一例智能网卡 (mellanox) 的网卡故障分析
发布于: 2 小时前
背景：这个是在 centos 7.6.1810 的环境上复现的，智能网卡是目前很多云服务器上的网卡标配，在 OPPO 主要用于 vpc 等场景，智能网卡的代码随着功能的增强导致复杂度一直在上升，驱动的 bug 一直是内核 bug 中的大头，在遇到类似问题时，内核开发者由于对驱动代码不熟悉，排查会比较费劲,本身涉及的背景知识有：dma_pool,dma_page,net_device,mlx5_core_dev 设备，设备卸载，uaf 问题等,另外，这个 bug 目测在最新的 linux 基线也没有解决,本文单独拿出来列举是因为 uaf 问题相对比较独特。下面列一下我们是怎么排查并解决这个问题的。
一、故障现象
OPPO 云内核团队接到连通性告警报障，发现机器复位：
UPTIME: 00:04:16-------------运行的时间很短LOAD AVERAGE: 0.25, 0.23, 0.11TASKS: 2027RELEASE: 3.10.0-1062.18.1.el7.x86_64MEMORY: 127.6 GBPANIC: "BUG: unable to handle kernel NULL pointer dereference at (null)"PID: 23283COMMAND: "spider-agent"TASK: ffff9d1fbb090000 [THREAD_INFO: ffff9d1f9a0d8000]CPU: 0STATE: TASK_RUNNING (PANIC)
crash> btPID: 23283 TASK: ffff9d1fbb090000 CPU: 0 COMMAND: "spider-agent" #0 [ffff9d1f9a0db650] machine_kexec at ffffffffb6665b34 #1 [ffff9d1f9a0db6b0] __crash_kexec at ffffffffb6722592 #2 [ffff9d1f9a0db780] crash_kexec at ffffffffb6722680 #3 [ffff9d1f9a0db798] oops_end at ffffffffb6d85798 #4 [ffff9d1f9a0db7c0] no_context at ffffffffb6675bb4 #5 [ffff9d1f9a0db810] __bad_area_nosemaphore at ffffffffb6675e82 #6 [ffff9d1f9a0db860] bad_area_nosemaphore at ffffffffb6675fa4 #7 [ffff9d1f9a0db870] __do_page_fault at ffffffffb6d88750 #8 [ffff9d1f9a0db8e0] do_page_fault at ffffffffb6d88975 #9 [ffff9d1f9a0db910] page_fault at ffffffffb6d84778 [exception RIP: dma_pool_alloc+427]//caq:异常地址 RIP: ffffffffb680efab RSP: ffff9d1f9a0db9c8 RFLAGS: 00010046 RAX: 0000000000000246 RBX: ffff9d0fa45f4c80 RCX: 0000000000001000 RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffff9d0fa45f4c10 RBP: ffff9d1f9a0dba20 R8: 000000000001f080 R9: ffff9d00ffc07c00 R10: ffffffffc03e10c4 R11: ffffffffb67dd6fd R12: 00000000000080d0 R13: ffff9d0fa45f4c10 R14: ffff9d0fa45f4c00 R15: 0000000000000000 ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018#10 [ffff9d1f9a0dba28] mlx5_alloc_cmd_msg at ffffffffc03e10e3 [mlx5_core]//涉及的模块#11 [ffff9d1f9a0dba78] cmd_exec at ffffffffc03e3c92 [mlx5_core]#12 [ffff9d1f9a0dbb18] mlx5_cmd_exec at ffffffffc03e442b [mlx5_core]#13 [ffff9d1f9a0dbb48] mlx5_core_access_reg at ffffffffc03ee354 [mlx5_core]#14 [ffff9d1f9a0dbba0] mlx5_query_port_ptys at ffffffffc03ee411 [mlx5_core]#15 [ffff9d1f9a0dbc10] mlx5e_get_link_ksettings at ffffffffc0413035 [mlx5_core]#16 [ffff9d1f9a0dbce8] __ethtool_get_link_ksettings at ffffffffb6c56d06#17 [ffff9d1f9a0dbd48] speed_show at ffffffffb6c705b8#18 [ffff9d1f9a0dbdd8] dev_attr_show at ffffffffb6ab1643#19 [ffff9d1f9a0dbdf8] sysfs_kf_seq_show at ffffffffb68d709f#20 [ffff9d1f9a0dbe18] kernfs_seq_show at ffffffffb68d57d6#21 [ffff9d1f9a0dbe28] seq_read at ffffffffb6872a30#22 [ffff9d1f9a0dbe98] kernfs_fop_read at ffffffffb68d6125#23 [ffff9d1f9a0dbed8] vfs_read at ffffffffb684a8ff#24 [ffff9d1f9a0dbf08] sys_read at ffffffffb684b7bf#25 [ffff9d1f9a0dbf50] system_call_fastpath at ffffffffb6d8dede RIP: 00000000004a5030 RSP: 000000c001099378 RFLAGS: 00000212 RAX: 0000000000000000 RBX: 000000c000040000 RCX: ffffffffffffffff RDX: 000000000000000a RSI: 000000c00109976e RDI: 000000000000000d---read的文件fd编号 RBP: 000000c001099640 R8: 0000000000000000 R9: 0000000000000000 R10: 0000000000000000 R11: 0000000000000206 R12: 000000000000000c R13: 0000000000000032 R14: 0000000000f710c4 R15: 0000000000000000 ORIG_RAX: 0000000000000000 CS: 0033 SS: 002b
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从堆栈看，是某进程读取文件触发了一个内核态的空指针引用。
二、故障现象分析
从堆栈信息看：
1、当时进程打开 fd 编号为 13 的文件，这个从 rdi 的值可以看出。
2、speed_show 和 __ethtool_get_link_ksettings 表示在读取网卡的速率值下面看下打开的文件是哪个，
crash> files 23283PID: 23283 TASK: ffff9d1fbb090000 CPU: 0 COMMAND: "spider-agent"ROOT: /rootfs CWD: /rootfs/home/service/app/spider FD FILE DENTRY INODE TYPE PATH.... 9 ffff9d0f5709b200 ffff9d1facc80a80 ffff9d1069a194d0 REG /rootfs/sys/devices/pci0000:3a/0000:3a:00.0/0000:3b:00.0/net/p1p1/speed---这个还在 10 ffff9d0f4a45a400 ffff9d0f9982e240 ffff9d0fb7b873a0 REG /rootfs/sys/devices/pci0000:5d/0000:5d:00.0/0000:5e:00.0/net/p3p1/speed---注意对应关系 0000:5e:00.0 对应p3p1 11 ffff9d0f57098f00 ffff9d1facc80240 ffff9d1069a1b530 REG /rootfs/sys/devices/pci0000:3a/0000:3a:00.0/0000:3b:00.1/net/p1p2/speed---这个还在 13 ffff9d0f4a458a00 ffff9d0f9982e0c0 ffff9d0fb7b875f0 REG /rootfs/sys/devices/pci0000:5d/0000:5d:00.0/0000:5e:00.1/net/p3p2/speed---注意对应关系 0000:5e:00.1 对应p3p2....
