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SubjectRe: kernel 3.0: BUG: soft lockup: find_get_pages+0x51/0x110
[ Subject refers to a different, unexplained 3.0 bug from Pawel ]

On Wed, 12 Oct 2011, Pawel Sikora wrote:

> Hi Hugh,
> i'm resending previous private email with larger cc list as you've requested.

Thanks, yes, on this one I think I do have an answer;
and we ought to bring Mel and Andrea in too.

>
> in the last weekend my server died again (processes stuck for 22/23s!) but this time i have more logs for you.
>
> on my dual-opteron machines i have non-standard settings:
> - DISABLED swap space (fast user process killing is better for my autotest farm than long disk swapping
> and 64GB ecc-ram is enough for my processing).
> - vm.overcommit_memory = 2,
> - vm.overcommit_ratio = 100.
>
> after initial BUG_ON (pasted below) there's a flood of 'rcu_sched_state detected stalls / CPU#X stuck for 22s!'

Yes, those are just a tiresome consequence of exiting from a BUG
while holding the page table lock(s).

> (full compressed log is available at: http://pluto.agmk.net/kernel/kernel.bz2)
>
> Oct 9 08:06:43 hal kernel: [408578.629070] ------------[ cut here ]------------
> Oct 9 08:06:43 hal kernel: [408578.629143] kernel BUG at include/linux/swapops.h:105!
> Oct 9 08:06:43 hal kernel: [408578.629143] invalid opcode: 0000 [#1] SMP
> Oct 9 08:06:43 hal kernel: [408578.629143] CPU 14
[ I'm deleting that irrelevant long line list of modules ]
> Oct 9 08:06:43 hal kernel: [408578.629143]
> Oct 9 08:06:43 hal kernel: [408578.629143] Pid: 29214, comm: bitgen Not tainted 3.0.4 #5 Supermicro H8DGU/H8DGU
> Oct 9 08:06:43 hal kernel: [408578.629143] RIP: 0010:[<ffffffff81127b76>] [<ffffffff81127b76>] migration_entry_wait+0x156/0x160
> Oct 9 08:06:43 hal kernel: [408578.629143] RSP: 0000:ffff88021cee7d18 EFLAGS: 00010246
> Oct 9 08:06:43 hal kernel: [408578.629143] RAX: 0a00000000080068 RBX: ffffea001d1dbe70 RCX: ffff880c02d18978
> Oct 9 08:06:43 hal kernel: [408578.629143] RDX: 0000000000851a42 RSI: ffff880d8fe33618 RDI: ffffea002a09dd50
> Oct 9 08:06:43 hal kernel: [408578.629143] RBP: ffff88021cee7d38 R08: ffff880d8fe33618 R09: 0000000000000028
> Oct 9 08:06:43 hal kernel: [408578.629143] R10: ffff881006eb0f00 R11: f800000000851a42 R12: ffffea002a09dd40
> Oct 9 08:06:43 hal kernel: [408578.629143] R13: 0000000c02d18978 R14: 00000000d872f000 R15: ffff880d8fe33618
> Oct 9 08:06:43 hal kernel: [408578.629143] FS: 00007f864d7fa700(0000) GS:ffff880c1fc80000(0063) knlGS:00000000f432a910
> Oct 9 08:06:43 hal kernel: [408578.629143] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
> Oct 9 08:06:43 hal kernel: [408578.629143] CR2: 00000000d872f000 CR3: 000000100668c000 CR4: 00000000000006e0
> Oct 9 08:06:43 hal kernel: [408578.629143] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> Oct 9 08:06:43 hal kernel: [408578.629143] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Oct 9 08:06:43 hal kernel: [408578.629143] Process bitgen (pid: 29214, threadinfo ffff88021cee6000, task ffff880407b06900)
> Oct 9 08:06:43 hal kernel: [408578.629143] Stack:
> Oct 9 08:06:43 hal kernel: [408578.629143] 00000000dcef4000 ffff880c00968c98 ffff880c02d18978 000000010a34843e
> Oct 9 08:06:43 hal kernel: [408578.629143] ffff88021cee7de8 ffffffff811016a1 ffff88021cee7d78 ffff881006eb0f00
> Oct 9 08:06:43 hal kernel: [408578.629143] ffff88021cee7d98 ffffffff810feee2 ffff880c06f0d170 8000000b98d14067
> Oct 9 08:06:43 hal kernel: [408578.629143] Call Trace:
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff811016a1>] handle_pte_fault+0xae1/0xaf0
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff810feee2>] ? __pte_alloc+0x42/0x120
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff8112c26b>] ? do_huge_pmd_anonymous_page+0xab/0x310
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff81102a31>] handle_mm_fault+0x181/0x310
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff81106097>] ? vma_adjust+0x537/0x570
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff81424bed>] do_page_fault+0x11d/0x4e0
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff81109a05>] ? do_mremap+0x2d5/0x570
> Oct 9 08:06:43 hal kernel: [408578.629143] [<ffffffff81421d5f>] page_fault+0x1f/0x30
> Oct 9 08:06:43 hal kernel: [408578.629143] Code: 80 00 00 00 00 31 f6 48 89 df e8 e6 58 fb ff eb d7 85 c9 0f 84 44 ff ff ff 8d 51 01 89 c8 f0 0f b1 16 39 c1 90 74 b5 89 c1 eb e6 <0f> 0b 0f 1f 84 00 00 00 00 00 55 48 89 e5 48 83 ec 20 48 85 ff
> Oct 9 08:06:43 hal kernel: [408578.629143] RIP [<ffffffff81127b76>] migration_entry_wait+0x156/0x160
> Oct 9 08:06:43 hal kernel: [408578.629143] RSP <ffff88021cee7d18>
> Oct 9 08:06:43 hal kernel: [408578.642823] ---[ end trace 0a37362301163711 ]---
