Re: [PATCH 2/8] xfs: use deferred frees for btree block freeing

Darrick J. Wong
2023-06-28T17:46:30Z

On Wed, Jun 28, 2023 at 08:44:06AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Btrees that aren't freespace management trees use the normal extent
> allocation and freeing routines for their blocks. Hence when a btree
> block is freed, a direct call to xfs_free_extent() is made and the
> extent is immediately freed. This puts the entire free space
> management btrees under this path, so we are stacking btrees on
> btrees in the call stack. The inobt, finobt and refcount btrees
> all do this.
>
> However, the bmap btree does not do this - it calls
> xfs_free_extent_later() to defer the extent free operation via an
> XEFI and hence it gets processed in deferred operation processing
> during the commit of the primary transaction (i.e. via intent
> chaining).
>
> We need to change xfs_free_extent() to behave in a non-blocking
> manner so that we can avoid deadlocks with busy extents near ENOSPC
> in transactions that free multiple extents. Inserting or removing a
> record from a btree can cause a multi-level tree merge operation and
> that will free multiple blocks from the btree in a single
> transaction. i.e. we can call xfs_free_extent() multiple times, and
> hence the btree manipulation transaction is vulnerable to this busy
> extent deadlock vector.
>
> To fix this, convert all the remaining callers of xfs_free_extent()
> to use xfs_free_extent_later() to queue XEFIs and hence defer
> processing of the extent frees to a context that can be safely
> restarted if a deadlock condition is detected.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/libxfs/xfs_ag.c | 2 +-
> fs/xfs/libxfs/xfs_alloc.c | 4 ++++
> fs/xfs/libxfs/xfs_alloc.h | 8 +++++---
> fs/xfs/libxfs/xfs_bmap.c | 8 +++++---
> fs/xfs/libxfs/xfs_bmap_btree.c | 3 ++-
> fs/xfs/libxfs/xfs_ialloc.c | 8 ++++----
> fs/xfs/libxfs/xfs_ialloc_btree.c | 3 +--
> fs/xfs/libxfs/xfs_refcount.c | 9 ++++++---
> fs/xfs/libxfs/xfs_refcount_btree.c | 8 +-------
> fs/xfs/xfs_extfree_item.c | 3 ++-
> fs/xfs/xfs_reflink.c | 3 ++-
> 11 files changed, 33 insertions(+), 26 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index ee84835ebc66..e9cc481b4ddf 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -985,7 +985,7 @@ xfs_ag_shrink_space(
> goto resv_err;
>
> err2 = __xfs_free_extent_later(*tpp, args.fsbno, delta, NULL,
> - true);
> + XFS_AG_RESV_NONE, true);
> if (err2)
> goto resv_err;
>
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index c20fe99405d8..cc3f7b905ea1 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2449,6 +2449,7 @@ xfs_defer_agfl_block(
> xefi->xefi_startblock = XFS_AGB_TO_FSB(mp, agno, agbno);
> xefi->xefi_blockcount = 1;
> xefi->xefi_owner = oinfo->oi_owner;
> + xefi->xefi_type = XFS_AG_RESV_AGFL;
> if (XFS_IS_CORRUPT(mp, !xfs_verify_fsbno(mp, xefi->xefi_startblock)))
> return -EFSCORRUPTED;
> @@ -2470,6 +2471,7 @@ __xfs_free_extent_later(
> xfs_fsblock_t bno,
> xfs_filblks_t len,
> const struct xfs_owner_info *oinfo,
> + enum xfs_ag_resv_type type,
> bool skip_discard)
> {
> struct xfs_extent_free_item *xefi;
> @@ -2490,6 +2492,7 @@ __xfs_free_extent_later(
> ASSERT(agbno + len <= mp->m_sb.sb_agblocks);
> #endif
> ASSERT(xfs_extfree_item_cache != NULL);
> + ASSERT(type != XFS_AG_RESV_AGFL);
>
> if (XFS_IS_CORRUPT(mp, !xfs_verify_fsbext(mp, bno, len)))
> return -EFSCORRUPTED;
> @@ -2498,6 +2501,7 @@ __xfs_free_extent_later(
> GFP_KERNEL | __GFP_NOFAIL);
> xefi->xefi_startblock = bno;
> xefi->xefi_blockcount = (xfs_extlen_t)len;
> + xefi->xefi_type = type;
> if (skip_discard)
> xefi->xefi_flags |= XFS_EFI_SKIP_DISCARD;
> if (oinfo) {
> diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
> index 85ac470be0da..121faf1e11ad 100644
> --- a/fs/xfs/libxfs/xfs_alloc.h
> +++ b/fs/xfs/libxfs/xfs_alloc.h
> @@ -232,7 +232,7 @@ xfs_buf_to_agfl_bno(
>
> int __xfs_free_extent_later(struct xfs_trans *tp, xfs_fsblock_t bno,
> xfs_filblks_t len, const struct xfs_owner_info *oinfo,
> - bool skip_discard);
> + enum xfs_ag_resv_type type, bool skip_discard);
>
> /*
> * List of extents to be free "later".
> @@ -245,6 +245,7 @@ struct xfs_extent_free_item {
> xfs_extlen_t xefi_blockcount;/* number of blocks in extent */
> struct xfs_perag *xefi_pag;
> unsigned int xefi_flags;

/me is barely back from vacation, starting to process the ~1100 emails
by taking care of the obvious bugfixes first...