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注意上面 pci 编号与 网卡名称的对应关系，后面会用到。打开文件读取 speed 本身应该是一个很常见的流程，下面从 exception RIP: dma_pool_alloc+427 进一步分析为什么触发了 NULL pointer dereference 展开具体的堆栈如下：
#9 [ffff9d1f9a0db910] page_fault at ffffffffb6d84778 [exception RIP: dma_pool_alloc+427] RIP: ffffffffb680efab RSP: ffff9d1f9a0db9c8 RFLAGS: 00010046 RAX: 0000000000000246 RBX: ffff9d0fa45f4c80 RCX: 0000000000001000 RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffff9d0fa45f4c10 RBP: ffff9d1f9a0dba20 R8: 000000000001f080 R9: ffff9d00ffc07c00 R10: ffffffffc03e10c4 R11: ffffffffb67dd6fd R12: 00000000000080d0 R13: ffff9d0fa45f4c10 R14: ffff9d0fa45f4c00 R15: 0000000000000000 ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 ffff9d1f9a0db918: 0000000000000000 ffff9d0fa45f4c00 ffff9d1f9a0db928: ffff9d0fa45f4c10 00000000000080d0 ffff9d1f9a0db938: ffff9d1f9a0dba20 ffff9d0fa45f4c80 ffff9d1f9a0db948: ffffffffb67dd6fd ffffffffc03e10c4 ffff9d1f9a0db958: ffff9d00ffc07c00 000000000001f080 ffff9d1f9a0db968: 0000000000000246 0000000000001000 ffff9d1f9a0db978: 0000000000000000 0000000000000246 ffff9d1f9a0db988: ffff9d0fa45f4c10 ffffffffffffffff ffff9d1f9a0db998: ffffffffb680efab 0000000000000010 ffff9d1f9a0db9a8: 0000000000010046 ffff9d1f9a0db9c8 ffff9d1f9a0db9b8: 0000000000000018 ffffffffb680ee45 ffff9d1f9a0db9c8: ffff9d0faf9fec40 0000000000000000 ffff9d1f9a0db9d8: ffff9d0faf9fec48 ffffffffb682669c ffff9d1f9a0db9e8: ffff9d00ffc07c00 00000000618746c1 ffff9d1f9a0db9f8: 0000000000000000 0000000000000000 ffff9d1f9a0dba08: ffff9d0faf9fec40 0000000000000000 ffff9d1f9a0dba18: ffff9d0fa3c800c0 ffff9d1f9a0dba70 ffff9d1f9a0dba28: ffffffffc03e10e3 #10 [ffff9d1f9a0dba28] mlx5_alloc_cmd_msg at ffffffffc03e10e3 [mlx5_core] ffff9d1f9a0dba30: ffff9d0f4eebee00 0000000000000001 ffff9d1f9a0dba40: 000000d0000080d0 0000000000000050 ffff9d1f9a0dba50: ffff9d0fa3c800c0 0000000000000005 --r12是rdi ,ffff9d0fa3c800c0 ffff9d1f9a0dba60: ffff9d0fa3c803e0 ffff9d1f9d87ccc0 ffff9d1f9a0dba70: ffff9d1f9a0dbb10 ffffffffc03e3c92 #11 [ffff9d1f9a0dba78] cmd_exec at ffffffffc03e3c92 [mlx5_core]
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从堆栈中取出对应的 mlx5_core_dev 为 ffff9d0fa3c800c0
crash> mlx5_core_dev.cmd ffff9d0fa3c800c0 -xostruct mlx5_core_dev { [ffff9d0fa3c80138] struct mlx5_cmd cmd;}crash> mlx5_cmd.pool ffff9d0fa3c80138 pool = 0xffff9d0fa45f4c00------这个就是dma_pool，写驱动代码的同学会经常遇到
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出问题的代码行号为：
crash> dis -l dma_pool_alloc+427 -B 5/usr/src/debug/kernel-3.10.0-1062.18.1.el7/linux-3.10.0-1062.18.1.el7.x86_64/mm/dmapool.c: 3340xffffffffb680efab <dma_pool_alloc+427>: mov (%r15),%ecx而对应的r15，从上面的堆栈看，确实是null。 305 void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags, 306 dma_addr_t *handle) 307 {... 315 spin_lock_irqsave(&pool->lock, flags); 316 list_for_each_entry(page, &pool->page_list, page_list) { 317 if (page->offset < pool->allocation)---//caq:当前满足条件 318 goto ready;//caq:跳转到ready 319 } 320 321 /* pool_alloc_page() might sleep, so temporarily drop &pool->lock */ 322 spin_unlock_irqrestore(&pool->lock, flags); 323 324 page = pool_alloc_page(pool, mem_flags & (~__GFP_ZERO)); 325 if (!page) 326 return NULL; 327 328 spin_lock_irqsave(&pool->lock, flags); 329 330 list_add(&page->page_list, &pool->page_list); 331 ready: 332 page->in_use++;//caq:表示正在引用 333 offset = page->offset;//从上次用完的地方开始使用 334 page->offset = *(int *)(page->vaddr + offset);//caq:出问题的行号... }
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从上面的代码看，page->vaddr 为 NULL,offset 也为 0，才会引用 NULL，page 有两个来源，
第一种是从 pool 中的 page_list 中取，
第二种是从 pool_alloc_page 临时申请，当然申请之后会挂入到 pool 中的 page_list,
下面查看一下这个 page_list.
