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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Michal Hocko <mhocko@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"David Rientjes" <rientjes@google.com>,
	"Christian König" <christian.koenig@amd.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Masahiro Yamada" <yamada.masahiro@socionext.com>,
	"Wei Wang" <wvw@google.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Jann Horn" <jannh@google.com>, "Feng Tang" <feng.tang@intel.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end()
Date: Thu, 15 Aug 2019 17:13:23 -0300
Message-ID: <20190815201323.GU21596@ziepe.ca> (raw)
In-Reply-To: <20190815193526.GT9477@dhcp22.suse.cz>

On Thu, Aug 15, 2019 at 09:35:26PM +0200, Michal Hocko wrote:

> > The last detail is I'm still unclear what a GFP flags a blockable
> > invalidate_range_start() should use. Is GFP_KERNEL OK?
> 
> I hope I will not make this muddy again ;)
> invalidate_range_start in the blockable mode can use/depend on any sleepable
> allocation allowed in the context it is called from. 

'in the context is is called from' is the magic phrase, as
invalidate_range_start is called while holding several different mm
related locks. I know at least write mmap_sem and i_mmap_rwsem
(write?)

Can GFP_KERNEL be called while holding those locks?

This is the question of indirect dependency on reclaim via locks you
raised earlier.

> So in other words it is no different from any other function in the
> kernel that calls into allocator. As the API is missing gfp context
> then I hope it is not called from any restricted contexts (except
> from the oom which we have !blockable for).

Yes, the callers are exactly my concern.
 
> > Lockdep has
> > complained on that in past due to fs_reclaim - how do you know if it
> > is a false positive?
> 
> I would have to see the specific lockdep splat.

See below. I found it when trying to understand why the registration
of the mmu notififer was so oddly coded.

The situation was:

  down_write(&mm->mmap_sem);
  mm_take_all_locks(mm);
  kmalloc(GFP_KERNEL);  <--- lockdep warning

I understood Daniel said he saw this directly on a recent kernel when
working with his lockdep patch?

Checking myself, on todays kernel I see a call chain:

shrink_all_memory
  fs_reclaim_acquire(sc.gfp_mask);
  [..]
  do_try_to_free_pages
   shrink_zones
    shrink_node
     shrink_node_memcg
      shrink_list
       shrink_active_list
        page_referenced
         rmap_walk
          rmap_walk_file
           i_mmap_lock_read
            down_read(i_mmap_rwsem)

So it is possible that the down_read() above will block on
i_mmap_rwsem being held in the caller of invalidate_range_start which
is doing kmalloc(GPF_KERNEL).

Is this OK? The lockdep annotation says no..

Jason

commit 35cfa2b0b491c37e23527822bf365610dbb188e5
Author: Gavin Shan <shangw@linux.vnet.ibm.com>
Date:   Thu Oct 25 13:38:01 2012 -0700

    mm/mmu_notifier: allocate mmu_notifier in advance
    
    While allocating mmu_notifier with parameter GFP_KERNEL, swap would start
    to work in case of tight available memory.  Eventually, that would lead to
    a deadlock while the swap deamon swaps anonymous pages.  It was caused by
    commit e0f3c3f78da29b ("mm/mmu_notifier: init notifier if necessary").
    
      =================================
      [ INFO: inconsistent lock state ]
      3.7.0-rc1+ #518 Not tainted
      ---------------------------------
      inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
      kswapd0/35 [HC0[0]:SC0[0]:HE1:SE1] takes:
       (&mapping->i_mmap_mutex){+.+.?.}, at: page_referenced+0x9c/0x2e0
      {RECLAIM_FS-ON-W} state was registered at:
         mark_held_locks+0x86/0x150
         lockdep_trace_alloc+0x67/0xc0
         kmem_cache_alloc_trace+0x33/0x230
         do_mmu_notifier_register+0x87/0x180
         mmu_notifier_register+0x13/0x20
         kvm_dev_ioctl+0x428/0x510
         do_vfs_ioctl+0x98/0x570
         sys_ioctl+0x91/0xb0
         system_call_fastpath+0x16/0x1b


