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

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Message-ID: <aLldvhYAYwHIlvXi@hu-ashayj-hyd.qualcomm.com>
Date: Thu, 4 Sep 2025 15:07:02 +0530
From: Ashay Jaiswal <quic_ashayj@...cinc.com>
To: Waiman Long <llong@...hat.com>
CC: <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>,
        Michal Koutný
	<mkoutny@...e.com>,
        Tejun Heo <tj@...nel.org>,
        "Peter Zijlstra (Intel)"
	<peterz@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] cpuset: prevent freeing unallocated cpumask in hotplug
 handling

On Tue, Sep 02, 2025 at 02:21:25PM -0400, Waiman Long wrote:
> On 9/2/25 1:14 PM, Waiman Long wrote:
> > 
> > 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@...r.kernel.org
> > > Signed-off-by: Ashay Jaiswal <quic_ashayj@...cinc.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().
> 
> As this email was bounced back from your email account because it is full, I
> decide to send out another patch on your behalf. Note that this affects only
> the linux-next tree as the commit to be fixed isn't merged into the mainline
> yet. There is no need for stable branch backport.
>

Thank you for your help, and I apologize for the email bouncing back.

> Cheers,
> Longman
>