crash> dma_pool ffff9d0fa45f4c00 -xstruct dma_pool { page_list = { next = 0xffff9d0fa45f4c80, prev = 0xffff9d0fa45f4c00 }, lock = { { rlock = { raw_lock = { val = { counter = 0x1 } } } } }, size = 0x400, dev = 0xffff9d1fbddec098, allocation = 0x1000, boundary = 0x1000, name = "mlx5_cmd\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", pools = { next = 0xdead000000000100, prev = 0xdead000000000200 }}
crash> list dma_pool.page_list -H 0xffff9d0fa45f4c00 -s dma_page.offset,vaddrffff9d0fa45f4c80 offset = 0 vaddr = 0x0ffff9d0fa45f4d00 offset = 0 vaddr = 0x0
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从 dma_pool_alloc 函数的代码逻辑看，pool->page_list 确实不为空，而且满足 if (page->offset < pool->allocation) 的条件，所以第一个 page 应该是 ffff9d0fa45f4c80 也就是从第一种情况取出的：
crash> dma_page ffff9d0fa45f4c80struct dma_page { page_list = { next = 0xffff9d0fa45f4d00, prev = 0xffff9d0fa45f4c80 }, vaddr = 0x0, //caq:这个异常，引用这个将导致crash dma = 0, in_use = 1, //caq:这个标记为在使用，符合page->in_use++; offset = 0}
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问题分析到这里，因为 dma_pool 中的 page，申请之后，vaddr 都会初始化，一般在 pool_alloc_page 中进行初始化，怎么可能会 NULL 呢？然后查看一下这个地址：
crash> kmem ffff9d0fa45f4c80-------这个是dma_pool中的pageCACHE NAME OBJSIZE ALLOCATED TOTAL SLABS SSIZEffff9d00ffc07900 kmalloc-128//caq:注意这个长度 128 8963 14976 234 8k SLAB MEMORY NODE TOTAL ALLOCATED FREE ffffe299c0917d00 ffff9d0fa45f4000 0 64 29 35 FREE / [ALLOCATED] ffff9d0fa45f4c80
PAGE PHYSICAL MAPPING INDEX CNT FLAGSffffe299c0917d00 10245f4000 0 ffff9d0fa45f4c00 1 2fffff00004080 slab,head
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由于以前用过类似的 dma 函数，印象中 dma_page 没有这么大，再看看第二个 dma_page 如下：
crash> kmem ffff9d0fa45f4d00CACHE NAME OBJSIZE ALLOCATED TOTAL SLABS SSIZEffff9d00ffc07900 kmalloc-128 128 8963 14976 234 8k SLAB MEMORY NODE TOTAL ALLOCATED FREE ffffe299c0917d00 ffff9d0fa45f4000 0 64 29 35 FREE / [ALLOCATED] ffff9d0fa45f4d00
PAGE PHYSICAL MAPPING INDEX CNT FLAGSffffe299c0917d00 10245f4000 0 ffff9d0fa45f4c00 1 2fffff00004080 slab,head
crash> dma_page ffff9d0fa45f4d00struct dma_page { page_list = { next = 0xffff9d0fa45f5000, prev = 0xffff9d0fa45f4d00 }, vaddr = 0x0, -----------caq：也是null dma = 0, in_use = 0, offset = 0}
crash> list dma_pool.page_list -H 0xffff9d0fa45f4c00 -s dma_page.offset,vaddrffff9d0fa45f4c80 offset = 0 vaddr = 0x0ffff9d0fa45f4d00 offset = 0 vaddr = 0x0ffff9d0fa45f5000 offset = 0 vaddr = 0x0.........
