Hello! On Mon 09-11-20 15:11:58, Chris Friesen wrote: > I'm running a 3.10.0-1127.rt56.1093 CentOS kernel. I realize you don't > support this particular kernel but I'm hoping for some general pointers. > > I've got a system with four "housekeeping" CPUs, with rcu_nocbs and > hohz_full used to reduce system overhead on the "application" CPUs, with > four CPUs set as "isolcpus" to try and isolate them even further. I have a > crashdump vmcore file from a softdog expiry when the process that pets the > softdog hung trying to write to /dev/log after the unix socket backlog had > been reached. > > I can see a "jbd2/nvme2n1p4-" process that appears to be hung for over 9 > minutes waiting to commit a transaction. /dev/nvme2n1p4 corresponds to the > root filesystem. The "ps" and "bt" output from the crashdump are below. > syslog-ng is also blocked waiting on filesystem access, and there are other > tasks also blocked on disk, including a few jbd2 tasks that are associated > with device mapper. Yeah, 9 minutes seems far too long. > Can anyone give some suggestions on how to track down what's causing the > delay here? I suspect there's a race condition somewhere similar to what > happened with https://access.redhat.com/solutions/3226391, although that one > was specific to device-mapper and the root filesystem here is directly on > the nvme device. Sadly I don't have access to RH portal to be able to check what that hang was about... > crash> ps -m 930 > [0 00:09:11.694] [UN] PID: 930 TASK: ffffa14b5f9032c0 CPU: 1 COMMAND: > "jbd2/nvme2n1p4-" > Are the tasks below the only ones hanging in D state (UN state in crash)? Because I can see processes are waiting for the locked buffer but it is unclear who is holding the buffer lock... > crash> bt 930 > PID: 930 TASK: ffffa14b5f9032c0 CPU: 1 COMMAND: "jbd2/nvme2n1p4-" > #0 [ffffa14b5ff0ba20] __schedule at ffffffffafe1b959 > #1 [ffffa14b5ff0bab0] schedule at ffffffffafe1be80 > #2 [ffffa14b5ff0bac8] schedule_timeout at ffffffffafe19d4c > #3 [ffffa14b5ff0bb70] io_schedule_timeout at ffffffffafe1ab6d > #4 [ffffa14b5ff0bba0] io_schedule at ffffffffafe1ac08 > #5 [ffffa14b5ff0bbb0] bit_wait_io at ffffffffafe1a561 > #6 [ffffa14b5ff0bbc8] __wait_on_bit at ffffffffafe1a087 > #7 [ffffa14b5ff0bc08] out_of_line_wait_on_bit at ffffffffafe1a1f1 > #8 [ffffa14b5ff0bc80] __wait_on_buffer at ffffffffaf85068a > #9 [ffffa14b5ff0bc90] jbd2_journal_commit_transaction at ffffffffc0e543fc > [jbd2] > #10 [ffffa14b5ff0be48] kjournald2 at ffffffffc0e5a6ad [jbd2] > #11 [ffffa14b5ff0bec8] kthread at ffffffffaf6ad781 > #12 [ffffa14b5ff0bf50] ret_from_fork_nospec_begin at ffffffffafe1fe5d > > Possibly of interest, syslog-ng is also blocked waiting on filesystem > access: > > crash> bt 1912 > PID: 1912 TASK: ffffa14b62dc2610 CPU: 1 COMMAND: "syslog-ng" > #0 [ffffa14b635b7980] __schedule at ffffffffafe1b959 > #1 [ffffa14b635b7a10] schedule at ffffffffafe1be80 > #2 [ffffa14b635b7a28] schedule_timeout at ffffffffafe19d4c > #3 [ffffa14b635b7ad0] io_schedule_timeout at ffffffffafe1ab6d > #4 [ffffa14b635b7b00] io_schedule at ffffffffafe1ac08 > #5 [ffffa14b635b7b10] bit_wait_io at ffffffffafe1a561 > #6 [ffffa14b635b7b28] __wait_on_bit at ffffffffafe1a087 > #7 [ffffa14b635b7b68] out_of_line_wait_on_bit at ffffffffafe1a1f1 > #8 [ffffa14b635b7be0] do_get_write_access at ffffffffc0e51e94 [jbd2] > #9 [ffffa14b635b7c80] jbd2_journal_get_write_access at ffffffffc0e521b7 > [jbd2] > #10 [ffffa14b635b7ca0] __ext4_journal_get_write_access at ffffffffc0eb8e31 > [ext4] > #11 [ffffa14b635b7cd0] ext4_reserve_inode_write at ffffffffc0e87fa0 [ext4] > #12 [ffffa14b635b7d00] ext4_mark_inode_dirty at ffffffffc0e8801e [ext4] > #13 [ffffa14b635b7d58] ext4_dirty_inode at ffffffffc0e8bc40 [ext4] > #14 [ffffa14b635b7d78] __mark_inode_dirty at ffffffffaf84855d > #15 [ffffa14b635b7da8] ext4_setattr at ffffffffc0e8b558 [ext4] > #16 [ffffa14b635b7e18] notify_change at ffffffffaf8363fc > #17 [ffffa14b635b7e60] chown_common at ffffffffaf8128ac > #18 [ffffa14b635b7f08] sys_fchown at ffffffffaf813fb7 > #19 [ffffa14b635b7f50] tracesys at ffffffffafe202a8 (via system_call) > > One of the hung jbd2 tasks associated with device mapper: > > crash> bt 1489 > PID: 1489 TASK: ffffa14b641f0000 CPU: 1 COMMAND: "jbd2/dm-0-8" > #0 [ffffa14b5fab7a20] __schedule at ffffffffafe1b959 > #1 [ffffa14b5fab7ab0] schedule at ffffffffafe1be80 > #2 [ffffa14b5fab7ac8] schedule_timeout at ffffffffafe19d4c > #3 [ffffa14b5fab7b70] io_schedule_timeout at ffffffffafe1ab6d > #4 [ffffa14b5fab7ba0] io_schedule at ffffffffafe1ac08 > #5 [ffffa14b5fab7bb0] bit_wait_io at ffffffffafe1a561 > #6 [ffffa14b5fab7bc8] __wait_on_bit at ffffffffafe1a087 > #7 [ffffa14b5fab7c08] out_of_line_wait_on_bit at ffffffffafe1a1f1 > #8 [ffffa14b5fab7c80] __wait_on_buffer at ffffffffaf85068a > #9 [ffffa14b5fab7c90] jbd2_journal_commit_transaction at ffffffffc0e543fc > [jbd2] > #10 [ffffa14b5fab7e48] kjournald2 at ffffffffc0e5a6ad [jbd2] > #11 [ffffa14b5fab7ec8] kthread at ffffffffaf6ad781 > #12 [ffffa14b5fab7f50] ret_from_fork_nospec_begin at ffffffffafe1fe5d > > Thanks, > > Chris -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