> + enum xfs_ag_resv_type xefi_type;

I got confused by 'xefi_type' until I remembered that
XFS_DEFER_OPS_TYPE_AGFL_FREE / XFS_DEFER_OPS_TYPE_FREE are stuffed in
the xfs_defer_pending structure, not the xefi itself.

Could this field be named xefi_agresv instead?

The rest of the logic in this patch looks correct and makes things
easier for the rt modernization patches, so I'll say

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

and change the name on commit, if that's ok?

--D

> };
>
> void xfs_extent_free_get_group(struct xfs_mount *mp,
> @@ -259,9 +260,10 @@ xfs_free_extent_later(
> struct xfs_trans *tp,
> xfs_fsblock_t bno,
> xfs_filblks_t len,
> - const struct xfs_owner_info *oinfo)
> + const struct xfs_owner_info *oinfo,
> + enum xfs_ag_resv_type type)
> {
> - return __xfs_free_extent_later(tp, bno, len, oinfo, false);
> + return __xfs_free_extent_later(tp, bno, len, oinfo, type, false);
> }
>
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index fef35696adb7..30c931b38853 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -574,7 +574,8 @@ xfs_bmap_btree_to_extents(
> return error;
>
> xfs_rmap_ino_bmbt_owner(&oinfo, ip->i_ino, whichfork);
> - error = xfs_free_extent_later(cur->bc_tp, cbno, 1, &oinfo);
> + error = xfs_free_extent_later(cur->bc_tp, cbno, 1, &oinfo,
> + XFS_AG_RESV_NONE);
> if (error)
> return error;
>
> @@ -5236,8 +5237,9 @@ xfs_bmap_del_extent_real(
> } else {
> error = __xfs_free_extent_later(tp, del->br_startblock,
> del->br_blockcount, NULL,
> - (bflags & XFS_BMAPI_NODISCARD) ||
> - del->br_state == XFS_EXT_UNWRITTEN);
> + XFS_AG_RESV_NONE,
> + ((bflags & XFS_BMAPI_NODISCARD) ||
> + del->br_state == XFS_EXT_UNWRITTEN));
> if (error)
> goto done;
> }
> diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
> index 36564ae3084f..bf3f1b36fdd2 100644
> --- a/fs/xfs/libxfs/xfs_bmap_btree.c
> +++ b/fs/xfs/libxfs/xfs_bmap_btree.c
> @@ -271,7 +271,8 @@ xfs_bmbt_free_block(
> int error;
>
> xfs_rmap_ino_bmbt_owner(&oinfo, ip->i_ino, cur->bc_ino.whichfork);
> - error = xfs_free_extent_later(cur->bc_tp, fsbno, 1, &oinfo);
> + error = xfs_free_extent_later(cur->bc_tp, fsbno, 1, &oinfo,
> + XFS_AG_RESV_NONE);
> if (error)
> return error;
>
> diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> index 34600f94c2f4..1e5fafbc0cdb 100644
> --- a/fs/xfs/libxfs/xfs_ialloc.c
> +++ b/fs/xfs/libxfs/xfs_ialloc.c
> @@ -1853,8 +1853,8 @@ xfs_difree_inode_chunk(
> /* not sparse, calculate extent info directly */
> return xfs_free_extent_later(tp,
> XFS_AGB_TO_FSB(mp, agno, sagbno),
> - M_IGEO(mp)->ialloc_blks,
> - &XFS_RMAP_OINFO_INODES);
> + M_IGEO(mp)->ialloc_blks, &XFS_RMAP_OINFO_INODES,
> + XFS_AG_RESV_NONE);
> }
>
> /* holemask is only 16-bits (fits in an unsigned long) */
> @@ -1899,8 +1899,8 @@ xfs_difree_inode_chunk(
> ASSERT(agbno % mp->m_sb.sb_spino_align == 0);
> ASSERT(contigblk % mp->m_sb.sb_spino_align == 0);
> error = xfs_free_extent_later(tp,
> - XFS_AGB_TO_FSB(mp, agno, agbno),
> - contigblk, &XFS_RMAP_OINFO_INODES);
> + XFS_AGB_TO_FSB(mp, agno, agbno), contigblk,
> + &XFS_RMAP_OINFO_INODES, XFS_AG_RESV_NONE);
> if (error)
> return error;
>
> diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
> index 5a945ae21b5d..9258f01c0015 100644
> --- a/fs/xfs/libxfs/xfs_ialloc_btree.c
> +++ b/fs/xfs/libxfs/xfs_ialloc_btree.c