  reply index

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14 20:20 [PATCH 0/5] hmm & mmu_notifier debug/lockdep annotations Daniel Vetter
2019-08-14 20:20 ` [PATCH 1/5] mm: Check if mmu notifier callbacks are allowed to fail Daniel Vetter
2019-08-14 22:14   ` Andrew Morton
2019-08-14 23:22     ` Jason Gunthorpe
2019-08-14 23:34     ` Ralph Campbell
2019-08-16 17:19   ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 2/5] kernel.h: Add non_block_start/end() Daniel Vetter
2019-08-14 20:45   ` Andrew Morton
2019-08-15  6:52     ` Daniel Vetter
2019-08-15  8:44     ` Michal Hocko
2019-08-15 13:04       ` Jason Gunthorpe
2019-08-15 13:12         ` Daniel Vetter
2019-08-15 14:37           ` Jason Gunthorpe
2019-08-15 14:43             ` Daniel Vetter
2019-08-15 15:10               ` Jason Gunthorpe
2019-08-15 16:25                 ` Daniel Vetter
2019-08-15 17:35                   ` Jason Gunthorpe
2019-08-15 17:39                     ` Jerome Glisse
2019-08-15 18:01                       ` Jason Gunthorpe
2019-08-15 18:27                         ` Jerome Glisse
2019-08-15 18:57                           ` Jason Gunthorpe
2019-08-15 16:32                 ` Jerome Glisse
2019-08-15 17:16                   ` Jason Gunthorpe
2019-08-15 17:21                     ` Daniel Vetter
2019-08-15 17:35                       ` Jerome Glisse
2019-08-15 13:24         ` Michal Hocko
2019-08-15 22:15       ` Andrew Morton
2019-08-16  8:24         ` Michal Hocko
2019-08-14 23:58   ` Jason Gunthorpe
2019-08-15  6:58     ` Daniel Vetter
2019-08-15 12:23       ` Jason Gunthorpe
2019-08-15 13:21         ` Michal Hocko
2019-08-15 14:12           ` Jason Gunthorpe
2019-08-15 16:00             ` Michal Hocko
2019-08-15 16:56               ` Jason Gunthorpe
2019-08-15 17:11                 ` Jerome Glisse
2019-08-15 17:17                   ` Jason Gunthorpe
2019-08-15 17:42                 ` Michal Hocko
2019-08-15 17:57                   ` Jerome Glisse
2019-08-15 18:24                   ` Jason Gunthorpe
2019-08-15 19:05                     ` Michal Hocko
2019-08-15 19:18                       ` Jason Gunthorpe
2019-08-15 19:35                         ` Michal Hocko
2019-08-15 20:13                           ` Jason Gunthorpe [this message]
2019-08-16  8:10                             ` Michal Hocko
2019-08-16 12:19                               ` Jason Gunthorpe
2019-08-16 12:26                                 ` Michal Hocko
2019-08-15 20:16                           ` [Intel-gfx] " Daniel Vetter
2019-08-15 20:27                             ` Jason Gunthorpe
2019-08-15 20:49                               ` Daniel Vetter
2019-08-16  1:00                                 ` Jason Gunthorpe
2019-08-16  6:20                                   ` Daniel Vetter
2019-08-16 12:12                                     ` Jason Gunthorpe
2019-08-16 14:11                                       ` Daniel Vetter
2019-08-16 14:38                                         ` Jason Gunthorpe
2019-08-16 16:36                                           ` Daniel Vetter
2019-08-16 16:54                                             ` Jason Gunthorpe
2019-08-16  8:27                             ` Michal Hocko
2019-08-14 20:20 ` [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable Daniel Vetter
2019-08-15  0:00   ` Jason Gunthorpe
2019-08-15  7:02     ` Daniel Vetter
     [not found]       ` <20190815123556.GB21596@ziepe.ca>
2019-08-17 16:09         ` Daniel Vetter
2019-08-14 20:20 ` [PATCH 4/5] mm, notifier: Add a lockdep map for invalidate_range_start Daniel Vetter
2019-08-15  0:09   ` Jason Gunthorpe
2019-08-15  7:10     ` Daniel Vetter
2019-08-15 12:53       ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device_pagetables errors Daniel Vetter
2019-08-15  0:11   ` Jason Gunthorpe
2019-08-15  7:14     ` Daniel Vetter

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