8556395.925003] XFS (sdi): xfs_log_force: error -5 returned. [8556407.425047] INFO: task umount:19286 blocked for more than 1200 seconds.----这个默认是120，该环境上是被人为设置1200 [8556407.425653] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [8556407.426050] umount D ffff881fffdd47c0 0 19286 19283 0x00000080------------------------19286是pid，19283是ppid [8556407.426056] ffff883e39587d80 0000000000000082 ffff883e39587fd8 ffff883e39587fd8 [8556407.426066] ffff883e39587fd8 00000000000147c0 ffff881fd3260000 ffff881f860fec80 [8556407.426072] ffff883ed79e1a20 ffff881f860fecc0 ffff881f860fece8 ffff881f860fec90------------这12个64位的值为栈里的值 [8556407.426078] Call Trace: [8556407.426092] [<ffffffff8163e879>] schedule+0x29/0x70 [8556407.426137] [<ffffffffa07c6cd1>] xfs_ail_push_all_sync+0xc1/0x110 [xfs] [8556407.426143] [<ffffffff810a7610>] ? wake_up_atomic_t+0x30/0x30 [8556407.426165] [<ffffffffa07b1b98>] xfs_unmountfs+0x68/0x190 [xfs] [8556407.426186] [<ffffffffa07b267b>] ? xfs_mru_cache_destroy+0x6b/0x90 [xfs] [8556407.426204] [<ffffffffa07b4a52>] xfs_fs_put_super+0x32/0x90 [xfs] [8556407.426211] [<ffffffff811e3026>] generic_shutdown_super+0x56/0xe0-------已经执行完fsnotify_umount_inodes [8556407.426215] [<ffffffff811e3477>] kill_block_super+0x27/0x70 [8556407.426218] [<ffffffff811e37b9>] deactivate_locked_super+0x49/0x60 [8556407.426222] [<ffffffff811e3db6>] deactivate_super+0x46/0x60 [8556407.426229] [<ffffffff81200d25>] mntput_no_expire+0xc5/0x120 [8556407.426234] [<ffffffff812025cb>] SyS_umount+0x15b/0x5b0 [8556407.426239] [<ffffffff81649909>] system_call_fastpath+0x16/0x1b [8556407.426242] sending NMI to all CPUs:
对应的函数为：
/* * Push out all items in the AIL immediately and wait until the AIL is empty. */ void xfs_ail_push_all_sync( struct xfs_ail *ailp) { struct xfs_log_item *lip; DEFINE_WAIT(wait); spin_lock(&ailp->xa_lock); while ((lip = xfs_ail_max(ailp)) != NULL) { prepare_to_wait(&ailp->xa_empty, &wait, TASK_UNINTERRUPTIBLE); ailp->xa_target = lip->li_lsn; wake_up_process(ailp->xa_task); spin_unlock(&ailp->xa_lock); schedule(); spin_lock(&ailp->xa_lock); } spin_unlock(&ailp->xa_lock); finish_wait(&ailp->xa_empty, &wait); }
排查的时候走了弯路，因为看的是：
crash> dis -l xfs_ail_push_all_sync+0xc1 /usr/src/debug/kernel-3.10.0-327.22.2.el7/linux-3.10.0-327.22.2.el7.x86_64/include/linux/spinlock.h: 293 0xffffffffa07c6cd1 <xfs_ail_push_all_sync+193>: mov %r13,%rdi
所以想当然地认为在第一个 获取spinlock的地方，
spin_lock(&ailp->xa_lock);---------以为在这hung住 while ((lip = xfs_ail_max(ailp)) != NULL) {
然后查找这把锁：
crash> struct super_block.s_fs_info ffff883f7fe67800 s_fs_info = 0xffff883f7fe67000 crash> mod -s xfs MODULE NAME SIZE OBJECT FILE ffffffffa0803d40 xfs 939714 /lib/modules/3.10.0-327.22.2.el7.x86_64/kernel/fs/xfs/xfs.ko crash> struct -xo xfs_mount.m_ail 0xffff883f7fe67000 struct xfs_mount { [ffff883f7fe67010] struct xfs_ail *m_ail; } struct xfs_mount.m_ail 0xffff883f7fe67000 m_ail = 0xffff881f860fec80 crash> struct -xo xfs_ail.xa_lock 0xffff881f860fec80 struct xfs_ail { [ffff881f860fecc0] spinlock_t xa_lock; }
而且这把锁的值是：
