The patch titled
Subject: Revert mm/vmstat.c: fix vmstat_update() preemption BUG
has been added to the -mm tree. Its filename is
revert-mm-vmstatc-fix-vmstat_update-preemption-bug.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/revert-mm-vmstatc-fix-vmstat_update-preemption-bug.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/revert-mm-vmstatc-fix-vmstat_update-preemption-bug.patch
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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: Revert mm/vmstat.c: fix vmstat_update() preemption BUG
Revert c7f26ccfb2c3 ("mm/vmstat.c: fix vmstat_update() preemption BUG").
Steven saw a "using smp_processor_id() in preemptible" message and added a
preempt_disable() section around it to keep it quiet. This is not the
right thing to do it does not fix the real problem.
vmstat_update() is invoked by a kworker on a specific CPU. This worker it
bound to this CPU. The name of the worker was "kworker/1:1" so it should
have been a worker which was bound to CPU1. A worker which can run on any
CPU would have a `u' before the first digit.
smp_processor_id() can be used in a preempt-enabled region as long as the
task is bound to a single CPU which is the case here. If it could run on
an arbitrary CPU then this is the problem we have an should seek to
resolve.
Not only this smp_processor_id() must not be migrated to another CPU but
also refresh_cpu_vm_stats() which might access wrong per-CPU variables.
Not to mention that other code relies on the fact that such a worker runs
on one specific CPU only.
Therefore revert that commit and we should look instead what broke the
affinity mask of the kworker.
Link: http://lkml.kernel.org/r/20180504104451.20278-1-bigeasy@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Steven J. Hill <steven.hill@xxxxxxxxxx>
Cc: Tejun Heo <htejun@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmstat.c | 2 --
1 file changed, 2 deletions(-)
diff -puN mm/vmstat.c~revert-mm-vmstatc-fix-vmstat_update-preemption-bug mm/vmstat.c
--- a/mm/vmstat.c~revert-mm-vmstatc-fix-vmstat_update-preemption-bug
+++ a/mm/vmstat.c
@@ -1796,11 +1796,9 @@ static void vmstat_update(struct work_st
* 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();
}
}
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
lib-percpu_idac-dont-do-alloc-from-per-cpu-list-if-there-is-none.patch
revert-mm-vmstatc-fix-vmstat_update-preemption-bug.patch
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