Re: [PATCH] x86/aperfmperf: Fix deadlock on cpu_hotplug_lock

[Thomas Gleixner]

On Mon, Jul 29 2024 at 11:55, Jonathan Cameron wrote:
> The broken patch results in a call to init_freq_invariance_cppc() in a CPU
> hotplug handler in both the path for initially present CPUs and those
> hotplugged later.  That function includes a one time call to
> amd_set_max_freq_ratio() which in turn calls freq_invariance_enable() that
> has a static_branch_enable() which takes the cpu_hotlug_lock which is
> already held.
>
> Avoid the deadlock by using static_branch_enable_cpuslocked() as the lock
> will always be already held.  The equivalent path on Intel does not
> already hold this lock, so take it around the call to
> freq_invariance_enable(), which results in it being held over the call to
> register_syscall_ops, which looks to be safe to do.
>
> Fixes: c1385c1f0ba3 ("ACPI: processor: Simplify initial onlining to use same path for cold and hotplug")
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> Closes: https://lore.kernel.org/all/CABXGCsPvqBfL5hQDOARwfqasLRJ_eNPBbCngZ257HOe=xbWDkA@xxxxxxxxxxxxxx/
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>