[RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu()

KOSAKI Motohiro
2008-10-23T15:00:19Z

Hi Heiko,

> >> I think the following part of your patch:
> >>
> >>> diff --git a/mm/swap.c b/mm/swap.c
> >>> index fee6b97..bc58c13 100644
> >>> --- a/mm/swap.c
> >>> +++ b/mm/swap.c
> >>> @@ -278,7 +278,7 @@ void lru_add_drain(void)
> >>> put_cpu();
> >>> }
> >>>
> >>> -#ifdef CONFIG_NUMA
> >>> +#if defined(CONFIG_NUMA) || defined(CONFIG_UNEVICTABLE_LRU)
> >>> static void lru_add_drain_per_cpu(struct work_struct *dummy)
> >>> {
> >>> lru_add_drain();
> >>
> >> causes this (allyesconfig on s390):
> >
> > hm,
> >
> > I don't think so.
> >
> > Actually, this patch has
> > mmap_sem -> lru_add_drain_all() dependency.
> >
> > but its dependency already exist in another place.
> > example,
> >
> > sys_move_pages()
> > do_move_pages() <- down_read(mmap_sem)
> > migrate_prep()
> > lru_add_drain_all()
> >
> > Thought?
>
> ok. maybe I understand this issue.
>
> This bug is caused by folloing dependencys.
>
> some VM place has
> mmap_sem -> kevent_wq
>
> net/core/dev.c::dev_ioctl() has
> rtnl_lock -> mmap_sem (*) almost ioctl has
> copy_from_user() and it cause page fault.
>
> linkwatch_event has
> kevent_wq -> rtnl_lock
>
>
> So, I think VM subsystem shouldn't use kevent_wq because many driver
> use ioctl and work queue combination.
> then drivers fixing isn't easy.
>
> I'll make the patch soon.

My box can't reproduce this issue.
Could you please test on following patch?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Heiko reported following lockdep warnings.

=================================================================================
causes this (allyesconfig on s390):