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看来不仅是第一个 dma_page 有问题，所有在 pool 中的 dma_page 单元都一样，那直接查看一下 dma_page 的正常大小：
crash> p sizeof(struct dma_page)$3 = 40
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按道理长度才 40 字节，就算申请 slab 的话，也应该扩展为 64 字节才对，怎么可能像上面那个 dma_page 一样是 128 字节呢？为了解开这个疑惑，找一个正常的其他节点对比一下：
crash> net NET_DEVICE NAME IP ADDRESS(ES)ffff8f9e800be000 lo 127.0.0.1ffff8f9e62640000 p1p1 ffff8f9e626c0000 p1p2 ffff8f9e627c0000 p3p1 -----//caq:以这个为例ffff8f9e62100000 p3p2
然后根据代码：通过net_device查看mlx5e_priv：
static int mlx5e_get_link_ksettings(struct net_device *netdev, struct ethtool_link_ksettings *link_ksettings){... struct mlx5e_priv *priv = netdev_priv(netdev);...}
static inline void *netdev_priv(const struct net_device *dev){ return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);}
crash> px sizeof(struct net_device)$2 = 0x8c0
crash> mlx5e_priv.mdev ffff8f9e627c08c0---根据偏移计算 mdev = 0xffff8f9e67c400c0
crash> mlx5_core_dev.cmd 0xffff8f9e67c400c0 -xostruct mlx5_core_dev { [ffff8f9e67c40138] struct mlx5_cmd cmd;}
crash> mlx5_cmd.pool ffff8f9e67c40138 pool = 0xffff8f9e7bf48f80
crash> dma_pool 0xffff8f9e7bf48f80struct dma_pool { page_list = { next = 0xffff8f9e79c60880, //caq:其中的一个dma_page prev = 0xffff8fae6e4db800 }, ....... size = 1024, dev = 0xffff8f9e800b3098, allocation = 4096, boundary = 4096, name = "mlx5_cmd\000\217\364{\236\217\377\377\300\217\364{\236\217\377\377\200\234>\250\217\217\377\377", pools = { next = 0xffff8f9e800b3290, prev = 0xffff8f9e800b3290 }}crash> dma_page 0xffff8f9e79c60880 //caq:查看这个dma_pagestruct dma_page { page_list = { next = 0xffff8f9e79c60840, -------其中的一个dma_page prev = 0xffff8f9e7bf48f80 }, vaddr = 0xffff8f9e6fc9b000, //caq:正常vaddr不可能会NULL的 dma = 69521223680, in_use = 0, offset = 0}
crash> kmem 0xffff8f9e79c60880CACHE NAME OBJSIZE ALLOCATED TOTAL SLABS SSIZEffff8f8fbfc07b00 kmalloc-64--正常长度 64 667921 745024 11641 4k SLAB MEMORY NODE TOTAL ALLOCATED FREE ffffde5140e71800 ffff8f9e79c60000 0 64 64 0 FREE / [ALLOCATED] [ffff8f9e79c60880]
PAGE PHYSICAL MAPPING INDEX CNT FLAGSffffde5140e71800 1039c60000 0 0 1 2fffff00000080 slab
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以上操作要求对 net_device 和 mlx5 相关驱动代码比较熟悉。相比于异常的 dma_page,正常的 dma_page 是一个 64 字节的 slab，所以很明显，要么这个是一个踩内存问题，要么是一个 uaf(used after free )问题。一般问题查到这，怎么快速判断是哪一种类型呢？因为这两种问题，涉及到内存紊乱，一般都比较难查，这时候需要跳出来，我们先看一下其他运行进程的情况，找到了一个进程如下：
