Re: [PATCH v2] perf/core: Fix double put of the system-wide perf_ctx_data reference

[sashiko-bot@kernel.org]

> The reference on a task's perf_ctx_data that belongs to the system-wide
> events (cd->global) can be put twice. __detach_global_ctx_data() puts it
> when the last system-wide event goes away, and perf_event_exit_task()
> puts it again when the task exits. perf_event_exit_task() runs without
> global_ctx_data_rwsem and never clears cd->global, so nothing stops both
> paths from putting the same reference:
> 
>   CPU0                               CPU1 (task T exiting)
>   __detach_global_ctx_data()
>     cd->global = 0;
>     detach_task_ctx_data(T)
>       refcount_dec_and_test() == true
>                                      perf_event_exit_task(T)
>                                        detach_task_ctx_data(T)
>                                          cd = T->perf_ctx_data;
> [ ... ]
> put it when they are freed.
> 
> Fixes: 506e64e710ff ("perf: attach/detach PMU specific data")
> Assisted-by: Claude:claude-opus-5-5 syzkaller
> Signed-off-by: vineash <vineash30640@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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