[17179587.988810] =======================================================
[17179587.988819] [ INFO: possible circular locking dependency detected ]
[17179587.988824] 2.6.27-06509-g2515ddc-dirty #190
[17179587.988827] -------------------------------------------------------
[17179587.988831] multipathd/3868 is trying to acquire lock:
[17179587.988834] (events){--..}, at: [<0000000000157f82>] flush_work+0x42/0x124
[17179587.988850]
[17179587.988851] but task is already holding lock:
[17179587.988854] (&mm->mmap_sem){----}, at: [<00000000001c0be4>] sys_mlockall+0x5c/0xe0
[17179587.988865]
[17179587.988866] which lock already depends on the new lock.
[17179587.988867]
[17179587.988871]
[17179587.988871] the existing dependency chain (in reverse order) is:
[17179587.988875]
[17179587.988876] -> #3 (&mm->mmap_sem){----}:
[17179587.988883] [<0000000000171a42>] __lock_acquire+0x143e/0x17c4
[17179587.988891] [<0000000000171e5c>] lock_acquire+0x94/0xbc
[17179587.988896] [<0000000000b2a532>] down_read+0x62/0xd8
[17179587.988905] [<0000000000b2cc40>] do_dat_exception+0x14c/0x390
[17179587.988910] [<0000000000114d36>] sysc_return+0x0/0x8
[17179587.988917] [<00000000006c694a>] copy_from_user_mvcos+0x12/0x84
[17179587.988926] [<00000000007335f0>] eql_ioctl+0x3e8/0x590
[17179587.988935] [<00000000008b6230>] dev_ifsioc+0x29c/0x2c8
[17179587.988942] [<00000000008b6874>] dev_ioctl+0x618/0x680
[17179587.988946] [<00000000008a1a8c>] sock_ioctl+0x2b4/0x2c8
[17179587.988953] [<00000000001f99a8>] vfs_ioctl+0x50/0xbc
[17179587.988960] [<00000000001f9ee2>] do_vfs_ioctl+0x4ce/0x510
[17179587.988965] [<00000000001f9f94>] sys_ioctl+0x70/0x98
[17179587.988970] [<0000000000114d30>] sysc_noemu+0x10/0x16
[17179587.988975] [<0000020000131286>] 0x20000131286
[17179587.988980]
[17179587.988981] -> #2 (rtnl_mutex){--..}:
[17179587.988987] [<0000000000171a42>] __lock_acquire+0x143e/0x17c4
[17179587.988993] [<0000000000171e5c>] lock_acquire+0x94/0xbc
[17179587.988998] [<0000000000b29ae8>] mutex_lock_nested+0x11c/0x31c
[17179587.989003] [<00000000008bff1c>] rtnl_lock+0x30/0x40
[17179587.989009] [<00000000008c144e>] linkwatch_event+0x26/0x6c
[17179587.989015] [<0000000000157356>] run_workqueue+0x146/0x240
[17179587.989020] [<000000000015756e>] worker_thread+0x11e/0x134
[17179587.989025] [<000000000015cd8e>] kthread+0x6e/0xa4
[17179587.989030] [<000000000010ad9a>] kernel_thread_starter+0x6/0xc
[17179587.989036] [<000000000010ad94>] kernel_thread_starter+0x0/0xc
[17179587.989042]
[17179587.989042] -> #1 ((linkwatch_work).work){--..}:
[17179587.989049] [<0000000000171a42>] __lock_acquire+0x143e/0x17c4
[17179587.989054] [<0000000000171e5c>] lock_acquire+0x94/0xbc
[17179587.989059] [<0000000000157350>] run_workqueue+0x140/0x240
[17179587.989064] [<000000000015756e>] worker_thread+0x11e/0x134
[17179587.989069] [<000000000015cd8e>] kthread+0x6e/0xa4
[17179587.989074] [<000000000010ad9a>] kernel_thread_starter+0x6/0xc
[17179587.989079] [<000000000010ad94>] kernel_thread_starter+0x0/0xc
[17179587.989084]
[17179587.989085] -> #0 (events){--..}:
[17179587.989091] [<00000000001716ca>] __lock_acquire+0x10c6/0x17c4
[17179587.989096] [<0000000000171e5c>] lock_acquire+0x94/0xbc
[17179587.989101] [<0000000000157fb4>] flush_work+0x74/0x124
[17179587.989107] [<0000000000158620>] schedule_on_each_cpu+0xec/0x138
[17179587.989112] [<00000000001b0ab4>] lru_add_drain_all+0x2c/0x40
[17179587.989117] [<00000000001c05ac>] __mlock_vma_pages_range+0xcc/0x2e8
[17179587.989123] [<00000000001c0970>] mlock_fixup+0x1a8/0x280
[17179587.989128] [<00000000001c0aec>] do_mlockall+0xa4/0xd4
[17179587.989133] [<00000000001c0c36>] sys_mlockall+0xae/0xe0
[17179587.989138] [<0000000000114d30>] sysc_noemu+0x10/0x16
[17179587.989142] [<000002000025a466>] 0x2000025a466
[17179587.989147]
[17179587.989148] other info that might help us debug this:
[17179587.989149]
[17179587.989154] 1 lock held by multipathd/3868:
[17179587.989156] #0: (&mm->mmap_sem){----}, at: [<00000000001c0be4>] sys_mlockall+0x5c/0xe0
[17179587.989165]
[17179587.989166] stack backtrace:
[17179587.989170] CPU: 0 Not tainted 2.6.27-06509-g2515ddc-dirty #190
[17179587.989174] Process multipathd (pid: 3868, task: 000000003978a298, ksp: 0000000039b23eb8)
[17179587.989178] 000000003978aa00 0000000039b238b8 0000000000000002 0000000000000000
[17179587.989184] 0000000039b23958 0000000039b238d0 0000000039b238d0 00000000001060ee
[17179587.989192] 0000000000000003 0000000000000000 0000000000000000 000000000000000b
[17179587.989199] 0000000000000060 0000000000000008 0000000039b238b8 0000000039b23928
[17179587.989207] 0000000000b30b50 00000000001060ee 0000000039b238b8 0000000039b23910
[17179587.989216] Call Trace:
[17179587.989219] ([<0000000000106036>] show_trace+0xb2/0xd0)
[17179587.989225] [<000000000010610c>] show_stack+0xb8/0xc8
[17179587.989230] [<0000000000b27a96>] dump_stack+0xae/0xbc
[17179587.989234] [<000000000017019e>] print_circular_bug_tail+0xee/0x100
[17179587.989240] [<00000000001716ca>] __lock_acquire+0x10c6/0x17c4
[17179587.989245] [<0000000000171e5c>] lock_acquire+0x94/0xbc
[17179587.989250] [<0000000000157fb4>] flush_work+0x74/0x124
[17179587.989256] [<0000000000158620>] schedule_on_each_cpu+0xec/0x138
[17179587.989261] [<00000000001b0ab4>] lru_add_drain_all+0x2c/0x40
[17179587.989266] [<00000000001c05ac>] __mlock_vma_pages_range+0xcc/0x2e8
[17179587.989271] [<00000000001c0970>] mlock_fixup+0x1a8/0x280
[17179587.989276] [<00000000001c0aec>] do_mlockall+0xa4/0xd4
[17179587.989281] [<00000000001c0c36>] sys_mlockall+0xae/0xe0
[17179587.989286] [<0000000000114d30>] sysc_noemu+0x10/0x16
[17179587.989290] [<000002000025a466>] 0x2000025a466
[17179587.989294] INFO: lockdep is turned off.
=======================================================================================

It because following three circular locking dependency.

Some VM place has
mmap_sem -> kevent_wq via lru_add_drain_all()

net/core/dev.c::dev_ioctl() has
rtnl_lock -> mmap_sem (*) the ioctl has copy_from_user() and it can do page fault.

linkwatch_event has
kevent_wq -> rtnl_lock

Actually, schedule_on_each_cpu() is very problematic function.
it introduce the dependency of all worker on keventd_wq,
but we can't know what lock held by worker in kevend_wq because
keventd_wq is widely used out of kernel drivers too.

