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    Subject[PATCH 5.15 656/779] sched, cpuset: Fix dl_cpu_busy() panic due to empty cs->cpus_allowed
    Date
    From: Waiman Long <longman@redhat.com>

    [ Upstream commit b6e8d40d43ae4dec00c8fea2593eeea3114b8f44 ]

    With cgroup v2, the cpuset's cpus_allowed mask can be empty indicating
    that the cpuset will just use the effective CPUs of its parent. So
    cpuset_can_attach() can call task_can_attach() with an empty mask.
    This can lead to cpumask_any_and() returns nr_cpu_ids causing the call
    to dl_bw_of() to crash due to percpu value access of an out of bound
    CPU value. For example:

    [80468.182258] BUG: unable to handle page fault for address: ffffffff8b6648b0
    :
    [80468.191019] RIP: 0010:dl_cpu_busy+0x30/0x2b0
    :
    [80468.207946] Call Trace:
    [80468.208947] cpuset_can_attach+0xa0/0x140
    [80468.209953] cgroup_migrate_execute+0x8c/0x490
    [80468.210931] cgroup_update_dfl_csses+0x254/0x270
    [80468.211898] cgroup_subtree_control_write+0x322/0x400
    [80468.212854] kernfs_fop_write_iter+0x11c/0x1b0
    [80468.213777] new_sync_write+0x11f/0x1b0
    [80468.214689] vfs_write+0x1eb/0x280
    [80468.215592] ksys_write+0x5f/0xe0
    [80468.216463] do_syscall_64+0x5c/0x80
    [80468.224287] entry_SYSCALL_64_after_hwframe+0x44/0xae

    Fix that by using effective_cpus instead. For cgroup v1, effective_cpus
    is the same as cpus_allowed. For v2, effective_cpus is the real cpumask
    to be used by tasks within the cpuset anyway.

    Also update task_can_attach()'s 2nd argument name to cs_effective_cpus to
    reflect the change. In addition, a check is added to task_can_attach()
    to guard against the possibility that cpumask_any_and() may return a
    value >= nr_cpu_ids.

    Fixes: 7f51412a415d ("sched/deadline: Fix bandwidth check/update when migrating tasks between exclusive cpusets")
    Signed-off-by: Waiman Long <longman@redhat.com>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Acked-by: Juri Lelli <juri.lelli@redhat.com>
    Link: https://lore.kernel.org/r/20220803015451.2219567-1-longman@redhat.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/linux/sched.h | 2 +-
    kernel/cgroup/cpuset.c | 2 +-
    kernel/sched/core.c | 8 +++++---
    3 files changed, 7 insertions(+), 5 deletions(-)

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index ad7ff332a0ac..dcba347cbffa 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1797,7 +1797,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
    }

    extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
    -extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed);
    +extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
    #ifdef CONFIG_SMP
    extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
    extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
    diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
    index 31f94c6ea0a5..9c5b659db63f 100644
    --- a/kernel/cgroup/cpuset.c
    +++ b/kernel/cgroup/cpuset.c
    @@ -2199,7 +2199,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
    goto out_unlock;

    cgroup_taskset_for_each(task, css, tset) {
    - ret = task_can_attach(task, cs->cpus_allowed);
    + ret = task_can_attach(task, cs->effective_cpus);
    if (ret)
    goto out_unlock;
    ret = security_task_setscheduler(task);
    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 154506e4d1f5..5c7937b504d2 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -8741,7 +8741,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
    }

    int task_can_attach(struct task_struct *p,
    - const struct cpumask *cs_cpus_allowed)
    + const struct cpumask *cs_effective_cpus)
    {
    int ret = 0;

    @@ -8760,9 +8760,11 @@ int task_can_attach(struct task_struct *p,
    }

    if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
    - cs_cpus_allowed)) {
    - int cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed);
    + cs_effective_cpus)) {
    + int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);

    + if (unlikely(cpu >= nr_cpu_ids))
    + return -EINVAL;
    ret = dl_cpu_busy(cpu, p);
    }

    --
    2.35.1


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