> Oct 9 08:07:10 hal kernel: [408605.283257] BUG: soft lockup - CPU#12 stuck for 23s! [par:29801]
> Oct 9 08:07:10 hal kernel: [408605.285807] CPU 12
> Oct 9 08:07:10 hal kernel: [408605.285807]
> Oct 9 08:07:10 hal kernel: [408605.285807] Pid: 29801, comm: par Tainted: G D 3.0.4 #5 Supermicro H8DGU/H8DGU
> Oct 9 08:07:10 hal kernel: [408605.285807] RIP: 0010:[<ffffffff814216a4>] [<ffffffff814216a4>] _raw_spin_lock+0x14/0x20
> Oct 9 08:07:10 hal kernel: [408605.285807] RSP: 0018:ffff880c02def808 EFLAGS: 00000293
> Oct 9 08:07:10 hal kernel: [408605.285807] RAX: 0000000000000b09 RBX: ffffea002741f6b8 RCX: ffff880000000000
> Oct 9 08:07:10 hal kernel: [408605.285807] RDX: ffffea0000000000 RSI: 000000002a09dd40 RDI: ffffea002a09dd50
> Oct 9 08:07:10 hal kernel: [408605.285807] RBP: ffff880c02def808 R08: 0000000000000000 R09: ffff880f2e4f4d70
> Oct 9 08:07:10 hal kernel: [408605.285807] R10: ffff880c1fffbe00 R11: 0000000000000050 R12: ffffffff8142988e
> Oct 9 08:07:10 hal kernel: [408605.285807] R13: ffff880c02def7b8 R14: ffffffff810e63dc R15: ffff880c02def7b8
> Oct 9 08:07:10 hal kernel: [408605.285807] FS: 00007fe6b677c720(0000) GS:ffff880c1fc00000(0063) knlGS:00000000f6e0d910
> Oct 9 08:07:10 hal kernel: [408605.285807] CS: 0010 DS: 002b ES: 002b CR0: 000000008005003b
> Oct 9 08:07:10 hal kernel: [408605.285807] CR2: 00000000dd40012c CR3: 00000009f6b78000 CR4: 00000000000006e0
> Oct 9 08:07:10 hal kernel: [408605.285807] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> Oct 9 08:07:10 hal kernel: [408605.285807] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Oct 9 08:07:10 hal kernel: [408605.285807] Process par (pid: 29801, threadinfo ffff880c02dee000, task ffff880c07c90700)
> Oct 9 08:07:10 hal kernel: [408605.285807] Stack:
> Oct 9 08:07:10 hal kernel: [408605.285807] ffff880c02def858 ffffffff8110a2d7 ffffea001fc16fe0 ffff880c02d183a8
> Oct 9 08:07:10 hal kernel: [408605.285807] ffff880c02def8c8 ffffea001fc16fa8 ffff880c00968c98 ffff881006eb0f00
> Oct 9 08:07:10 hal kernel: [408605.285807] 0000000000000301 00000000d8675000 ffff880c02def8c8 ffffffff8110aa6a
> Oct 9 08:07:10 hal kernel: [408605.285807] Call Trace:
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8110a2d7>] __page_check_address+0x107/0x1a0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8110aa6a>] try_to_unmap_one+0x3a/0x420
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8110be44>] try_to_unmap_anon+0xb4/0x130
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8110bf75>] try_to_unmap+0x65/0x80
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff811285d0>] migrate_pages+0x310/0x4c0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff810e93c2>] ? ____pagevec_lru_add+0x12/0x20
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8111cbf0>] ? ftrace_define_fields_mm_compaction_isolate_template+0x70/0x70
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8111d5da>] compact_zone+0x52a/0x8c0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff810f9919>] ? zone_statistics+0x99/0xc0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8111dade>] compact_zone_order+0x7e/0xb0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff810e46a8>] ? get_page_from_freelist+0x3b8/0x7e0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8111dbcd>] try_to_compact_pages+0xbd/0xf0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff810e5148>] __alloc_pages_direct_compact+0xa8/0x180
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff810e56c5>] __alloc_pages_nodemask+0x4a5/0x7f0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff810e9698>] ? lru_cache_add_lru+0x28/0x50
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8110a92d>] ? page_add_new_anon_rmap+0x9d/0xb0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8111b865>] alloc_pages_vma+0x95/0x180
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8112c2f8>] do_huge_pmd_anonymous_page+0x138/0x310
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff81102ace>] handle_mm_fault+0x21e/0x310
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff81001716>] ? __switch_to+0x1e6/0x2c0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff81424bed>] do_page_fault+0x11d/0x4e0
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8141f178>] ? schedule+0x308/0xa10
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff811077a7>] ? do_mmap_pgoff+0x357/0x370
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff8110790d>] ? sys_mmap_pgoff+0x14d/0x220
> Oct 9 08:07:10 hal kernel: [408605.285807] [<ffffffff81421d5f>] page_fault+0x1f/0x30
> Oct 9 08:07:10 hal kernel: [408605.285807] Code: 0f b6 c2 85 c0 0f 95 c0 0f b6 c0 5d c3 66 2e 0f 1f 84 00 00 00 00 00 55 b8 00 01 00 00 48 89 e5 f0 66 0f c1 07 38 e0 74 06 f3 90 <8a> 07 eb f6 5d c3 66 0f 1f 44 00 00 55 48 89 e5 9c 58 fa ba 00

