Re: [PATCH] cpuset: prevent freeing unallocated cpumask in hotplug handling

[Waiman Long <llong@redhat.com>]

On 9/2/25 12:26 AM, Ashay Jaiswal wrote:
> In cpuset hotplug handling, temporary cpumasks are allocated only when
> running under cgroup v2. The current code unconditionally frees these
> masks, which can lead to a crash on cgroup v1 case.
>
> Free the temporary cpumasks only when they were actually allocated.
>
> Fixes: 4b842da276a8 ("cpuset: Make CPU hotplug work with partition")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ashay Jaiswal <quic_ashayj@quicinc.com>
> ---
>   kernel/cgroup/cpuset.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index a78ccd11ce9b43c2e8b0e2c454a8ee845ebdc808..a4f908024f3c0a22628a32f8a5b0ae96c7dccbb9 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -4019,7 +4019,8 @@ static void cpuset_handle_hotplug(void)
>   	if (force_sd_rebuild)
>   		rebuild_sched_domains_cpuslocked();
>   
> -	free_tmpmasks(ptmp);
> +	if (on_dfl && ptmp)
> +		free_tmpmasks(ptmp);
>   }
>   
>   void cpuset_update_active_cpus(void)
The patch that introduces the bug is actually commit 5806b3d05165 
("cpuset: decouple tmpmasks and cpumasks freeing in cgroup") which 
removes the NULL check. The on_dfl check is not necessary and I would 
suggest adding the NULL check in free_tmpmasks().

Cheers,
Longman