Re: [PATCH akpm] mm: include VM_MIXEDMAP flag in the VM_SPECIAL list to avoid m(un)locking

[Hannes Frederic Sowa]

On Sun, Feb 16, 2014 at 03:59:45PM +0100, Daniel Borkmann wrote:
> From: Vlastimil Babka <vbabka@xxxxxxx>
> 
> [ 4366.519657] ------------[ cut here ]------------
> [ 4366.519709] kernel BUG at mm/mlock.c:528!
> [ 4366.519742] invalid opcode: 0000 [#1] SMP
> [ 4366.519782] Modules linked in: ccm arc4 iwldvm [...]
> [ 4366.520488]  video
> [ 4366.520501] CPU: 3 PID: 2266 Comm: netsniff-ng Not tainted 3.14.0-rc2+ #8
> [ 4366.520551] Hardware name: LENOVO 2429BP3/2429BP3, BIOS G4ET37WW (1.12 ) 05/29/2012
> [ 4366.520608] task: ffff8801f87f9820 ti: ffff88002cb44000 task.ti: ffff88002cb44000
> [ 4366.520662] RIP: 0010:[<ffffffff81171ad0>]  [<ffffffff81171ad0>] munlock_vma_pages_range+0x2e0/0x2f0
> [ 4366.520738] RSP: 0018:ffff88002cb45e00  EFLAGS: 00010206
> [ 4366.520777] RAX: 00000000000001ff RBX: ffff8801f5e75d10 RCX: 000000000000107d
> [ 4366.520829] RDX: 00000007f133345f RSI: ffffea0007d76000 RDI: ffffea0007d76000
> [ 4366.520881] RBP: ffff88002cb45ed8 R08: 0000000000000000 R09: a8001f5d80000000
> [ 4366.520932] R10: 57ffcaa287d76000 R11: 0000000000000246 R12: ffffea0007d76000
> [ 4366.520983] R13: 00007f133745f000 R14: 00007f133345f000 R15: ffff8801f5e75a50
> [ 4366.521036] FS:  00007f133745f740(0000) GS:ffff88021e2c0000(0000) knlGS:0000000000000000
> [ 4366.521094] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 4366.521137] CR2: 000000000062ead0 CR3: 00000000c688d000 CR4: 00000000001407e0
> [ 4366.521188] Stack:
> [ 4366.521205]  ffffffff8116b085 00007f133745efff 00007f133327d000 00007f133745f000
> [ 4366.521269]  000001ff81172793 ffff8800c6baa6e0 0000000000000000 0000000000000000
> [ 4366.521333]  00007f1333336000 ffffea0004a7ab40 ffff88002cb45e58 0000000000000000
> [ 4366.521397] Call Trace:
> [ 4366.521422]  [<ffffffff8116b085>] ? tlb_finish_mmu+0x35/0x60
> [ 4366.521468]  [<ffffffff8117486f>] do_munmap+0x18f/0x3b0
> [ 4366.521511]  [<ffffffff8163e84b>] ? packet_getsockopt+0xfb/0x310
> [ 4366.521558]  [<ffffffff81174ad1>] vm_munmap+0x41/0x60
> [ 4366.521598]  [<ffffffff811759b2>] SyS_munmap+0x22/0x30
> [ 4366.521639]  [<ffffffff81666616>] system_call_fastpath+0x1a/0x1f
> [ 4366.521683] Code: ff ff e8 c4 07 fe ff 84 c0 48 8b 95 28 ff ff ff 0f 85 52 ff ff
>                      ff e9 3e ff ff ff 48 89 d7 e8 bf 32 4e 00 4c 89 e7 e8 aa 32 4e
>                      00 <0f> 0b 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44
>                      00 00
> [ 4366.522004] RIP  [<ffffffff81171ad0>] munlock_vma_pages_range+0x2e0/0x2f0
> [ 4366.522059]  RSP <ffff88002cb45e00>
> [ 4366.539269] ---[ end trace a0088dcf07ae10f2 ]---
> 
> Daniel Borkmann reported a bug (stack trace above) with VM_BUG_ON
> assertions failing where munlock_vma_pages_range() thinks it's
> unexpectedly in the middle of a THP page. This can be reproduced
> with default config since 3.11 kernels. A reproducer can be found
> in the kernel's selftest directory for networking by running
> ./psock_tpacket.
> 
> The problem is that an order=2 compound page (allocated by
> alloc_one_pg_vec_page() is part of the munlocked VM_MIXEDMAP
> vma (mapped by packet_mmap()) and mistaken for a THP page and
> assumed to be order=9.
> 
> The checks for THP in munlock came with commit ff6a6da60b89 ("mm:
> accelerate munlock() treatment of THP pages"), i.e. since 3.9,
> but did not trigger a bug. It just makes munlock_vma_pages_range()
> skip such compound pages until the next 512-pages-aligned page,
> when it encounters a head page. This is however not a problem
> for vma's where mlocking has no effect anyway, but it can distort
> the accounting.
> 
> Since commit 7225522bb ("mm: munlock: batch non-THP page isolation
> and munlock+putback using pagevec") this can trigger a VM_BUG_ON
> in PageTransHuge() check.
> 
> This patch fixes the issue by adding VM_MIXEDMAP flag to VM_SPECIAL,
> a list of flags that make vma's non-mlockable and non-mergeable.
> The reasoning is that VM_MIXEDMAP vma's are similar to VM_PFNMAP,
> which is already on the VM_SPECIAL list, and both are intended
> for non-LRU pages where mlocking makes no sense anyway. Related
> Lkml discussion can be found in [2].
> 
>  [1] tools/testing/selftests/net/psock_tpacket
>  [2] https://lkml.org/lkml/2014/1/10/427
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Reported-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> Tested-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> Cc: John David Anglin <dave.anglin@xxxxxxxx>
> Cc: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
> Cc: Carsten Otte <cotte@xxxxxxxxxx>
> Cc: Jared Hulbert <jaredeh@xxxxxxxxx>
> Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> [3.11.x+]

Tested-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>

Thanks Daniel!

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