Re: [PATCH][v2] RDMA/core: Prevent soft lockup during large user memory region cleanup

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Nov 13, 2025 at 05:53:17PM +0800, lirongqing wrote:
> From: Li RongQing <lirongqing@baidu.com>
> 
> When a process exits with numerous large, pinned memory regions consisting
> of 4KB pages, the cleanup of the memory region through __ib_umem_release()
> may cause soft lockups. This is because unpin_user_page_range_dirty_lock()
> is called in a tight loop for unpin and releasing page without yielding the
> CPU.
> 
>  watchdog: BUG: soft lockup - CPU#44 stuck for 26s! [python3:73464]
>  Kernel panic - not syncing: softlockup: hung tasks
>  CPU: 44 PID: 73464 Comm: python3 Tainted: G           OEL
> 
>  asm_sysvec_apic_timer_interrupt+0x1b/0x20
>  RIP: 0010:free_unref_page+0xff/0x190
> 
>   ? free_unref_page+0xe3/0x190
>   __put_page+0x77/0xe0
>   put_compound_head+0xed/0x100
>   unpin_user_page_range_dirty_lock+0xb2/0x180
>   __ib_umem_release+0x57/0xb0 [ib_core]
>   ib_umem_release+0x3f/0xd0 [ib_core]
>   mlx5_ib_dereg_mr+0x2e9/0x440 [mlx5_ib]
>   ib_dereg_mr_user+0x43/0xb0 [ib_core]
>   uverbs_free_mr+0x15/0x20 [ib_uverbs]
>   destroy_hw_idr_uobject+0x21/0x60 [ib_uverbs]
>   uverbs_destroy_uobject+0x38/0x1b0 [ib_uverbs]
>   __uverbs_cleanup_ufile+0xd1/0x150 [ib_uverbs]
>   uverbs_destroy_ufile_hw+0x3f/0x100 [ib_uverbs]
>   ib_uverbs_close+0x1f/0xb0 [ib_uverbs]
>   __fput+0x9c/0x280
>   ____fput+0xe/0x20
>   task_work_run+0x6a/0xb0
>   do_exit+0x217/0x3c0
>   do_group_exit+0x3b/0xb0
>   get_signal+0x150/0x900
>   arch_do_signal_or_restart+0xde/0x100
>   exit_to_user_mode_loop+0xc4/0x160
>   exit_to_user_mode_prepare+0xa0/0xb0
>   syscall_exit_to_user_mode+0x27/0x50
>   do_syscall_64+0x63/0xb0
> 
> Fix soft lockup issues by incorporating cond_resched() calls within
> __ib_umem_release(), and this SG entries are typically grouped in 2MB
> chunks on x86_64, adding cond_resched() should has minimal performance
> impact.

This is not true, I think this should have been more careful to only
resched after larger groupings.. How much slower did you make normal
4k unpins??

Jason