Linux内核Bug怎么解决

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一个bug, 有人升级内核到V5.10-rcX之后，执行dd和sync之后看到进程有hang住的情况:

Some guys internally upgraded to v5.10-rcX and start to see a hang after  dd + sync for a large file: - mount /dev/sda1 (ext4 filesystem) to directory /mnt; - run "if=/dev/zero of=test1 bs=1M count=2000" on directory /mnt; - run "sync"

系统提示打印hang住进程的堆栈信息:

and get:  [  367.912761] INFO: task jbd2/sdb1-8:3602 blocked for more than 120 seconds. [  367.919618]       Not tainted 5.10.0-rc1-109488-g32ded76956b6 #948 [  367.925776] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [  367.933579] task:jbd2/sdb1-8     state:D stack:    0 pid: 3602 ppid:     2 flags:0x00000028 [  367.941901] Call trace: [  367.944351] __switch_to+0xb8/0x168 [  367.947840] __schedule+0x30c/0x670 [  367.951326] schedule+0x70/0x108 [  367.954550] io_schedule+0x1c/0xe8 [  367.957948] bit_wait_io+0x18/0x68 [  367.961346] __wait_on_bit+0x78/0xf0 [  367.964919] out_of_line_wait_on_bit+0x8c/0xb0 [  367.969356] __wait_on_buffer+0x30/0x40 [  367.973188] jbd2_journal_commit_transaction+0x1370/0x1958 [  367.978661] kjournald2+0xcc/0x260 [  367.982061] kthread+0x150/0x158 [  367.985288] ret_from_fork+0x10/0x34 [  367.988860] INFO: task sync:3823 blocked for more than 120 seconds. [  367.995102]       Not tainted 5.10.0-rc1-109488-g32ded76956b6 #948 [  368.001265] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [  368.009067] task:sync            state:D stack:    0 pid: 3823 ppid: 3450 flags:0x00000009 [  368.017397] Call trace: [  368.019841] __switch_to+0xb8/0x168 [  368.023320] __schedule+0x30c/0x670 [  368.026804] schedule+0x70/0x108 [  368.030025] jbd2_log_wait_commit+0xbc/0x158 [  368.034290] ext4_sync_fs+0x188/0x1c8 [  368.037947] sync_fs_one_sb+0x30/0x40 [  368.041606] iterate_supers+0x9c/0x138 [  368.045350] ksys_sync+0x64/0xc0 [  368.048569] __arm64_sys_sync+0x10/0x20 [  368.052398] el0_svc_common.constprop.3+0x68/0x170 [  368.057177] do_el0_svc+0x24/0x90 [  368.060482] el0_sync_handler+0x118/0x168 [  368.064478]  el0_sync+0x158/0x180

并反馈8号硬队列绑定的第100号cpu上派发队列和完成队列不一致，但是没有inflight的情况，因为这个情况，苦恼了三天三夜，头发掉满了整个键盘。

estuary:/sys/kernel/debug/block/sda/hctx8$ cat cpu100/dispatched 3 0 estuary:/sys/kernel/debug/block/sda/hctx8$ cat cpu100/completed 2 0 On cpu100, it seems completed is less than number dispatched. /sys/devices/pci0000:74/0000:74:02.0/host0/port-0:0/end_device-0:0/target0:0:0/0:0:0:0/block/sda/sda1/inflight),  the number of inflight is 0.

然后Ming Lei (自带音响出场)给出意见,需要收集/sys/kernel/debug/block/sda 目录和/sys/block/sda/device 目录下所有文件的输出:

hello chenxiang, Can you collect the debugfs log via the following commands after the io hang is triggered?  1) debugfs log:          (cd /sys/kernel/debug/block/sda && find . -type f -exec grep -aH . {} \;)  2) scsi sysfs info:          (cd /sys/block/sda/device && find . -type f -exec grep -aH . {} \;)  Suppose the disk is /dev/sda.

chenxiang 反馈:

~$ cd /sys/kernel/debug/block/sdb && find . -type f -exec grep  -aH . {} \; ... ./hctx9/tags:cleared=3891 ./hctx9/tags:bits_per_word=64 ./hctx9/tags:map_nr=63 ./hctx9/tags:alloc_hint={3264, 3265, 0, 3731, 2462, 842, 0, 0, 1278, 27,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2424, 0, 0, 0,  346, 3, 3191, 235, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 88, 0, 0, 285, 0, 0, 0, 0, 0, 0, 0, 0, 0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1165, 538, 0,  372, 277, 3476, 0, 0, 0, 111, 0, 2081, 0, 112, 0, 0, 0, 0, 904, 1127, 0,  0, 0, 113, 0, 0, 0, 0, 0, 0, 321, 0} ./hctx9/tags:wake_batch=8 ./hctx9/tags:wake_index=7 ./hctx9/tags:ws_active=0 ./hctx9/tags:ws={ ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:   {.wait_cnt=8, .wait=inactive}, ./hctx9/tags:} ./hctx9/tags:round_robin=1 ./hctx9/tags:min_shallow_depth=4294967295 ./hctx9/ctx_map:00000000: 00 ...

Ming Lei 大神看了一下debug输出，小喝一杯大红袍，就直接建议去测试这个patch:

Please try the following patch:  diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 60c7a7d74852..03c6d0620bfd 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1703,8 +1703,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,          break;      case BLK_STS_RESOURCE:      case BLK_STS_ZONE_RESOURCE: -        if (atomic_read(&sdev->device_busy) || -            scsi_device_blocked(sdev)) +        if (scsi_device_blocked(sdev))              ret = BLK_STS_DEV_RESOURCE;          break;      default:

chenxiang 测试反馈之后，问题解决，内心洋溢着Linux从业者单纯的喜悦，眼神中流露出满满的崇敬之情，恨不得以身相许:

I have tested the patch  100+ times on two envirments(on which the issue  occurs frequently before), and the issue doesn't occur.

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