Date:   Wed, 30 May 2018 10:53:58 -0700
From:   Qing Huang <qing.huang@...cle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     tariqt@...lanox.com, haakon.bugge@...cle.com,
        yanjun.zhu@...cle.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        gi-oh.kim@...fitbricks.com
Subject: Re: [PATCH V4] mlx4_core: allocate ICM memory in page size chunks



On 5/29/2018 8:34 PM, Eric Dumazet wrote:
>
> On 05/25/2018 10:23 AM, David Miller wrote:
>> From: Qing Huang <qing.huang@...cle.com>
>> Date: Wed, 23 May 2018 16:22:46 -0700
>>
>>> When a system is under memory presure (high usage with fragments),
>>> the original 256KB ICM chunk allocations will likely trigger kernel
>>> memory management to enter slow path doing memory compact/migration
>>> ops in order to complete high order memory allocations.
>>>
>>> When that happens, user processes calling uverb APIs may get stuck
>>> for more than 120s easily even though there are a lot of free pages
>>> in smaller chunks available in the system.
>>>
>>> Syslog:
>>> ...
>>> Dec 10 09:04:51 slcc03db02 kernel: [397078.572732] INFO: task
>>> oracle_205573_e:205573 blocked for more than 120 seconds.
>>> ...
>>>
>>> With 4KB ICM chunk size on x86_64 arch, the above issue is fixed.
>>>
>>> However in order to support smaller ICM chunk size, we need to fix
>>> another issue in large size kcalloc allocations.
>>>
>>> E.g.
>>> Setting log_num_mtt=30 requires 1G mtt entries. With the 4KB ICM chunk
>>> size, each ICM chunk can only hold 512 mtt entries (8 bytes for each mtt
>>> entry). So we need a 16MB allocation for a table->icm pointer array to
>>> hold 2M pointers which can easily cause kcalloc to fail.
>>>
>>> The solution is to use kvzalloc to replace kcalloc which will fall back
>>> to vmalloc automatically if kmalloc fails.
>>>
>>> Signed-off-by: Qing Huang <qing.huang@...cle.com>
>>> Acked-by: Daniel Jurgens <danielj@...lanox.com>
>>> Reviewed-by: Zhu Yanjun <yanjun.zhu@...cle.com>
>> Applied, thanks.
>>
> I must say this patch causes regressions here.
>
> KASAN is not happy.
>
> It looks that you guys did not really looked at mlx4_alloc_icm()
>
> This function is properly handling high order allocations with fallbacks to order-0 pages
> under high memory pressure.
>
> BUG: KASAN: slab-out-of-bounds in to_rdma_ah_attr+0x808/0x9e0 [mlx4_ib]
> Read of size 4 at addr ffff8817df584f68 by task qp_listing_test/92585
>
> CPU: 38 PID: 92585 Comm: qp_listing_test Tainted: G           O
> Call Trace:
>   [<ffffffffba80d7bb>] dump_stack+0x4d/0x72
>   [<ffffffffb951dc5f>] print_address_description+0x6f/0x260
>   [<ffffffffb951e1c7>] kasan_report+0x257/0x370
>   [<ffffffffb951e339>] __asan_report_load4_noabort+0x19/0x20
>   [<ffffffffc0256d28>] to_rdma_ah_attr+0x808/0x9e0 [mlx4_ib]
>   [<ffffffffc02785b3>] mlx4_ib_query_qp+0x1213/0x1660 [mlx4_ib]
>   [<ffffffffc02dbfdb>] qpstat_print_qp+0x13b/0x500 [ib_uverbs]
>   [<ffffffffc02dc3ea>] qpstat_seq_show+0x4a/0xb0 [ib_uverbs]
>   [<ffffffffb95f125c>] seq_read+0xa9c/0x1230
>   [<ffffffffb96e0821>] proc_reg_read+0xc1/0x180
>   [<ffffffffb9577918>] __vfs_read+0xe8/0x730
>   [<ffffffffb9578057>] vfs_read+0xf7/0x300
>   [<ffffffffb95794d2>] SyS_read+0xd2/0x1b0
>   [<ffffffffb8e06b16>] do_syscall_64+0x186/0x420
>   [<ffffffffbaa00071>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> RIP: 0033:0x7f851a7bb30d
> RSP: 002b:00007ffd09a758c0 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 00007f84ff959440 RCX: 00007f851a7bb30d
> RDX: 000000000003fc00 RSI: 00007f84ff60a000 RDI: 000000000000000b
> RBP: 00007ffd09a75900 R08: 00000000ffffffff R09: 0000000000000000
> R10: 0000000000000022 R11: 0000000000000293 R12: 0000000000000000
> R13: 000000000003ffff R14: 000000000003ffff R15: 00007f84ff60a000
>
> Allocated by task 4488:
>   save_stack+0x46/0xd0
>   kasan_kmalloc+0xad/0xe0
>   __kmalloc+0x101/0x5e0
>   ib_register_device+0xc03/0x1250 [ib_core]
>   mlx4_ib_add+0x27d6/0x4dd0 [mlx4_ib]
>   mlx4_add_device+0xa9/0x340 [mlx4_core]
>   mlx4_register_interface+0x16e/0x390 [mlx4_core]
>   xhci_pci_remove+0x7a/0x180 [xhci_pci]
>   do_one_initcall+0xa0/0x230
>   do_init_module+0x1b9/0x5a4
>   load_module+0x63e6/0x94c0
>   SYSC_init_module+0x1a4/0x1c0
>   SyS_init_module+0xe/0x10
>   do_syscall_64+0x186/0x420
>   entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>
> Freed by task 0:
> (stack is not available)
>
> The buggy address belongs to the object at ffff8817df584f40
>   which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 8 bytes to the right of
>   32-byte region [ffff8817df584f40, ffff8817df584f60)
> The buggy address belongs to the page:
> page:ffffea005f7d6100 count:1 mapcount:0 mapping:ffff8817df584000 index:0xffff8817df584fc1
> flags: 0x880000000000100(slab)
> raw: 0880000000000100 ffff8817df584000 ffff8817df584fc1 000000010000003f
> raw: ffffea005f3ac0a0 ffffea005c476760 ffff8817fec00900 ffff883ff78d26c0
> page dumped because: kasan: bad access detected
> page->mem_cgroup:ffff883ff78d26c0

