On Wed, Apr 02, 2025 at 06:30:34PM +0000, Swarna Prabhu wrote:
> Testing generic/750 with older kernels indicated that more work has to
> be done, since we were able to reproduce a hang with v6.10-rc7 with 2.5
> hours soak duration. We tried to reproduce the same issue on v6.12 and could
> no longer reproduce the original hang. This motivated us to identify the commit
> 2e6506e1c4ee ("mm/migrate: fix deadlock in migrate_pages_batch() on large folios")
> that fixes the originally reported deadlock hang annotated as pending work
> to evaluate on generic/750. Hence if you are using kernel older than v6.11-rc4
> this commit is needed.
>
> Below is the kernel trace collected on v6.10-rc7 without the above
> commit and CONFGI_PROVE_LOCKING enabled:
>
> [ 8942.920967] ret_from_fork_asm+0x1a/0x30
> [ 8942.921450] </TASK>
> [ 8942.921711] INFO: task 750:2532 blocked for more than 241 seconds. [ 8942.922413] Not tainted 6.10.0-rc7 #9
> [ 8942.922894] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 8942.923770] task:750 state:D stack:0 pid:2532 tgid:2532 ppid:2349 flags:0x00004002 [ 8942.924820] Call Trace:
> [ 8942.925109] <TASK>
> [ 8942.925362] __schedule+0x465/0xe10
> [ 8942.925756] schedule+0x39/0x140
> [ 8942.926114] io_schedule+0x42/0x70
> [ 8942.926493] folio_wait_bit_common+0x10e/0x330
> [ 8942.926986] ? __pfx_wake_page_function+0x10/0x10
> [ 8942.927506] migrate_pages_batch+0x765/0xeb0
> [ 8942.927986] ? __pfx_compaction_alloc+0x10/0x10
> [ 8942.928488] ? __pfx_compaction_free+0x10/0x10
> [ 8942.928983] migrate_pages+0xbfd/0xf50
> [ 8942.929377] ? __pfx_compaction_alloc+0x10/0x10
> [ 8942.929838] ? __pfx_compaction_free+0x10/0x10
> [ 8942.930553] compact_zone+0xa4d/0x11d0
> [ 8942.930936] ? rcu_is_watching+0xd/0x40
> [ 8942.931332] compact_node+0xa9/0x120
> [ 8942.931704] sysctl_compaction_handler+0x71/0xd0
> [ 8942.932177] proc_sys_call_handler+0x1b8/0x2d0
> [ 8942.932641] vfs_write+0x281/0x530
> [ 8942.932993] ksys_write+0x67/0xf0
> [ 8942.933381] do_syscall_64+0x69/0x140
> [ 8942.933822] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 8942.934415] RIP: 0033:0x7f8a460215c7
> [ 8942.934843] RSP: 002b:00007fff75cf7bb0 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
> [ 8942.935720] RAX: ffffffffffffffda RBX: 00007f8a45f8f740 RCX: 00007f8a460215c7
> [ 8942.936550] RDX: 0000000000000002 RSI: 000055e89e3a7790 RDI: 0000000000000001
> [ 8942.937405] RBP: 000055e89e3a7790 R08: 0000000000000000 R09: 0000000000000000 [ 8942.938236] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
> [ 8942.939068] R13: 00007f8a4617a5c0 R14: 00007f8a46177e80 R15: 0000000000000000
> [ 8942.939902] </TASK>
> [ 8942.940169] Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings
> [ 8942.941150] INFO: lockdep is turned off.
>
> With the commit cherry picked to v6.10-rc7 , the test passes
> successfully without any hang/deadlock, however
> with CONFIG_PROVE_LOCKING enabled we do see the below trace for the
> passing case:
>
> BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> turning off the locking correctness validator.
> CPU: 1 PID: 2959 Comm: kworker/u34:5 Not tainted 6.10.0-rc7+ #12
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2024.11-5 01/28/2025
> Workqueue: btrfs-endio-write btrfs_work_helper [btrfs]
> Call Trace:
> <TASK>
> dump_stack_lvl+0x68/0x90
> __lock_acquire.cold+0x186/0x1b1
> lock_acquire+0xd6/0x2e0
> ? btrfs_get_alloc_profile+0x27/0x90 [btrfs]
> seqcount_lockdep_reader_access+0x70/0x90 [btrfs]
> ? btrfs_get_alloc_profile+0x27/0x90 [btrfs]
> btrfs_get_alloc_profile+0x27/0x90 [btrfs]
> btrfs_reserve_extent+0xa9/0x290 [btrfs]
> btrfs_alloc_tree_block+0xa5/0x520 [btrfs]
> ? lockdep_unlock+0x5e/0xd0
> ? __lock_acquire+0xc6f/0x1fa0
> btrfs_force_cow_block+0x111/0x5f0 [btrfs]
> btrfs_cow_block+0xcc/0x2d0 [btrfs]
> btrfs_search_slot+0x502/0xd00 [btrfs]
> ? stack_depot_save_flags+0x24/0x8a0
> btrfs_lookup_file_extent+0x48/0x70 [btrfs]
> btrfs_drop_extents+0x108/0xce0 [btrfs]
> ? _raw_spin_unlock_irqrestore+0x35/0x60
> ? __create_object+0x5e/0x90
> ? rcu_is_watching+0xd/0x40
> ? kmem_cache_alloc_noprof+0x280/0x320
> insert_reserved_file_extent+0xea/0x3a0 [btrfs]
> ? btrfs_init_block_rsv+0x51/0x60 [btrfs]
> btrfs_finish_one_ordered+0x3ea/0x840 [btrfs]
> btrfs_work_helper+0x103/0x4b0 [btrfs]
> ? lock_release+0x177/0x2e0
> process_one_work+0x21a/0x590
> ? lock_is_held_type+0xd5/0x130
> worker_thread+0x1bf/0x3c0
> ? __pfx_worker_thread+0x10/0x10
> kthread+0xdd/0x110
> ? __pfx_kthread+0x10/0x10
> ret_from_fork+0x2d/0x50
> ? __pfx_kthread+0x10/0x10
> ret_from_fork_asm+0x1a/0x30
> </TASK>
> Started fstests-check.scope - [systemd-run] /usr/bin/bash -c "exit 77".
> fstests-check.scope: Deactivated successfully.
>
> Signed-off-by: Swarna Prabhu <s.prabhu@xxxxxxxxxxx>
Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Luis
