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>
---
tests/generic/750 | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/tests/generic/750 b/tests/generic/750
index a0828b50..abce6a59 100755
--- a/tests/generic/750
+++ b/tests/generic/750
@@ -26,11 +26,13 @@ _cleanup()
_require_scratch
_require_vm_compaction
-# We still deadlock with this test on v6.10-rc2, we need more work.
-# but the below makes things better.
_fixed_by_git_commit kernel d99e3140a4d3 \
"mm: turn folio_test_hugetlb into a PageType"
+#merged on v6.11-rc4
+_fixed_by_git_commit kernel 2e6506e1c4ee \
+ "mm/migrate: fix deadlock in migrate_pages_batch() on large folios"
+
echo "Silence is golden"
_scratch_mkfs > $seqres.full 2>&1
--
2.47.2
