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sched, cpuset: Fix dl_cpu_busy() panic due to empty cs->cpus_allowed

Waiman Long requested to merge llong1/centos-stream-9:bz2104946_sched into main

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2104946
MR: !1222 (merged)
Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=sched/urgent&id=b6e8d40d43ae4dec00c8fea2593eeea3114b8f44

commit b6e8d40d43ae4dec00c8fea2593eeea3114b8f44
Author: Waiman Long longman@redhat.com
Date: Tue, 2 Aug 2022 21:54:51 -0400

sched, cpuset: Fix dl_cpu_busy() panic due to empty cs->cpus_allowed

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: Waiman Long longman@redhat.com

Edited by Waiman Long

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