Re: Hard and soft lockups with FIO and LTP runs on a large system

[Bharata B Rao <bharata@amd.com>]

Hi Yu Zhao,

Thanks for your patches. See below...

On 07-Jul-24 4:12 AM, Yu Zhao wrote:
> Hi Bharata,
> 
> On Wed, Jul 3, 2024 at 9:11 AM Bharata B Rao <bharata@amd.com> wrote:
>>
<snip>
>> 
>> Some experiments tried
>> ======================
>> 1) When MGLRU was enabled many soft lockups were observed, no hard
>> lockups were seen for 48 hours run. Below is once such soft lockup.
> 
> This is not really an MGLRU issue -- can you please try one of the
> attached patches? It (truncate.patch) should help with or without
> MGLRU.

With truncate.patch and default LRU scheme, a few hard lockups are seen.

First one is this:

watchdog: Watchdog detected hard LOCKUP on cpu 487
CPU: 487 PID: 11525 Comm: fio Not tainted 6.10.0-rc3 #27
RIP: 0010:native_queued_spin_lock_slowpath+0x81/0x300
Call Trace:
   <NMI>
   ? show_regs+0x69/0x80
   ? watchdog_hardlockup_check+0x1b4/0x3a0
<SNIP>
   ? native_queued_spin_lock_slowpath+0x81/0x300
   </NMI>
   <TASK>
   ? __pfx_folio_activate_fn+0x10/0x10
   _raw_spin_lock_irqsave+0x5b/0x70
   folio_lruvec_lock_irqsave+0x62/0x90
   folio_batch_move_lru+0x9d/0x160
   folio_activate+0x95/0xe0
   folio_mark_accessed+0x11f/0x160
   filemap_read+0x343/0x3d0
<SNIP>
   blkdev_read_iter+0x6f/0x140
   vfs_read+0x25b/0x340
   ksys_read+0x67/0xf0
   __x64_sys_read+0x19/0x20
   x64_sys_call+0x1771/0x20d0

This is the next one:

watchdog: Watchdog detected hard LOCKUP on cpu 219
CPU: 219 PID: 2584763 Comm: fs_racer_dir_cr Not tainted 6.10.0-rc3 #27
RIP: 0010:native_queued_spin_lock_slowpath+0x2b4/0x300
Call Trace:
   <NMI>
   ? show_regs+0x69/0x80
   ? watchdog_hardlockup_check+0x1b4/0x3a0
<SNIP>
   ? native_queued_spin_lock_slowpath+0x2b4/0x300
   </NMI>
   <TASK>
   _raw_spin_lock_irqsave+0x5b/0x70
   folio_lruvec_lock_irqsave+0x62/0x90
   __page_cache_release+0x89/0x2f0
   folios_put_refs+0x92/0x230
   __folio_batch_release+0x74/0x90
   truncate_inode_pages_range+0x16f/0x520
   truncate_pagecache+0x49/0x70
   ext4_setattr+0x326/0xaa0
   notify_change+0x353/0x500
   do_truncate+0x83/0xe0
   path_openat+0xd9e/0x1090
   do_filp_open+0xaa/0x150
   do_sys_openat2+0x9b/0xd0
   __x64_sys_openat+0x55/0x90
   x64_sys_call+0xe55/0x20d0
   do_syscall_64+0x7e/0x130
   entry_SYSCALL_64_after_hwframe+0x76/0x7e

When this happens, all-CPU backtrace shows a CPU being in 
isolate_lru_folios().

> 
>> kernel: watchdog: BUG: soft lockup - CPU#29 stuck for 11s! [fio:2701649]
>> kernel: CPU: 29 PID: 2701649 Comm: fio Tainted: G             L
>> 6.10.0-rc3-mglru-irqstrc #24
>> kernel: RIP: 0010:native_queued_spin_lock_slowpath+0x2b4/0x300
>> kernel: Call Trace:
>> kernel:  <IRQ>
>> kernel:  ? show_regs+0x69/0x80
>> kernel:  ? watchdog_timer_fn+0x223/0x2b0
>> kernel:  ? __pfx_watchdog_timer_fn+0x10/0x10
>> <SNIP>
>> kernel:  </IRQ>
>> kernel:  <TASK>
>> kernel:  ? asm_sysvec_apic_timer_interrupt+0x1b/0x20
>> kernel:  ? native_queued_spin_lock_slowpath+0x2b4/0x300
>> kernel:  _raw_spin_lock+0x38/0x50
>> kernel:  clear_shadow_entry+0x3d/0x100
>> kernel:  ? __pfx_workingset_update_node+0x10/0x10
>> kernel:  mapping_try_invalidate+0x117/0x1d0
>> kernel:  invalidate_mapping_pages+0x10/0x20
>> kernel:  invalidate_bdev+0x3c/0x50
>> kernel:  blkdev_common_ioctl+0x5f7/0xa90
>> kernel:  blkdev_ioctl+0x109/0x270
>> kernel:  x64_sys_call+0x1215/0x20d0
>> kernel:  do_syscall_64+0x7e/0x130
>>
>> This happens to be contending on inode i_lock spinlock.
>>
>> Below preemptirqsoff trace points to preemption being disabled for more
>> than 10s and the lock in picture is lruvec spinlock.
> 
> Also if you could try the other patch (mglru.patch) please. It should
> help reduce unnecessary rotations from deactivate_file_folio(), which
> in turn should reduce the contention on the LRU lock for MGLRU.

Currently testing is in progress with mglru.patch and MGLRU enabled. 
Will get back on the results.

Regards,
Bharata.