Date:   Mon, 15 Feb 2021 17:36:08 +0530
From:   Shashidhar Patil <shashidhar.patil@...il.com>
To:     linux-ext4@...r.kernel.org
Subject: jbd2 task hung in jbd2_journal_commit_transaction

Hi,
      We are seeing problem with many tasks hung in 'D' state and
stack output of jbd2 thread is hung at
jbd2_journal_commit_transaction().

The stack trace of jdb2 task is:

[<0>] jbd2_journal_commit_transaction+0x26e/0x1870^M
[<0>] kjournald2+0xc8/0x250^M
[<0>] kthread+0x105/0x140^M
[<0>] ret_from_fork+0x35/0x40^M
[<0>] 0xffffffffffffffff^M

The symptoms look similar to
https://www.spinics.net/lists/linux-ext4/msg53502.html.

The system has zswap configured with swap backing is an ext4 file.
There are oom kills recorded in the dmesg.

As per Theodore in the above link the issue is caused by a leaked
atomic handle. But one of the backtraces collected (below) points to
a.possile problem of cylic dependency.
This is explained in below steps
1. sys_write processing allocates atomic handle for journaling
2. as part of write processing page allocation is called.
3. Because of lack of page frames zswap gets invoked to free up a page frame.
4. zswap backup ram is full so it tries to free up some pages and
initiates a disk writeback. In this case the swap file is on the same
partition on which write() call is done.
5. Until the write request is processed the atomic handle is not
released(journal_stop)
6. The write transfer hangs in transaction_commit since there is an
open atomic handle.

Is this a possibility ? I have more logs captured with /proc/sysrq
which I can share as required.

Appreciate your help.


4,1707851,1121527990415,-; __schedule+0x3d6/0x8b0
4,1707852,1121527990416,-; schedule+0x36/0x80
4,1707853,1121527990417,-; io_schedule+0x16/0x40
4,1707854,1121527990418,-; wbt_wait+0x22f/0x380
4,1707855,1121527990419,-; ? trace_event_raw_event_wbt_timer+0x100/0x100
4,1707856,1121527990421,-; ? end_swap_bio_read+0xd0/0xd0
4,1707857,1121527990422,-; blk_mq_make_request+0x103/0x5b0
4,1707905,1121527990537,-; ? end_swap_bio_read+0xd0/0xd0
4,1707906,1121527990541,-; generic_make_request+0x122/0x2f0
4,1707907,1121527990544,-; submit_bio+0x73/0x140
4,1707908,1121527990547,-; ? submit_bio+0x73/0x140
4,1707909,1121527990549,-; ? get_swap_bio+0xcf/0x100
4,1707910,1121527990553,-; __swap_writepage+0x33f/0x3b0
4,1707911,1121527990555,-; ? lru_cache_add_file+0x37/0x40
4,1707912,1121527990558,-; ? lzo_decompress+0x38/0x70
4,1707913,1121527990561,-; zswap_writeback_entry+0x249/0x350
4,1707914,1121527990565,-; zbud_zpool_evict+0x31/0x40
4,1707915,1121527990568,-; zbud_reclaim_page+0x1e9/0x250
4,1707916,1121527990571,-; zbud_zpool_shrink+0x3b/0x60
4,1707917,1121527990574,-; zpool_shrink+0x1c/0x20
4,1707918,1121527990577,-; zswap_frontswap_store+0x274/0x530
4,1707919,1121527990580,-; __frontswap_store+0x78/0x100
4,1707920,1121527990584,-; swap_writepage+0x3f/0x80
4,1707921,1121527990587,-; pageout.isra.53+0x1e6/0x340
4,1707922,1121527990590,-; shrink_page_list+0x992/0xbe0
4,1707923,1121527990593,-; shrink_inactive_list+0x2af/0x5f0
4,1707924,1121527990596,-; ? _find_next_bit+0x40/0x70
4,1707925,1121527990599,-; shrink_node_memcg+0x36f/0x7f0
4,1707926,1121527990603,-; shrink_node+0xe1/0x310
4,1707927,1121527990606,-; ? shrink_node+0xe1/0x310
4,1707928,1121527990609,-; do_try_to_free_pages+0xee/0x360
4,1707929,1121527990612,-; try_to_free_pages+0xf1/0x1c0
4,1707930,1121527990614,-; __alloc_pages_slowpath+0x399/0xe90
4,1707931,1121527990616,-; __alloc_pages_nodemask+0x289/0x2d0
4,1707932,1121527990618,-; alloc_pages_current+0x6a/0xe0
4,1707933,1121527990619,-; __page_cache_alloc+0x86/0x90
4,1707934,1121527990620,-; pagecache_get_page+0x88/0x2c0
4,1707935,1121527990621,-; grab_cache_page_write_begin+0x23/0x40
4,1707936,1121527990623,-; ext4_da_write_begin+0xd8/0x460
4,1707937,1121527990624,-; generic_perform_write+0xba/0x1b0
4,1707938,1121527990625,-; __generic_file_write_iter+0x1a6/0x1f0
4,1707939,1121527990627,-; ext4_file_write_iter+0xc4/0x3b0
4,1707940,1121527990629,-; ? __handle_mm_fault+0xa67/0x1240
4,1707941,1121527990630,-; ? __switch_to_asm+0x41/0x70
4,1707942,1121527990632,-; new_sync_write+0xe5/0x140
4,1707943,1121527990633,-; __vfs_write+0x29/0x40
4,1707944,1121527990635,-; vfs_write+0xb8/0x1b0
4,1707945,1121527990636,-; ? syscall_trace_enter+0x1d6/0x2f0
4,1707946,1121527990637,-; SyS_write+0x5c/0xe0
4,1707947,1121527990639,-; do_syscall_64+0x73/0x130
4,1707948,1121527990640,-; entry_SYSCALL_64_after_hwframe+0x3d/0xa2

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