crash> struct xfs_ail.xa_lock 0xffff881f860fec80 xa_lock = { { rlock = { raw_lock = { { head_tail = 2406518640, tickets = { head = 36720, tail = 36720 } } } } } }
我一看到这个是非0值，想当然认为是被持有了，为了验证我的想法，我甚至随便找了一把锁查看它的值，点背的时候，喝凉水都塞牙，我随手选择的锁是：
crash> p gc_lock gc_lock = $1 = { { rlock = { raw_lock = { { head_tail = 0, tickets = { head = 0, tail = 0 } } } } } }
后来仔细看了在没有开启 CONFIG_QUEUED_SPINLOCKS 的情况下，锁的定义才是如此，否则的话，是如下：
#ifndef __GENKSYMS__ typedef struct qspinlock { atomic_t val; } arch_spinlock_t; #else typedef u32 __ticketpair_t; typedef struct arch_spinlock { union { __ticketpair_t head_tail; struct __raw_tickets { __ticket_t head, tail; } tickets; }; } arch_spinlock_t; #endif
所以要么0，要么1的情况只适合于第一种定义，以前因为业务默认配置的config问题，查的锁相关的crash，大多是第一种定义，但是当时没注意到这个细节，只是简单扫了一眼，浪费我两个小时，所以下盘不稳总会摔。
查看running状态的都没有持有这把锁，（其实按照第二种定义，是正常的，因为此时本就没人持有这把锁，因为head和tail相等）比较奇怪，后来找同事讨论，同事认为是while循环没跳出，所以获取锁的那行是schedule下面那行，还没有执行。
想起来自己曾经写过的博客《https://www.cnblogs.com/10087622blog/p/9558024.html》,应该是如此
void xfs_ail_push_all_sync( struct xfs_ail *ailp) { struct xfs_log_item *lip; DEFINE_WAIT(wait); spin_lock(&ailp->xa_lock); while ((lip = xfs_ail_max(ailp)) != NULL) { prepare_to_wait(&ailp->xa_empty, &wait, TASK_UNINTERRUPTIBLE); ailp->xa_target = lip->li_lsn; wake_up_process(ailp->xa_task); spin_unlock(&ailp->xa_lock); schedule();--------------------这个和while循环一直跳不出去， spin_lock(&ailp->xa_lock); } spin_unlock(&ailp->xa_lock); finish_wait(&ailp->xa_empty, &wait); }
跳不出去的原因跟io相关，也就是wake_up 相关的内核线程之后，内核线程还是没有完成对应的任务：
crash> struct xfs_ail.xa_task 0xffff881f860fec80 xa_task = 0xffff883f8901dc00 crash> task_struct.pid 0xffff883f8901dc00 pid = 42726 crash> set 42726 PID: 42726 COMMAND: "xfsaild/sdi" TASK: ffff883f8901dc00 [THREAD_INFO: ffff881f3d828000] CPU: 17 STATE: TASK_INTERRUPTIBLE crash> bt PID: 42726 TASK: ffff883f8901dc00 CPU: 17 COMMAND: "xfsaild/sdi" #0 [ffff881f3d82bcd0] __schedule at ffffffff8163df9b #1 [ffff881f3d82bd38] schedule at ffffffff8163e879 #2 [ffff881f3d82bd48] schedule_timeout at ffffffff8163c295 #3 [ffff881f3d82bdf8] xfsaild at ffffffffa07c6a4f [xfs] #4 [ffff881f3d82bec8] kthread at ffffffff810a661f #5 [ffff881f3d82bf50] ret_from_fork at ffffffff81649858
xfsaild 无法完成的原因也是因为IO异常:
附部分相关io异常的message日志：
kernel: sd 5:0:8:0: [sdi] CDB: Read(16) 88 00 00 00 00 00 03 4c b0 48 00 00 00 08 00 00 kernel: sd 5:0:8:0: [sdi] CDB: Read(16) 88 00 00 00 00 00 15 32 8a 50 00 00 03 30 00 00 kernel: blk_update_request: I/O error, dev sdi, sector 355634560 kernel: sd 5:0:8:0: rejecting I/O to offline device kernel: XFS (sdi): metadata I/O error: block 0xee173de0 ("xfs_trans_read_buf_map") error 5 numblks 8 kernel: XFS (sdi): metadata I/O error: block 0x15da29d90 ("xfs_trans_read_buf_map") error 5 numblks 32 kernel: sd 5:0:8:0: rejecting I/O to offline device kernel: XFS (sdi): xfs_imap_to_bp: xfs_trans_read_buf() returned error -5. kernel: XFS (sdi): metadata I/O error: block 0xeca8a480 ("xfs_trans_read_buf_map") error 5 numblks 8 kernel: sd 5:0:8:0: rejecting I/O to offline device kernel: sd 5:0:8:0: rejecting I/O to offline device
对应的bug解决可以参照：https://bugzilla.redhat.com/show_bug.cgi?id=1267042