硬件错误导致的crash
[683650.031028] BUG: unable to handle kernel paging request at 000000000001b790-----------------------------地址错误
[683650.031060] IP: [<ffffffff94b13520>] native_queued_spin_lock_slowpath+0x110/0x200
[683650.031089] PGD 8000005f702d4067 PUD 510c27a067 PMD 0
[683650.031109] Oops: 0002 [#1] SMP
[683650.031567] CPU: 40 PID: 474165 Comm: dfget Kdump: loaded Tainted: G ------------ T 3.10.0-957.27.2.el7.x86_64 #1
[683650.031599] Hardware name: Dell Inc. PowerEdge R640/0RJCR7, BIOS 1.6.13 12/17/2018
[683650.031621] task: ffff8d37d86ac100 ti: ffff8d4adbbdc000 task.ti: ffff8d4adbbdc000
[683650.031643] RIP: 0010:[<ffffffff94b13520>] [<ffffffff94b13520>] native_queued_spin_lock_slowpath+0x110/0x200
[683650.031673] RSP: 0018:ffff8d4adbbdfea0 EFLAGS: 00010006
[683650.031689] RAX: 000000000000175f RBX: ffff8d37d86ac100 RCX: 0000000001410000
[683650.031709] RDX: 000000000001b790 RSI: 00000000bafb5140 RDI: ffff8d88afab1048----------这个就是sighand_struct.siglock
[683650.031729] RBP: ffff8d4adbbdfea0 R08: ffff8d58bdf1b780 R09: 0000000000000000
[683650.031749] R10: 0000000000000008 R11: 0000000000000206 R12: ffff8d4adbbdfef0
[683650.031769] R13: 0000000000000000 R14: 0000000000000002 R15: 0000000000000000
[683650.031789] FS: 00007fb5b67fc700(0000) GS:ffff8d58bdf00000(0000) knlGS:0000000000000000
[683650.031812] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[683650.031828] CR2: 000000000001b790 CR3: 0000005f757a8000 CR4: 00000000007607e0
[683650.031849] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[683650.031869] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[683650.031889] PKRU: 55555554
[683650.031898] Call Trace:
[683650.031912] [<ffffffff9515e2cb>] queued_spin_lock_slowpath+0xb/0xf
[683650.031935] [<ffffffff9516c6a8>] _raw_spin_lock_irq+0x28/0x30
[683650.031955] [<ffffffff94ab0a97>] __set_current_blocked+0x37/0x70
[683650.031974] [<ffffffff94ab0c67>] sigprocmask+0x77/0xb0
[683650.032768] [<ffffffff94ab0d32>] SyS_rt_sigprocmask+0x92/0x100
[683650.033480] [<ffffffff95176ddb>] system_call_fastpath+0x22/0x27
[683650.034184] Code: 87 47 02 c1 e0 10 45 31 c9 85 c0 74 44 48 89 c2 c1 e8 13 48 c1 ea 0d 48 98 83 e2 30 48 81 c2 80 b7 01 00 48 03 14 c5 a0 bf 74 95 <4c> 89 02 41 8b 40 08 85 c0 75 0f 0f 1f 44 00 00 f3 90 41 8b 40
[683650.035684] RIP [<ffffffff94b13520>] native_queued_spin_lock_slowpath+0x110/0x200
[683650.036404] RSP <ffff8d4adbbdfea0>
[683650.037151] CR2: 000000000001b790
根据内核代码分析，对应的sighand_struct.siglock值不正确，导致异常。
crash> sighand_struct.siglock 0xffff8d88afab0840 -x
siglock = {
{
rlock = {
raw_lock = {
val = {
counter = 0x1415140
}
}
}
}
}
按照qspinlock的布局，最后一个8位应该是1，然后如果有人在等待锁，pending位应该位1，其次会有等待的cpu的编号记录。但是根据多年排查crash的经验，明显这个值是异常的。
由于这个是一把sighand公共锁，所以打印其他线程的锁如下：
crash> task_struct.sighand ffff8d88983da080
sighand = 0xffff8d88afeb0840-------------------------e就是1110
crash> task_struct.sighand ffff8d88983d8000
sighand = 0xffff8d88afeb0840
crash> task_struct.sighand ffff8d37d86ac100
sighand = 0xffff8d88afab0840------------------------a就是1010
仔细一点可以看出，这把锁发生了bit位翻转。这种情况等锁，就像在公交车站等一艘船，可能也就武汉能偶尔等到。
另外，这个bit翻转在ipmi和mce中都未看到异常。
