Re: mlock: mlocked pages are unevictable

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2008-10-22 at 02:18 +0900, KOSAKI Motohiro wrote:
> 2008/10/22 KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>:
> > Hi
> >
> >> 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):

I would have suspected the new might_fault() annotation, although I
haven't checked if that made it to Linus yet.

> > 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.

Doing what exactly?

The problem appears to be calling flush_work(), which is rather heavy
handed. We could do schedule_on_each_cpu() using a completion.

Which I think is a nicer solution (if sufficient of course).

lockdep splat attached for Oleg's convenience.

> [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.