Re: [bug report] Hang on sync after dd

[Ming Lei <ming.lei@redhat.com>]

On Mon, Nov 30, 2020 at 11:22:33AM +0000, John Garry wrote:
> Hi all,
> 
> 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"
> 
> 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
> 
> The issue was reported here originally:
> https://lore.kernel.org/linux-ext4/4d18326e-9ca2-d0cb-7cb8-cb56981280da@hisilicon.com/
> 
> But it looks like issue related to recent work for SCSI MQ.
> 
> They can only create with hisi_sas v3 hw. I could not create with megaraid
> sas on the same dev platform or hisi_sas on a similar dev board.
> 
> Reverting "scsi: core: Only re-run queue in scsi_end_request() if device
> queue is busy" seems solve the issue. Also, checking out to patch prior to
> "scsi: hisi_sas: Switch v3 hw to MQ" seems to not have the issue.

If the issue can be reproduced, you may try the following patch:

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 60c7a7d74852..f95bd0e5006e 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -602,6 +602,9 @@ static bool scsi_end_request(struct request *req, blk_status_t error,
 
        __blk_mq_end_request(req, error);
 
+       if (unlikely(req->end_io))
+               smp_mb();
+
        scsi_run_queue_async(sdev);
 
        percpu_ref_put(&q->q_usage_counter);


Thanks, 
Ming