Re: Re: [patch] mm, oom: prevent additional oom kills before memory is freed

From: Tetsuo Handa
Date: Sat Jun 17 2017 - 09:30:58 EST

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Michal Hocko wrote:
> On Fri 16-06-17 23:26:20, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Fri 16-06-17 19:27:19, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > > > On Fri 16-06-17 09:54:34, Tetsuo Handa wrote:
> > > > > [...]
> > > > > > And the patch you proposed is broken.
> > > > >
> > > > > Thanks for your testing!
> > > > >
> > > > > > ----------
> > > > > > [ 161.846202] Out of memory: Kill process 6331 (a.out) score 999 or sacrifice child
> > > > > > [ 161.850327] Killed process 6331 (a.out) total-vm:4172kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
> > > > > > [ 161.858503] ------------[ cut here ]------------
> > > > > > [ 161.861512] kernel BUG at mm/memory.c:1381!
> > > > >
> > > > > BUG_ON(addr >= end) suggests our vma has trimmed. I guess I see what is
> > > > > going on here.
> > > > > __oom_reap_task_mm exit_mmap
> > > > > free_pgtables
> > > > > up_write(mm->mmap_sem)
> > > > > down_read_trylock(&mm->mmap_sem)
> > > > > remove_vma
> > > > > unmap_page_range
> > > > >
> > > > > So we need to extend the mmap_sem coverage. See the updated diff (not
> > > > > the full proper patch yet).
> > > >
> > > > That diff is still wrong. We need to prevent __oom_reap_task_mm() from calling
> > > > unmap_page_range() when __mmput() already called exit_mm(), by setting/checking
> > > > MMF_OOM_SKIP like shown below.
> > >
> > > Care to explain why?
> >
> > I don't know. Your updated diff is causing below oops.
> >
> > ----------
> > [ 90.621890] Out of memory: Kill process 2671 (a.out) score 999 or sacrifice child
> > [ 90.624636] Killed process 2671 (a.out) total-vm:4172kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
> > [ 90.861308] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> > [ 90.863695] Modules linked in: coretemp pcspkr sg vmw_vmci shpchp i2c_piix4 sd_mod ata_generic pata_acpi serio_raw vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm mptspi scsi_transport_spi mptscsih ahci mptbase libahci drm e1000 ata_piix i2c_core libata ipv6
> > [ 90.870672] CPU: 2 PID: 47 Comm: oom_reaper Not tainted 4.12.0-rc5+ #128
> > [ 90.872929] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
> > [ 90.875995] task: ffff88007b6cd2c0 task.stack: ffff88007b6d0000
> > [ 90.878290] RIP: 0010:__oom_reap_task_mm+0xa1/0x160
>
> What does this dissassemble to on your kernel? Care to post addr2line?

----------
[ 114.427451] Out of memory: Kill process 2876 (a.out) score 999 or sacrifice child
[ 114.430208] Killed process 2876 (a.out) total-vm:4172kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
[ 114.436753] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 114.439129] Modules linked in: pcspkr coretemp sg vmw_vmci i2c_piix4 shpchp sd_mod ata_generic pata_acpi serio_raw vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm ahci e1000 libahci mptspi scsi_transport_spi drm mptscsih mptbase i2c_core ata_piix libata ipv6
[ 114.446220] CPU: 0 PID: 47 Comm: oom_reaper Not tainted 4.12.0-rc5+ #133
[ 114.448705] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
[ 114.451695] task: ffff88007b6cd2c0 task.stack: ffff88007b6d0000
[ 114.453703] RIP: 0010:__oom_reap_task_mm+0xa1/0x160
[ 114.455422] RSP: 0000:ffff88007b6d3df0 EFLAGS: 00010202
[ 114.457527] RAX: 6b6b6b6b6b6b6b6b RBX: ffff8800670eaa40 RCX: 0000000000000000
[ 114.460002] RDX: ffff88007b6d3e18 RSI: ffff8800670eaa40 RDI: ffff88007b6d3df0
[ 114.462206] RBP: ffff88007b6d3e98 R08: ffff88007b6cdb08 R09: ffff88007b6cdad0
[ 114.464390] R10: 0000000000000000 R11: 0000000083f54a84 R12: ffff8800670eab00
[ 114.466659] R13: ffff880067211bc0 R14: 6b6b6b6b6b6b6b6b R15: ffff8800670eaa40
[ 114.469126] FS: 0000000000000000(0000) GS:ffff88007c200000(0000) knlGS:0000000000000000
[ 114.471496] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 114.473540] CR2: 00007f55d759d050 CR3: 0000000079ff4000 CR4: 00000000001406f0
[ 114.475773] Call Trace:
[ 114.477078] oom_reaper+0xa2/0x1b0 /* oom_reap_task at mm/oom_kill.c:542 (inlined by) oom_reaper at mm/oom_kill.c:580 */
[ 114.478569] ? wake_up_bit+0x30/0x30
[ 114.480058] kthread+0x10d/0x140
[ 114.481656] ? __oom_reap_task_mm+0x160/0x160
[ 114.483308] ? kthread_create_on_node+0x60/0x60
[ 114.485075] ret_from_fork+0x27/0x40
[ 114.486620] Code: c3 e8 54 82 f1 ff f0 80 8b 7a 04 00 00 40 48 8d bd 58 ff ff ff 48 83 c9 ff 31 d2 48 89 de e8 57 12 03 00 4c 8b 33 4d 85 f6 74 3b <49> 8b 46 50 a9 00 24 40 00 75 27 49 83 be 90 00 00 00 00 74 04
[ 114.491819] RIP: __oom_reap_task_mm+0xa1/0x160 RSP: ffff88007b6d3df0
[ 114.494520] ---[ end trace e254efa6cf6f5fe6 ]---
----------

The __oom_reap_task_mm+0xa1/0x160 is __oom_reap_task_mm at mm/oom_kill.c:472
which is "struct vm_area_struct *vma;" line in __oom_reap_task_mm().
The __oom_reap_task_mm+0xb1/0x160 is __oom_reap_task_mm at mm/oom_kill.c:519
which is "if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))" line.
The <49> 8b 46 50 is "vma->vm_flags" in can_madv_dontneed_vma(vma) from __oom_reap_task_mm().