What kind of test case did you run? It looks like a bug somewhere in the 
code.
Perhaps smaller chunks make it easier to occur, we should fix the bug 
though.


>
> Memory state around the buggy address:
>   ffff8817df584e00: 00 03 fc fc fc fc fc fc 00 03 fc fc fc fc fc fc
>   ffff8817df584e80: 00 00 00 04 fc fc fc fc 00 00 00 fc fc fc fc fc
>> ffff8817df584f00: fb fb fb fb fc fc fc fc 00 00 00 00 fc fc fc fc
>                                                            ^
>   ffff8817df584f80: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff8817df585000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>
> I will test :
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/icm.c b/drivers/net/ethernet/mellanox/mlx4/icm.c
> index 685337d58276fc91baeeb64387c52985e1bc6dda..4d2a71381acb739585d662175e86caef72338097 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/icm.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/icm.c
> @@ -43,12 +43,13 @@
>   #include "fw.h"
>   
>   /*
> - * We allocate in page size (default 4KB on many archs) chunks to avoid high
> - * order memory allocations in fragmented/high usage memory situation.
> + * We allocate in as big chunks as we can, up to a maximum of 256 KB
> + * per chunk. Note that the chunks are not necessarily in contiguous
> + * physical memory.
>    */
>   enum {
> -       MLX4_ICM_ALLOC_SIZE     = PAGE_SIZE,
> -       MLX4_TABLE_CHUNK_SIZE   = PAGE_SIZE,
> +       MLX4_ICM_ALLOC_SIZE     = 1 << 18,
> +       MLX4_TABLE_CHUNK_SIZE   = 1 << 18
>   };
>   
>   static void mlx4_free_icm_pages(struct mlx4_dev *dev, struct mlx4_icm_chunk *chunk)
> --
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