So, the task of any lock held shouldn't wait on keventd_wq.
Its task should use own special purpose work queue.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
CC: Christoph Lameter <cl@linux-foundation.org>
CC: Nick Piggin <npiggin@suse.de>
CC: Hugh Dickins <hugh@veritas.com>,
CC: Andrew Morton <akpm@linux-foundation.org>,
CC: Linus Torvalds <torvalds@linux-foundation.org>,
CC: Rik van Riel <riel@redhat.com>,
CC: Lee Schermerhorn <lee.schermerhorn@hp.com>,

linux-2.6.27-git10-vm_wq/include/linux/workqueue.h | 1
linux-2.6.27-git10-vm_wq/kernel/workqueue.c | 37 +++++++++++++++++++++
linux-2.6.27-git10-vm_wq/mm/swap.c | 8 +++-
3 files changed, 45 insertions(+), 1 deletion(-)

Index: linux-2.6.27-git10-vm_wq/include/linux/workqueue.h
===================================================================
--- linux-2.6.27-git10-vm_wq.orig/include/linux/workqueue.h 2008-10-23 21:01:38.000000000 +0900
+++ linux-2.6.27-git10-vm_wq/include/linux/workqueue.h 2008-10-23 22:34:20.000000000 +0900
@@ -195,6 +195,7 @@ extern int schedule_delayed_work(struct
extern int schedule_delayed_work_on(int cpu, struct delayed_work *work,
unsigned long delay);
extern int schedule_on_each_cpu(work_func_t func);
+int queue_work_on_each_cpu(struct workqueue_struct *wq, work_func_t func);
extern int current_is_keventd(void);
extern int keventd_up(void);

Index: linux-2.6.27-git10-vm_wq/kernel/workqueue.c
===================================================================
--- linux-2.6.27-git10-vm_wq.orig/kernel/workqueue.c 2008-10-23 21:01:38.000000000 +0900
+++ linux-2.6.27-git10-vm_wq/kernel/workqueue.c 2008-10-23 22:34:20.000000000 +0900
@@ -674,6 +674,8 @@ EXPORT_SYMBOL(schedule_delayed_work_on);
* Returns -ve errno on failure.
*
* schedule_on_each_cpu() is very slow.
+ * caller should NOT held any lock, otherwise flush_work(keventd_wq) can
+ * cause dead-lock.
*/
int schedule_on_each_cpu(work_func_t func)
{
@@ -698,6 +700,41 @@ int schedule_on_each_cpu(work_func_t fun
return 0;
}

+/**
+ * queue_work_on_each_cpu - call a function on each online CPU
+ *
+ * @wq: the workqueue
+ * @func: the function to call
+ *
+ * Returns zero on success.
+ * Returns -ve errno on failure.
+ *
+ * similar to schedule_on_each_cpu(), but wq argument is there.
+ * queue_work_on_each_cpu() is very slow.
+ */
+int queue_work_on_each_cpu(struct workqueue_struct *wq, work_func_t func)
+{
+ int cpu;
+ struct work_struct *works;
+
+ works = alloc_percpu(struct work_struct);
+ if (!works)
+ return -ENOMEM;
+
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ struct work_struct *work = per_cpu_ptr(works, cpu);
+
+ INIT_WORK(work, func);
+ queue_work_on(cpu, wq, work);
+ }
+ for_each_online_cpu(cpu)
+ flush_work(per_cpu_ptr(works, cpu));
+ put_online_cpus();
+ free_percpu(works);
+ return 0;
+}
+
void flush_scheduled_work(void)
{
flush_workqueue(keventd_wq);
Index: linux-2.6.27-git10-vm_wq/mm/swap.c
===================================================================
--- linux-2.6.27-git10-vm_wq.orig/mm/swap.c 2008-10-23 21:01:38.000000000 +0900
+++ linux-2.6.27-git10-vm_wq/mm/swap.c 2008-10-23 22:53:27.000000000 +0900
@@ -39,6 +39,8 @@ int page_cluster;
static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);

+static struct workqueue_struct *vm_wq __read_mostly;
+
/*
* This path almost never happens for VM activity - pages are normally
* freed via pagevecs. But it gets used by networking.
@@ -310,7 +312,7 @@ static void lru_add_drain_per_cpu(struct
*/
int lru_add_drain_all(void)
{
- return schedule_on_each_cpu(lru_add_drain_per_cpu);
+ return queue_work_on_each_cpu(vm_wq, lru_add_drain_per_cpu);
}

#else
@@ -611,4 +613,8 @@ void __init swap_setup(void)
#ifdef CONFIG_HOTPLUG_CPU
hotcpu_notifier(cpu_swap_callback, 0);
#endif
+
+ vm_wq = create_workqueue("vm_work");
+ BUG_ON(!vm_wq);
+
}