Re: [PATCH] iomap: Address soft lockup in iomap_finish_ioend()

[Dave Chinner <david@fromorbit.com>]

On Tue, Jan 11, 2022 at 10:37:46AM +1100, Dave Chinner wrote:
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index c8c15c3c3147..82515d1ad4e0 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -136,7 +136,20 @@ xfs_end_ioend(
>  	memalloc_nofs_restore(nofs_flag);
>  }
>  
> -/* Finish all pending io completions. */
> +/*
> + * Finish all pending IO completions that require transactional modifications.
> + *
> + * We try to merge physical and logically contiguous ioends before completion to
> + * minimise the number of transactions we need to perform during IO completion.
> + * Both unwritten extent conversion and COW remapping need to iterate and modify
> + * one physical extent at a time, so we gain nothing by merging physically
> + * discontiguous extents here.
> + *
> + * The ioend chain length that we can be processing here is largely unbound in
> + * length and we may have to perform significant amounts of work on each ioend
> + * to complete it. Hence we have to be careful about holding the CPU for too
> + * long in this loop.
> + */
>  void
>  xfs_end_io(
>  	struct work_struct	*work)
> @@ -147,6 +160,7 @@ xfs_end_io(
>  	struct list_head	tmp;
>  	unsigned long		flags;
>  
> +	msleep(5000);
>  	spin_lock_irqsave(&ip->i_ioend_lock, flags);
>  	list_replace_init(&ip->i_ioend_list, &tmp);
>  	spin_unlock_irqrestore(&ip->i_ioend_lock, flags);

You might want to comment that 5s completion delay out before you
run the patch, Trond...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com