bcache: fix oops in cache_set_flush · Pull Request !13205 · openEuler/kernel

解决5.10内核 bcache在硬盘上有旧的损坏数据，读数据错误导致kernel panic问题。
在openEuler 22.03 SP3上验证通过。
关联issue:https://gitee.com/openeuler/kernel/issues/IB3YQZ
```mermaid
graph TD
    register_cache_set --> run_cache_set
    run_cache_set --> prio_read
    prio_read--> bch_cache_set_unregister
    bch_cache_set_unregister --> bch_cache_set_stop
    bch_cache_set_stop  -.-> __cache_set_unregister

__cache_set_unregister --> cache_set_flush
    subgraph register_cache_set 
        run_cache_set
        bch_cache_set_unregister
        bch_cache_set_stop
    end

subgraph run_cache_set 
        prio_read
    end

cache_set_flush --> list_add

```
```
crash> dis  cache_set_flush
0xffffbe50121fa434 <cache_set_flush>:   mov     x9, x30
0xffffbe50121fa438 <cache_set_flush+4>: nop
0xffffbe50121fa43c <cache_set_flush+8>: paciasp
0xffffbe50121fa440 <cache_set_flush+12>:        stp     x29, x30, [sp, #-80]!
0xffffbe50121fa444 <cache_set_flush+16>:        mov     x29, sp
0xffffbe50121fa448 <cache_set_flush+20>:        stp     x21, x22, [sp, #32]
0xffffbe50121fa44c <cache_set_flush+24>:        mov     x21, x0
0xffffbe50121fa450 <cache_set_flush+28>:        sub     x22, x0, #0x4a8
0xffffbe50121fa454 <cache_set_flush+32>:        stp     x19, x20, [sp, #16]
0xffffbe50121fa458 <cache_set_flush+36>:        add     x0, x22, #0x128
0xffffbe50121fa45c <cache_set_flush+40>:        stp     x23, x24, [sp, #48]
0xffffbe50121fa460 <cache_set_flush+44>:        ldur    x24, [x21, #-56]
0xffffbe50121fa464 <cache_set_flush+48>:        bl      0xffffbe50121f8e88 <bch_cache_accounting_destroy>
0xffffbe50121fa468 <cache_set_flush+52>:        add     x0, x22, #0xc0
0xffffbe50121fa46c <cache_set_flush+56>:        bl      0xffffbe501220b890 <bcache_device_free+2504>
0xffffbe50121fa470 <cache_set_flush+60>:        add     x0, x22, #0x60
0xffffbe50121fa474 <cache_set_flush+64>:        bl      0xffffbe501220b6e0 <bcache_device_free+2072>
0xffffbe50121fa478 <cache_set_flush+68>:        ldr     x0, [x22, #2256]
0xffffbe50121fa47c <cache_set_flush+72>:        cbz     x0, 0xffffbe50121fa48c <cache_set_flush+88>
0xffffbe50121fa480 <cache_set_flush+76>:        cmn     x0, #0x1, lsl #12
0xffffbe50121fa484 <cache_set_flush+80>:        b.hi    0xffffbe50121fa48c <cache_set_flush+88>  // b.pmore
0xffffbe50121fa488 <cache_set_flush+84>:        bl      0xffffbe501220b56c <bcache_device_free+1700>
0xffffbe50121fa48c <cache_set_flush+88>:        add     x0, x22, #0x8, lsl #12
0xffffbe50121fa490 <cache_set_flush+92>:        ldr     x20, [x0, #17656]
0xffffbe50121fa494 <cache_set_flush+96>:        cmn     x20, #0x1, lsl #12
0xffffbe50121fa498 <cache_set_flush+100>:       b.hi    0xffffbe50121fa4d8 <cache_set_flush+164>  // b.pmore
0xffffbe50121fa49c <cache_set_flush+104>:       str     x25, [sp, #64]
0xffffbe50121fa4a0 <cache_set_flush+108>:       add     x19, x20, #0x200
0xffffbe50121fa4a4 <cache_set_flush+112>:       add     x25, x21, #0x360
0xffffbe50121fa4a8 <cache_set_flush+116>:       mov     x0, x19
0xffffbe50121fa4ac <cache_set_flush+120>:       ldr     x23, [x21, #864]
0xffffbe50121fa4b0 <cache_set_flush+124>:       mov     x1, x25
0xffffbe50121fa4b4 <cache_set_flush+128>:       mov     x2, x23
0xffffbe50121fa4b8 <cache_set_flush+132>:       bl      0xffffbe501220b440 <bcache_device_free+1400>
0xffffbe50121fa4bc <cache_set_flush+136>:       tst     w0, #0xff
0xffffbe50121fa4c0 <cache_set_flush+140>:       b.eq    0xffffbe50121fa5a0 <cache_set_flush+364>  // b.none
0xffffbe50121fa4c4 <cache_set_flush+144>:       str     x19, [x23, #8]
0xffffbe50121fa4c8 <cache_set_flush+148>:       str     x23, [x20, #512]
```

```
crash> dis cache_set_flush+0x94
0xffffbe50121fa4c8 <cache_set_flush+148>:       str     x23, [x20, #512]
```
  从 cache_set_flush 的反汇编可以看出，在执行 ldr x20, [x0, #17656] 时，x0 是指向 cache_set 结构体的指针，而 x20 存储的是从该结构体偏移 17656 地址读取的内容，也就是cache_set结构体的root成员地址。
  vmcore-message中显示x20是 x20: 0000000000000000，操作list时导致kernel panic。
  崩溃的原因由于 `cache_set_flush` 函数中访问了未初始化或空的指针`x20`，需要检查 `cache_set` 结构体的初始化过程，确认相关指针是否正确设置。如果指针为 `NULL` 或无效，则需要修复初始化过程以避免这种错误。

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