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SubjectRe: [PATCH] mm/memory-hotplug: Switch locking to a percpu rwsem
On Fri, 30 Jun 2017, Andrey Ryabinin wrote:
> On 06/30/2017 01:15 PM, Thomas Gleixner wrote:
> > On Fri, 30 Jun 2017, Michal Hocko wrote:
> >> So I like this simplification a lot! Even if we can get rid of the
> >> stop_machine eventually this patch would be an improvement. A short
> >> comment on why the per-cpu semaphore over the regular one is better
> >> would be nice.
> >
> > Yes, will add one.
> >
> > The main point is that the current locking construct is evading lockdep due
> > to the ability to support recursive locking, which I did not observe so
> > far.
> >
>
> Like this?

Cute.....

> [ 131.023034] Call Trace:
> [ 131.023034] dump_stack+0x85/0xc7
> [ 131.023034] __lock_acquire+0x1747/0x17a0
> [ 131.023034] ? lru_add_drain_all+0x3d/0x190
> [ 131.023034] ? __mutex_lock+0x218/0x940
> [ 131.023034] ? trace_hardirqs_on+0xd/0x10
> [ 131.023034] lock_acquire+0x103/0x200
> [ 131.023034] ? lock_acquire+0x103/0x200
> [ 131.023034] ? lru_add_drain_all+0x42/0x190
> [ 131.023034] cpus_read_lock+0x3d/0x80
> [ 131.023034] ? lru_add_drain_all+0x42/0x190
> [ 131.023034] lru_add_drain_all+0x42/0x190
> [ 131.023034] __offline_pages.constprop.25+0x5de/0x870
> [ 131.023034] offline_pages+0xc/0x10
> [ 131.023034] memory_subsys_offline+0x43/0x70
> [ 131.023034] device_offline+0x83/0xb0
> [ 131.023034] store_mem_state+0xdb/0xe0
> [ 131.023034] dev_attr_store+0x13/0x20
> [ 131.023034] sysfs_kf_write+0x40/0x50
> [ 131.023034] kernfs_fop_write+0x130/0x1b0
> [ 131.023034] __vfs_write+0x23/0x130
> [ 131.023034] ? rcu_read_lock_sched_held+0x6d/0x80
> [ 131.023034] ? rcu_sync_lockdep_assert+0x2a/0x50
> [ 131.023034] ? __sb_start_write+0xd4/0x1c0
> [ 131.023034] ? vfs_write+0x1a8/0x1d0
> [ 131.023034] vfs_write+0xc8/0x1d0
> [ 131.023034] SyS_write+0x44/0xa0

Why didn't trigger that here? Bah, I should have become suspicious due to
not seeing a splat ....

The patch below should cure that.

Thanks,

tglx

8<-------------------
Subject: mm: Change cpuhotplug lock order in lru_add_drain_all()
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 30 Jun 2017 14:25:24 +0200

Not-Yet-Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/swap.h | 1 +
mm/memory_hotplug.c | 4 ++--
mm/swap.c | 11 ++++++++---
3 files changed, 11 insertions(+), 5 deletions(-)

Index: b/include/linux/swap.h
===================================================================
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -277,6 +277,7 @@ extern void mark_page_accessed(struct pa
extern void lru_add_drain(void);
extern void lru_add_drain_cpu(int cpu);
extern void lru_add_drain_all(void);
+extern void lru_add_drain_all_cpuslocked(void);
extern void rotate_reclaimable_page(struct page *page);
extern void deactivate_file_page(struct page *page);
extern void mark_page_lazyfree(struct page *page);
Index: b/mm/memory_hotplug.c
===================================================================
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1860,7 +1860,7 @@ static int __ref __offline_pages(unsigne
goto failed_removal;
ret = 0;
if (drain) {
- lru_add_drain_all();
+ lru_add_drain_all_cpuslocked();
cond_resched();
drain_all_pages(zone);
}
@@ -1881,7 +1881,7 @@ static int __ref __offline_pages(unsigne
}
}
/* drain all zone's lru pagevec, this is asynchronous... */
- lru_add_drain_all();
+ lru_add_drain_all_cpuslocked();
yield();
/* drain pcp pages, this is synchronous. */
drain_all_pages(zone);
Index: b/mm/swap.c
===================================================================
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -687,7 +687,7 @@ static void lru_add_drain_per_cpu(struct

static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);

-void lru_add_drain_all(void)
+void lru_add_drain_all_cpuslocked(void)
{
static DEFINE_MUTEX(lock);
static struct cpumask has_work;
@@ -701,7 +701,6 @@ void lru_add_drain_all(void)
return;

mutex_lock(&lock);
- get_online_cpus();
cpumask_clear(&has_work);

for_each_online_cpu(cpu) {
@@ -721,10 +720,16 @@ void lru_add_drain_all(void)
for_each_cpu(cpu, &has_work)
flush_work(&per_cpu(lru_add_drain_work, cpu));

- put_online_cpus();
mutex_unlock(&lock);
}

+void lru_add_drain_all(void)
+{
+ get_online_cpus();
+ lru_add_drain_all_cpuslocked();
+ put_online_cpus();
+}
+
/**
* release_pages - batched put_page()
* @pages: array of pages to release
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