mm/vmstat.c: fix vmstat_update() preemption BUG

Attempting to hotplug CPUs with CONFIG_VM_EVENT_COUNTERS enabled can
cause vmstat_update() to report a BUG due to preemption not being
disabled around smp_processor_id().

Discovered on Ubiquiti EdgeRouter Pro with Cavium Octeon II processor.

  BUG: using smp_processor_id() in preemptible [00000000] code:
  kworker/1:1/269
  caller is vmstat_update+0x50/0xa0
  CPU: 0 PID: 269 Comm: kworker/1:1 Not tainted
  4.16.0-rc4-Cavium-Octeon-00009-gf83bbd5-dirty #1
  Workqueue: mm_percpu_wq vmstat_update
  Call Trace:
    show_stack+0x94/0x128
    dump_stack+0xa4/0xe0
    check_preemption_disabled+0x118/0x120
    vmstat_update+0x50/0xa0
    process_one_work+0x144/0x348
    worker_thread+0x150/0x4b8
    kthread+0x110/0x140
    ret_from_kernel_thread+0x14/0x1c

Link: http://lkml.kernel.org/r/1520881552-25659-1-git-send-email-steven.hill@cavium.com
Signed-off-by: Steven J. Hill <steven.hill@cavium.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 40b2db6db6b16df89ff5c313cab83c95b8c0f38e..33581be705f03ee97527ad61921c3339a05524d0 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1839,9 +1839,11 @@ static void vmstat_update(struct work_struct *w)
                 * to occur in the future. Keep on running the
                 * update worker thread.
                 */
+               preempt_disable();
                queue_delayed_work_on(smp_processor_id(), mm_percpu_wq,
                                this_cpu_ptr(&vmstat_work),
                                round_jiffies_relative(sysctl_stat_interval));
+               preempt_enable();
        }
 }