Re: [PATCHv4 1/1] xfs: Add cond_resched to block unmap range and reflink remap path

[Disha Goel <disgoel@linux.ibm.com>]

On 07/05/24 3:06 pm, Ritesh Harjani (IBM) wrote:

> An async dio write to a sparse file can generate a lot of extents
> and when we unlink this file (using rm), the kernel can be busy in umapping
> and freeing those extents as part of transaction processing.
>
> Similarly xfs reflink remapping path can also iterate over a million
> extent entries in xfs_reflink_remap_blocks().
>
> Since we can busy loop in these two functions, so let's add cond_resched()
> to avoid softlockup messages like these.
>
> watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:82435]
> CPU: 1 PID: 82435 Comm: kworker/1:0 Tainted: G S  L   6.9.0-rc5-0-default #1
> Workqueue: xfs-inodegc/sda2 xfs_inodegc_worker
> NIP [c000000000beea10] xfs_extent_busy_trim+0x100/0x290
> LR [c000000000bee958] xfs_extent_busy_trim+0x48/0x290
> Call Trace:
>    xfs_alloc_get_rec+0x54/0x1b0 (unreliable)
>    xfs_alloc_compute_aligned+0x5c/0x144
>    xfs_alloc_ag_vextent_size+0x238/0x8d4
>    xfs_alloc_fix_freelist+0x540/0x694
>    xfs_free_extent_fix_freelist+0x84/0xe0
>    __xfs_free_extent+0x74/0x1ec
>    xfs_extent_free_finish_item+0xcc/0x214
>    xfs_defer_finish_one+0x194/0x388
>    xfs_defer_finish_noroll+0x1b4/0x5c8
>    xfs_defer_finish+0x2c/0xc4
>    xfs_bunmapi_range+0xa4/0x100
>    xfs_itruncate_extents_flags+0x1b8/0x2f4
>    xfs_inactive_truncate+0xe0/0x124
>    xfs_inactive+0x30c/0x3e0
>    xfs_inodegc_worker+0x140/0x234
>    process_scheduled_works+0x240/0x57c
>    worker_thread+0x198/0x468
>    kthread+0x138/0x140
>    start_kernel_thread+0x14/0x18
>
> run fstests generic/175 at 2024-02-02 04:40:21
> [   C17] watchdog: BUG: soft lockup - CPU#17 stuck for 23s! [xfs_io:7679]
>   watchdog: BUG: soft lockup - CPU#17 stuck for 23s! [xfs_io:7679]
>   CPU: 17 PID: 7679 Comm: xfs_io Kdump: loaded Tainted: G X 6.4.0
>   NIP [c008000005e3ec94] xfs_rmapbt_diff_two_keys+0x54/0xe0 [xfs]
>   LR [c008000005e08798] xfs_btree_get_leaf_keys+0x110/0x1e0 [xfs]
>   Call Trace:
>    0xc000000014107c00 (unreliable)
>    __xfs_btree_updkeys+0x8c/0x2c0 [xfs]
>    xfs_btree_update_keys+0x150/0x170 [xfs]
>    xfs_btree_lshift+0x534/0x660 [xfs]
>    xfs_btree_make_block_unfull+0x19c/0x240 [xfs]
>    xfs_btree_insrec+0x4e4/0x630 [xfs]
>    xfs_btree_insert+0x104/0x2d0 [xfs]
>    xfs_rmap_insert+0xc4/0x260 [xfs]
>    xfs_rmap_map_shared+0x228/0x630 [xfs]
>    xfs_rmap_finish_one+0x2d4/0x350 [xfs]
>    xfs_rmap_update_finish_item+0x44/0xc0 [xfs]
>    xfs_defer_finish_noroll+0x2e4/0x740 [xfs]
>    __xfs_trans_commit+0x1f4/0x400 [xfs]
>    xfs_reflink_remap_extent+0x2d8/0x650 [xfs]
>    xfs_reflink_remap_blocks+0x154/0x320 [xfs]
>    xfs_file_remap_range+0x138/0x3a0 [xfs]
>    do_clone_file_range+0x11c/0x2f0
>    vfs_clone_file_range+0x60/0x1c0
>    ioctl_file_clone+0x78/0x140
>    sys_ioctl+0x934/0x1270
>    system_call_exception+0x158/0x320
>    system_call_vectored_common+0x15c/0x2ec
>
> Cc: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Thanks for the fix patch. I have tested it on a power machine,
and it resolves the soft lockup issue.

Tested-by: Disha Goel<disgoel@linux.ibm.com>

> ---
>   fs/xfs/libxfs/xfs_bmap.c | 1 +
>   fs/xfs/xfs_reflink.c     | 1 +
>   2 files changed, 2 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 656c95a22f2e..44d5381bc66f 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -6354,6 +6354,7 @@ xfs_bunmapi_range(
>   		error = xfs_defer_finish(tpp);
>   		if (error)
>   			goto out;
> +		cond_resched();
>   	}
>   out:
>   	return error;
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 7da0e8f961d3..5f26a608bc09 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1417,6 +1417,7 @@ xfs_reflink_remap_blocks(
>   		destoff += imap.br_blockcount;
>   		len -= imap.br_blockcount;
>   		remapped_len += imap.br_blockcount;
> +		cond_resched();
>   	}
>
>   	if (error)
> --
> 2.44.0
>
>