Is it safe for the OOM reaper to call tlb_gather_mmu()/unmap_page_range()/tlb_finish_mmu() sequence
after the OOM victim already completed tlb_gather_mmu()/unmap_vmas()/free_pgtables()/tlb_finish_mmu()/
remove_vma() sequence from exit_mmap() from __mmput() from mmput() from exit_mm() from do_exit() ?
I guess we need to prevent the OOM reaper from calling the sequence if the OOM victim already did
the sequence. And my patch did it via trial and error.

----------
unlock_oom:
mutex_unlock(&oom_lock);
26a: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
271: e8 00 00 00 00 callq 276 <__oom_reap_task_mm+0x56>
return ret;
}
276: 48 8b 55 d8 mov -0x28(%rbp),%rdx
27a: 65 48 33 14 25 28 00 xor %gs:0x28,%rdx
281: 00 00
283: 89 d8 mov %ebx,%eax
285: 75 10 jne 297 <__oom_reap_task_mm+0x77>
287: 48 81 c4 88 00 00 00 add $0x88,%rsp
28e: 5b pop %rbx
28f: 41 5c pop %r12
291: 41 5d pop %r13
293: 41 5e pop %r14
295: 5d pop %rbp
296: c3 retq
297: e8 00 00 00 00 callq 29c <__oom_reap_task_mm+0x7c>
*/
static __always_inline void
set_bit(long nr, volatile unsigned long *addr)
{
if (IS_IMMEDIATE(nr)) {
asm volatile(LOCK_PREFIX "orb %1,%0"
29c: f0 80 8b 7a 04 00 00 lock orb $0x40,0x47a(%rbx)
2a3: 40
* should imply barriers already and the reader would hit a page fault
* if it stumbled over a reaped memory.
*/
set_bit(MMF_UNSTABLE, &mm->flags);

tlb_gather_mmu(&tlb, mm, 0, -1);
2a4: 48 8d bd 58 ff ff ff lea -0xa8(%rbp),%rdi
2ab: 48 83 c9 ff or $0xffffffffffffffff,%rcx
2af: 31 d2 xor %edx,%edx
2b1: 48 89 de mov %rbx,%rsi
2b4: e8 00 00 00 00 callq 2b9 <__oom_reap_task_mm+0x99>
for (vma = mm->mmap ; vma; vma = vma->vm_next) {
2b9: 4c 8b 33 mov (%rbx),%r14
2bc: 4d 85 f6 test %r14,%r14
2bf: 74 3b je 2fc <__oom_reap_task_mm+0xdc>
static DEFINE_SPINLOCK(oom_reaper_lock);

static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
{
struct mmu_gather tlb;
struct vm_area_struct *vma;
2c1: 49 8b 46 50 mov 0x50(%r14),%rax
*/
set_bit(MMF_UNSTABLE, &mm->flags);

tlb_gather_mmu(&tlb, mm, 0, -1);
for (vma = mm->mmap ; vma; vma = vma->vm_next) {
if (!can_madv_dontneed_vma(vma))
2c5: a9 00 24 40 00 test $0x402400,%eax
2ca: 75 27 jne 2f3 <__oom_reap_task_mm+0xd3>
* We do not even care about fs backed pages because all
* which are reclaimable have already been reclaimed and
* we do not want to block exit_mmap by keeping mm ref
* count elevated without a good reason.
*/
if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
2cc: 49 83 be 90 00 00 00 cmpq $0x0,0x90(%r14)
2d3: 00
2d4: 74 04 je 2da <__oom_reap_task_mm+0xba>
2d6: a8 08 test $0x8,%al
2d8: 75 19 jne 2f3 <__oom_reap_task_mm+0xd3>
unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
2da: 49 8b 4e 08 mov 0x8(%r14),%rcx
2de: 49 8b 16 mov (%r14),%rdx
2e1: 48 8d bd 58 ff ff ff lea -0xa8(%rbp),%rdi
2e8: 45 31 c0 xor %r8d,%r8d
2eb: 4c 89 f6 mov %r14,%rsi
2ee: e8 00 00 00 00 callq 2f3 <__oom_reap_task_mm+0xd3>
* if it stumbled over a reaped memory.
----------

Next message: Vinod Koul: "Re: [PATCH] dmaengine: qcom-bam: Process multiple pending descriptors"
Previous message: Sudip Mukherjee: "[PATCH] parport_serial: Add support for WCH CH382L PCI-E single parallel port card."
In reply to: Michal Hocko: "Re: Re: [patch] mm, oom: prevent additional oom kills before memoryis freed"
Next in thread: Michal Hocko: "Re: Re: [patch] mm, oom: prevent additional oom kills before memory is freed"
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