I guess this is the only time you've seen this? In which case, ideally
I would try to devise a testcase to demonstrate the issue below instead;
but that may involve more ingenuity than I can find time for, let's see
see if people approve of this patch anyway (it applies to 3.1 or 3.0,
and earlier releases except that i_mmap_mutex used to be i_mmap_lock).


[PATCH] mm: add anon_vma locking to mremap move

I don't usually pay much attention to the stale "? " addresses in
stack backtraces, but this lucky report from Pawel Sikora hints that
mremap's move_ptes() has inadequate locking against page migration.

3.0 BUG_ON(!PageLocked(p)) in migration_entry_to_page():
kernel BUG at include/linux/swapops.h:105!
RIP: 0010:[<ffffffff81127b76>] [<ffffffff81127b76>]
migration_entry_wait+0x156/0x160
[<ffffffff811016a1>] handle_pte_fault+0xae1/0xaf0
[<ffffffff810feee2>] ? __pte_alloc+0x42/0x120
[<ffffffff8112c26b>] ? do_huge_pmd_anonymous_page+0xab/0x310
[<ffffffff81102a31>] handle_mm_fault+0x181/0x310
[<ffffffff81106097>] ? vma_adjust+0x537/0x570
[<ffffffff81424bed>] do_page_fault+0x11d/0x4e0
[<ffffffff81109a05>] ? do_mremap+0x2d5/0x570
[<ffffffff81421d5f>] page_fault+0x1f/0x30
mremap's down_write of mmap_sem, together with i_mmap_mutex/lock,
and pagetable locks, were good enough before page migration (with its
requirement that every migration entry be found) came in; and enough
while migration always held mmap_sem. But not enough nowadays, when
there's memory hotremove and compaction: anon_vma lock is also needed,
to make sure a migration entry is not dodging around behind our back.

It appears that Mel's a8bef8ff6ea1 "mm: migration: avoid race between
shift_arg_pages() and rmap_walk() during migration by not migrating
temporary stacks" was actually a workaround for this in the special
common case of exec's use of move_pagetables(); and we should probably
now remove that VM_STACK_INCOMPLETE_SETUP stuff as a separate cleanup.

Reported-by: Pawel Sikora <pluto@agmk.net>
Cc: stable@kernel.org
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/mremap.c | 5 +++++
1 file changed, 5 insertions(+)
--- 3.1-rc9/mm/mremap.c 2011-07-21 19:17:23.000000000 -0700
+++ linux/mm/mremap.c 2011-10-13 14:36:25.097780974 -0700
@@ -77,6 +77,7 @@ static void move_ptes(struct vm_area_str
unsigned long new_addr)
{
struct address_space *mapping = NULL;
+ struct anon_vma *anon_vma = vma->anon_vma;
struct mm_struct *mm = vma->vm_mm;
pte_t *old_pte, *new_pte, pte;
spinlock_t *old_ptl, *new_ptl;
@@ -95,6 +96,8 @@ static void move_ptes(struct vm_area_str
mapping = vma->vm_file->f_mapping;
mutex_lock(&mapping->i_mmap_mutex);
}
+ if (anon_vma)
+ anon_vma_lock(anon_vma);

/*
* We don't have to worry about the ordering of src and dst
@@ -121,6 +124,8 @@ static void move_ptes(struct vm_area_str
spin_unlock(new_ptl);
pte_unmap(new_pte - 1);
pte_unmap_unlock(old_pte - 1, old_ptl);
+ if (anon_vma)
+ anon_vma_unlock(anon_vma);
if (mapping)
mutex_unlock(&mapping->i_mmap_mutex);
mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);

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