crash> bt 48263PID: 48263 TASK: ffff9d0f4ee0a0e0 CPU: 56 COMMAND: "reboot" #0 [ffff9d0f95d7f958] __schedule at ffffffffb6d80d4a #1 [ffff9d0f95d7f9e8] schedule at ffffffffb6d811f9 #2 [ffff9d0f95d7f9f8] schedule_timeout at ffffffffb6d7ec48 #3 [ffff9d0f95d7faa8] wait_for_completion_timeout at ffffffffb6d81ae5 #4 [ffff9d0f95d7fb08] cmd_exec at ffffffffc03e41c9 [mlx5_core] #5 [ffff9d0f95d7fba8] mlx5_cmd_exec at ffffffffc03e442b [mlx5_core] #6 [ffff9d0f95d7fbd8] mlx5_core_destroy_mkey at ffffffffc03f085d [mlx5_core] #7 [ffff9d0f95d7fc40] mlx5_mr_cache_cleanup at ffffffffc0c60aab [mlx5_ib] #8 [ffff9d0f95d7fca8] mlx5_ib_stage_pre_ib_reg_umr_cleanup at ffffffffc0c45d32 [mlx5_ib] #9 [ffff9d0f95d7fcc0] __mlx5_ib_remove at ffffffffc0c4f450 [mlx5_ib]#10 [ffff9d0f95d7fce8] mlx5_ib_remove at ffffffffc0c4f4aa [mlx5_ib]#11 [ffff9d0f95d7fd00] mlx5_detach_device at ffffffffc03fe231 [mlx5_core]#12 [ffff9d0f95d7fd30] mlx5_unload_one at ffffffffc03dee90 [mlx5_core]#13 [ffff9d0f95d7fd60] shutdown at ffffffffc03def80 [mlx5_core]#14 [ffff9d0f95d7fd80] pci_device_shutdown at ffffffffb69d1cda#15 [ffff9d0f95d7fda8] device_shutdown at ffffffffb6ab3beb#16 [ffff9d0f95d7fdd8] kernel_restart_prepare at ffffffffb66b7916#17 [ffff9d0f95d7fde8] kernel_restart at ffffffffb66b7932#18 [ffff9d0f95d7fe00] SYSC_reboot at ffffffffb66b7ba9#19 [ffff9d0f95d7ff40] sys_reboot at ffffffffb66b7c4e#20 [ffff9d0f95d7ff50] system_call_fastpath at ffffffffb6d8dede RIP: 00007fc9be7a5226 RSP: 00007ffd9a19e448 RFLAGS: 00010246 RAX: 00000000000000a9 RBX: 0000000000000004 RCX: 0000000000000000 RDX: 0000000001234567 RSI: 0000000028121969 RDI: fffffffffee1dead RBP: 0000000000000002 R8: 00005575d529558c R9: 0000000000000000 R10: 00007fc9bea767b8 R11: 0000000000000206 R12: 0000000000000000 R13: 00007ffd9a19e690 R14: 0000000000000000 R15: 0000000000000000 ORIG_RAX: 00000000000000a9 CS: 0033 SS: 002b
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为什么会关注这个进程，因为这么多年以来，因为卸载模块引发的 uaf 问题排查不低于 20 次了，有时候是 reboot，有时候是 unload，有时候是在 work 中释放资源，所以直觉上，觉得和这个卸载有很大关系。下面分析一下，reboot 流程里面操作到哪了。
2141 void device_shutdown(void) 2142 { 2143 struct device *dev, *parent; 2144 2145 spin_lock(&devices_kset->list_lock); 2146 /* 2147 * Walk the devices list backward, shutting down each in turn. 2148 * Beware that device unplug events may also start pulling 2149 * devices offline, even as the system is shutting down. 2150 */ 2151 while (!list_empty(&devices_kset->list)) { 2152 dev = list_entry(devices_kset->list.prev, struct device, 2153 kobj.entry);........ 2178 if (dev->device_rh && dev->device_rh->class_shutdown_pre) { 2179 if (initcall_debug) 2180 dev_info(dev, "shutdown_pre\n"); 2181 dev->device_rh->class_shutdown_pre(dev); 2182 } 2183 if (dev->bus && dev->bus->shutdown) { 2184 if (initcall_debug) 2185 dev_info(dev, "shutdown\n"); 2186 dev->bus->shutdown(dev); 2187 } else if (dev->driver && dev->driver->shutdown) { 2188 if (initcall_debug) 2189 dev_info(dev, "shutdown\n"); 2190 dev->driver->shutdown(dev); 2191 } }
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从上面代码看出以下两点：
1、每个 device 的 kobj.entry 成员串接在 devices_kset->list 中。
2、每个设备的 shutdown 流程从 device_shutdown 看是串行的。
从 reboot 的堆栈看，卸载一个 mlx 设备的流程包含如下：
