foo_notifier_call_chain(&chain, val_down, v, nr-1, NULL)
>
> And aside from the endless repetition thereof, it is broken. Consider
> blocking notifiers; both calls take and drop the rwsem, this means
> that the notifier list can change in between the two calls, making @nr
> meaningless.
>
> Fix this by replacing all the __foo_notifier_call_chain() functions
> with foo_notifier_call_chain_error() that embeds the above patter, but
> ensures it is inside a single lock region.

The name "notifier_call_chain_error()" seems confusing, it almost sounds
like it's notifying an error code. Then again, I can't really think of
a more reasonably succinct name.

> @@ -25,8 +25,23 @@ static int cpu_pm_notify(enum cpu_pm_eve
> * RCU know this.
> */
> rcu_irq_enter_irqson();
> - ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL,
> - nr_to_call, nr_calls);
> + ret = atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL);
> + rcu_irq_exit_irqson();
> +
> + return notifier_to_errno(ret);
> +}
> +
> +static int cpu_pm_notify_error(enum cpu_pm_event event_up, enum cpu_pm_event event_down)
> +{
> + int ret;
> +
> + /*
> + * __atomic_notifier_call_chain has a RCU read critical section, which

__atomic_notifier_call_chain() no longer exists.

> + * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let

"dysfunctional"

> @@ -156,43 +169,30 @@ int atomic_notifier_chain_unregister(str
> }
> EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister);
>
> -/**
> - * __atomic_notifier_call_chain - Call functions in an atomic notifier chain
> - * @nh: Pointer to head of the atomic notifier chain
> - * @val: Value passed unmodified to notifier function
> - * @v: Pointer passed unmodified to notifier function
> - * @nr_to_call: See the comment for notifier_call_chain.
> - * @nr_calls: See the comment for notifier_call_chain.
> - *
> - * Calls each function in a notifier chain in turn. The functions
> - * run in an atomic context, so they must not block.
> - * This routine uses RCU to synchronize with changes to the chain.
> - *
> - * If the return value of the notifier can be and'ed
> - * with %NOTIFY_STOP_MASK then atomic_notifier_call_chain()
> - * will return immediately, with the return value of
> - * the notifier function which halted execution.
> - * Otherwise the return value is the return value
> - * of the last notifier function called.
> - */

Why remove the useful comment?

Ditto for the blocking, raw, srcu, comments.

--
Josh

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