Syzkaller reported a memory leak as follows:

BUG: memory leak
unreferenced object 0xff110001198ef748 (size 192):
  comm "syz-executor.3", pid 17672, jiffies 4298118891 (age 9.906s)
  hex dump (first 32 bytes):
    00 00 00 00 4a 19 00 00 80 ad e3 e4 fe ff c0 00  ....J...........
    00 b2 d3 0c 01 00 11 ff 28 f5 8e 19 01 00 11 ff  ........(.......
  backtrace:
    [<ffffffffadd28087>] __cpu_map_entry_alloc+0xf7/0xb00
    [<ffffffffadd28d8e>] cpu_map_update_elem+0x2fe/0x3d0
    [<ffffffffadc6d0fd>] bpf_map_update_value.isra.0+0x2bd/0x520
    [<ffffffffadc7349b>] map_update_elem+0x4cb/0x720
    [<ffffffffadc7d983>] __se_sys_bpf+0x8c3/0xb90
    [<ffffffffb029cc80>] do_syscall_64+0x30/0x40
    [<ffffffffb0400099>] entry_SYSCALL_64_after_hwframe+0x61/0xc6

BUG: memory leak
unreferenced object 0xff110001198ef528 (size 192):
  comm "syz-executor.3", pid 17672, jiffies 4298118891 (age 9.906s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffffadd281f0>] __cpu_map_entry_alloc+0x260/0xb00
    [<ffffffffadd28d8e>] cpu_map_update_elem+0x2fe/0x3d0
    [<ffffffffadc6d0fd>] bpf_map_update_value.isra.0+0x2bd/0x520
    [<ffffffffadc7349b>] map_update_elem+0x4cb/0x720
    [<ffffffffadc7d983>] __se_sys_bpf+0x8c3/0xb90
    [<ffffffffb029cc80>] do_syscall_64+0x30/0x40
    [<ffffffffb0400099>] entry_SYSCALL_64_after_hwframe+0x61/0xc6

BUG: memory leak
unreferenced object 0xff1100010fd93d68 (size 8):
  comm "syz-executor.3", pid 17672, jiffies 4298118891 (age 9.906s)
  hex dump (first 8 bytes):
    00 00 00 00 00 00 00 00                          ........
  backtrace:
    [<ffffffffade5db3e>] kvmalloc_node+0x11e/0x170
    [<ffffffffadd28280>] __cpu_map_entry_alloc+0x2f0/0xb00
    [<ffffffffadd28d8e>] cpu_map_update_elem+0x2fe/0x3d0
    [<ffffffffadc6d0fd>] bpf_map_update_value.isra.0+0x2bd/0x520
    [<ffffffffadc7349b>] map_update_elem+0x4cb/0x720
    [<ffffffffadc7d983>] __se_sys_bpf+0x8c3/0xb90
    [<ffffffffb029cc80>] do_syscall_64+0x30/0x40
    [<ffffffffb0400099>] entry_SYSCALL_64_after_hwframe+0x61/0xc6

In the cpu_map_update_elem flow, when kthread_stop is called before
calling the threadfn of rcpu->kthread, since the KTHREAD_SHOULD_STOP bit
of kthread has been set by kthread_stop, the threadfn of rcpu->kthread
will never be executed, and rcpu->refcnt will never be 0, which will
lead to the allocated rcpu, rcpu->queue and rcpu->queue->queue cannot be
released.

Calling kthread_stop before executing kthread's threadfn will return
-EINTR. We can complete the release of memory resources in this state.

Fixes: 6710e112 ("bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20230711115848.2701559-1-pulehui@huaweicloud.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>