pci_device_shutdown-->shutdown-->mlx5_unload_one-->mlx5_detach_device-->mlx5_cmd_cleanup-->dma_pool_destroy
mlx5_detach_device 的流程分支为：
void dma_pool_destroy(struct dma_pool *pool){....... while (!list_empty(&pool->page_list)) {//caq:将pool中的dma_page一一删除 struct dma_page *page; page = list_entry(pool->page_list.next, struct dma_page, page_list); if (is_page_busy(page)) {....... list_del(&page->page_list); kfree(page); } else pool_free_page(pool, page);//每个dma_page去释放 }
kfree(pool);//caq：释放pool....... }
static void pool_free_page(struct dma_pool *pool, struct dma_page *page){ dma_addr_t dma = page->dma;
#ifdef DMAPOOL_DEBUG memset(page->vaddr, POOL_POISON_FREED, pool->allocation);#endif dma_free_coherent(pool->dev, pool->allocation, page->vaddr, dma); list_del(&page->page_list);//caq:释放后会将page_list成员毒化 kfree(page);}
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从 reboot 的堆栈中，查看对应的 信息
#4 [ffff9d0f95d7fb08] cmd_exec at ffffffffc03e41c9 [mlx5_core] ffff9d0f95d7fb10: ffffffffb735b580 ffff9d0f904caf18 ffff9d0f95d7fb20: ffff9d00ff801da8 ffff9d0f23121200 ffff9d0f95d7fb30: ffff9d0f23121740 ffff9d0fa7480138 ffff9d0f95d7fb40: 0000000000000000 0000001002020000 ffff9d0f95d7fb50: 0000000000000000 ffff9d0f95d7fbe8 ffff9d0f95d7fb60: ffff9d0f00000000 0000000000000000 ffff9d0f95d7fb70: 00000000756415e3 ffff9d0fa74800c0 ----mlx5_core_dev设备，对应的是 p3p1， ffff9d0f95d7fb80: ffff9d0f95d7fbf8 ffff9d0f95d7fbe8 ffff9d0f95d7fb90: 0000000000000246 ffff9d0f8f3a20b8 ffff9d0f95d7fba0: ffff9d0f95d7fbd0 ffffffffc03e442b #5 [ffff9d0f95d7fba8] mlx5_cmd_exec at ffffffffc03e442b [mlx5_core] ffff9d0f95d7fbb0: 0000000000000000 ffff9d0fa74800c0 ffff9d0f95d7fbc0: ffff9d0f8f3a20b8 ffff9d0fa74bea00 ffff9d0f95d7fbd0: ffff9d0f95d7fc38 ffffffffc03f085d #6 [ffff9d0f95d7fbd8] mlx5_core_destroy_mkey at ffffffffc03f085d [mlx5_core]
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要注意，reboot 正在释放的 mlx5_core_dev 是 ffff9d0fa74800c0，这个设备对应的 net_device 是：p3p1,而 23283 进程正在访问的 mlx5_core_dev 是 ffff9d0fa3c800c0 ，对应的是 p3p2。
crash> net NET_DEVICE NAME IP ADDRESS(ES)ffff9d0fc003e000 lo 127.0.0.1ffff9d1fad200000 p1p1 ffff9d0fa0700000 p1p2 ffff9d0fa00c0000 p3p1 对应的 mlx5_core_dev 是 ffff9d0fa74800c0ffff9d0fa0200000 p3p2 对应的 mlx5_core_dev 是 ffff9d0fa3c800c0
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我们看下目前还残留在 devices_kset 中的 device：
crash> p devices_ksetdevices_kset = $4 = (struct kset *) 0xffff9d1fbf4e70c0crash> p devices_kset.list$5 = { next = 0xffffffffb72f2a38, prev = 0xffff9d0fbe0ea130}
crash> list -H -o 0x18 0xffffffffb72f2a38 -s device.kobj.name >device.list
我们发现p3p1 与 p3p2均不在 device.list中，