> @@ -160,8 +160,7 @@ __xfs_inobt_free_block(
>
> xfs_inobt_mod_blockcount(cur, -1);
> fsbno = XFS_DADDR_TO_FSB(cur->bc_mp, xfs_buf_daddr(bp));
> - return xfs_free_extent(cur->bc_tp, cur->bc_ag.pag,
> - XFS_FSB_TO_AGBNO(cur->bc_mp, fsbno), 1,
> + return xfs_free_extent_later(cur->bc_tp, fsbno, 1,
> &XFS_RMAP_OINFO_INOBT, resv);
> }
>
> diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c
> index b6e21433925c..70ab113c9cea 100644
> --- a/fs/xfs/libxfs/xfs_refcount.c
> +++ b/fs/xfs/libxfs/xfs_refcount.c
> @@ -1152,7 +1152,8 @@ xfs_refcount_adjust_extents(
> cur->bc_ag.pag->pag_agno,
> tmp.rc_startblock);
> error = xfs_free_extent_later(cur->bc_tp, fsbno,
> - tmp.rc_blockcount, NULL);
> + tmp.rc_blockcount, NULL,
> + XFS_AG_RESV_NONE);
> if (error)
> goto out_error;
> }
> @@ -1213,7 +1214,8 @@ xfs_refcount_adjust_extents(
> cur->bc_ag.pag->pag_agno,
> ext.rc_startblock);
> error = xfs_free_extent_later(cur->bc_tp, fsbno,
> - ext.rc_blockcount, NULL);
> + ext.rc_blockcount, NULL,
> + XFS_AG_RESV_NONE);
> if (error)
> goto out_error;
> }
> @@ -1981,7 +1983,8 @@ xfs_refcount_recover_cow_leftovers(
>
> /* Free the block. */
> error = xfs_free_extent_later(tp, fsb,
> - rr->rr_rrec.rc_blockcount, NULL);
> + rr->rr_rrec.rc_blockcount, NULL,
> + XFS_AG_RESV_NONE);
> if (error)
> goto out_trans;
>
> diff --git a/fs/xfs/libxfs/xfs_refcount_btree.c b/fs/xfs/libxfs/xfs_refcount_btree.c
> index d4afc5f4e6a5..5c3987d8dc24 100644
> --- a/fs/xfs/libxfs/xfs_refcount_btree.c
> +++ b/fs/xfs/libxfs/xfs_refcount_btree.c
> @@ -106,19 +106,13 @@ xfs_refcountbt_free_block(
> struct xfs_buf *agbp = cur->bc_ag.agbp;
> struct xfs_agf *agf = agbp->b_addr;
> xfs_fsblock_t fsbno = XFS_DADDR_TO_FSB(mp, xfs_buf_daddr(bp));
> - int error;
>
> trace_xfs_refcountbt_free_block(cur->bc_mp, cur->bc_ag.pag->pag_agno,
> XFS_FSB_TO_AGBNO(cur->bc_mp, fsbno), 1);
> be32_add_cpu(&agf->agf_refcount_blocks, -1);
> xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_REFCOUNT_BLOCKS);
> - error = xfs_free_extent(cur->bc_tp, cur->bc_ag.pag,
> - XFS_FSB_TO_AGBNO(cur->bc_mp, fsbno), 1,
> + return xfs_free_extent_later(cur->bc_tp, fsbno, 1,
> &XFS_RMAP_OINFO_REFC, XFS_AG_RESV_METADATA);
> - if (error)
> - return error;
> -
> - return error;
> }
>
> STATIC int
> diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
> index f9e36b810663..79e65bb6b0a2 100644
> --- a/fs/xfs/xfs_extfree_item.c
> +++ b/fs/xfs/xfs_extfree_item.c
> @@ -365,7 +365,7 @@ xfs_trans_free_extent(
> agbno, xefi->xefi_blockcount);
>
> error = __xfs_free_extent(tp, xefi->xefi_pag, agbno,
> - xefi->xefi_blockcount, &oinfo, XFS_AG_RESV_NONE,
> + xefi->xefi_blockcount, &oinfo, xefi->xefi_type,
> xefi->xefi_flags & XFS_EFI_SKIP_DISCARD);
>
> /*
> @@ -644,6 +644,7 @@ xfs_efi_item_recover(
> for (i = 0; i < efip->efi_format.efi_nextents; i++) {
> struct xfs_extent_free_item fake = {
> .xefi_owner = XFS_RMAP_OWN_UNKNOWN,
> + .xefi_type = XFS_AG_RESV_NONE,
> };
> struct xfs_extent *extp;
>
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index abcc559f3c64..eb9102453aff 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -617,7 +617,8 @@ xfs_reflink_cancel_cow_blocks(
> del.br_blockcount);
>
> error = xfs_free_extent_later(*tpp, del.br_startblock,
> - del.br_blockcount, NULL);
> + del.br_blockcount, NULL,
> + XFS_AG_RESV_NONE);
> if (error)
> break;
>
> --
> 2.40.1
>