Re: #syz test: perf/core: Prevent WARN_ON(!ctx) in __free_event for partial init failure

[syzbot <syzbot+ff3aa851d46ab82953a3@syzkaller.appspotmail.com>]

> Move the get_ctx(child_ctx) call and the child_event->ctx assignment
> to occur immediately after the child event is allocated via
> perf_event_alloc(). This ensures that child_event->ctx is always
> non-NULL before any subsequent error path within inherit_event calls
> free_event(), satisfying the assumptions of the cleanup code.
>
> Reported-by: syzbot+ff3aa851d46ab82953a3@syzkaller.appspotmail.com
> Signed-off-by: Gabriel Shahrouzi <gshahrouzi@gmail.com>
> ---
>  kernel/events/core.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 0bb21659e252..153ba622cfa0 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -14016,6 +14016,9 @@ inherit_event(struct perf_event *parent_event,
>  	if (IS_ERR(child_event))
>  		return child_event;
>  
> +	get_ctx(child_ctx);
> +	child_event->ctx = child_ctx;
> +
>  	pmu_ctx = find_get_pmu_context(child_event->pmu, child_ctx, child_event);
>  	if (IS_ERR(pmu_ctx)) {
>  		free_event(child_event);
> @@ -14037,8 +14040,6 @@ inherit_event(struct perf_event *parent_event,
>  		return NULL;
>  	}
>  
> -	get_ctx(child_ctx);
> -
>  	/*
>  	 * Make the child state follow the state of the parent event,
>  	 * not its attr.disabled bit.  We hold the parent's mutex,
> @@ -14059,7 +14060,6 @@ inherit_event(struct perf_event *parent_event,
>  		local64_set(&hwc->period_left, sample_period);
>  	}
>  
> -	child_event->ctx = child_ctx;
>  	child_event->overflow_handler = parent_event->overflow_handler;
>  	child_event->overflow_handler_context
>  		= parent_event->overflow_handler_context;
> -- 
> 2.43.0
>

want either no args or 2 args (repo, branch), got 9