[root@it202-seg-k8s-prod001-node-10-27-96-220 127.0.0.1-2020-12-07-10:58:06]# grep 0000:5e:00.0 device.list //caq:未找到 这个是 p3p1，当前reboot流程正在卸载。[root@it202-seg-k8s-prod001-node-10-27-96-220 127.0.0.1-2020-12-07-10:58:06]# grep 0000:5e:00.1 device.list //caq:未找到，这个是 p3p2,已经卸载完[root@it202-seg-k8s-prod001-node-10-27-96-220 127.0.0.1-2020-12-07-10:58:06]# grep 0000:3b:00.0 device.list //caq:这个mlx5设备还没unload kobj.name = 0xffff9d1fbe82aa70 "0000:3b:00.0",[root@it202-seg-k8s-prod001-node-10-27-96-220 127.0.0.1-2020-12-07-10:58:06]# grep 0000:3b:00.1 device.list //caq:这个mlx5设备还没unload kobj.name = 0xffff9d1fbe82aae0 "0000:3b:00.1",
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由于 p3p2 与 p3p1 均不在 device.list 中，而根据 pci_device_shutdown 的串行卸载流程，当前正在卸载的是 p3p1，所以很确定的是 23283 进程访问的是卸载后的 cmd_pool,根据前面描述的卸载流程 ：pci_device_shutdown-->shutdown-->mlx5_unload_one-->mlx5_cmd_cleanup-->dma_pool_destroy 此时的 pool 已经被释放了，pool 中的 dma_page 均无效的。
然后尝试 google 对应的 bug，查看到一个跟当前现象极为相似，redhat 遇到了类似的问题：https://access.redhat.com/solutions/5132931
但是，红帽在这个链接中认为解决了 uaf 的问题，合入的补丁却是：
commit 4cca96a8d9da0ed8217cfdf2aec0c3c8b88e8911Author: Parav Pandit <parav@mellanox.com>Date: Thu Dec 12 13:30:21 2019 +0200
diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.cindex 997cbfe..05b557d 100644--- a/drivers/infiniband/hw/mlx5/main.c+++ b/drivers/infiniband/hw/mlx5/main.c@@ -6725,6 +6725,8 @@ void __mlx5_ib_remove(struct mlx5_ib_dev *dev, const struct mlx5_ib_profile *profile, int stage) {+ dev->ib_active = false;+ /* Number of stages to cleanup */ while (stage) { stage--;
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敲黑板，三遍：这个合入是不能解决对应的 bug 的，比如如下的并发：我们用一个简单的图来表示一下并发处理：
CPU1 CPU2 dev_attr_show pci_device_shutdown speed_show shutdown mlx5_unload_one mlx5_detach_device mlx5_detach_interface mlx5e_detach mlx5e_detach_netdev mlx5e_nic_disable rtnl_lock mlx5e_close_locked clear_bit(MLX5E_STATE_OPENED, &priv->state);---只清理了这个bit rtnl_unlock rtnl_trylock---持锁成功后 netif_running 只是判断net_device.state的最低位 __ethtool_get_link_ksettings mlx5e_get_link_ksettings mlx5_query_port_ptys() mlx5_core_access_reg() mlx5_cmd_exec cmd_exec mlx5_alloc_cmd_msg mlx5_cmd_cleanup---清理dma_pool dma_pool_alloc---访问cmd.pool,触发crash
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所以如果要真正解决这个问题，还需要 netif_device_detach 中清理 __LINK_STATE_START 的 bit 位，或者在 speed_show 中判断一下 __LINK_STATE_PRESENT 位？如果考虑影响范围，不想动公共流程，则应该在 mlx5e_get_link_ksettings 中判断一下 __LINK_STATE_PRESENT。这个就留给喜欢跟社区打交道的同学去完善吧。
static void mlx5e_nic_disable(struct mlx5e_priv *priv){....... rtnl_lock(); if (netif_running(priv->netdev)) mlx5e_close(priv->netdev); netif_device_detach(priv->netdev); //caq:增加一下清理 __LINK_STATE_PRESENT位 rtnl_unlock();.......
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三、故障复现
1、竞态问题，可以制造类似上图 cpu1 与 cpu2 的竞争场景。
四、故障规避或解决
可能的解决方案是：
1、不要按照红帽https://access.redhat.com/solutions/5132931那样升级。
2、单独打补丁。
作者简介
Anqing
目前在 OPPO 混合云负责 linux 内核及容器，虚拟机等虚拟化方面的工作
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