Re: [PATCH 2/6] XFS: Don't directly reference m_perag in allocation code

[Dave Chinner <david@fromorbit.com>]

On Tue, Dec 15, 2009 at 05:11:13PM +1100, Dave Chinner wrote:
> Start abstracting the perag references so that the indexing of the
> structures is not directly coded into all the places that uses the
> perag structures. This will allow us to separate the use of the
> perag structure and the way it is indexed and hence avoid the known
> deadlocks related to growing a busy filesystem.
> 
> Signed-off-by: Dave Chinner <david@fromorbit.com>

I screwed up the rebase so this patch is missing a xfs_perag_put()
call in xfs_alloc_get_freelist(), so will assert fail on unmount in
test 042. Corrected patch below.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

XFS: Don't directly reference m_perag in allocation code

Start abstracting the perag references so that the indexing of the
structures is not directly coded into all the places that uses the
perag structures. This will allow us to separate the use of the
perag structure and the way it is indexed and hence avoid the known
deadlocks related to growing a busy filesystem.

Signed-off-by: Dave Chinner <david@fromorbit.com>
---
 fs/xfs/xfs_alloc.c       |   82 ++++++++++++++++++++++++++--------------------
 fs/xfs/xfs_alloc_btree.c |    9 ++++-
 2 files changed, 53 insertions(+), 38 deletions(-)

diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index a1c65fc..d39ee2d 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -1662,11 +1662,13 @@ xfs_free_ag_extent(
 		xfs_agf_t	*agf;
 		xfs_perag_t	*pag;		/* per allocation group data */
 
+		pag = xfs_perag_get(mp, agno);
+		pag->pagf_freeblks += len;
+		xfs_perag_put(pag);
+
 		agf = XFS_BUF_TO_AGF(agbp);
-		pag = &mp->m_perag[agno];
 		be32_add_cpu(&agf->agf_freeblks, len);
 		xfs_trans_agblocks_delta(tp, len);
-		pag->pagf_freeblks += len;
 		XFS_WANT_CORRUPTED_GOTO(
 			be32_to_cpu(agf->agf_freeblks) <=
 			be32_to_cpu(agf->agf_length),
@@ -1969,10 +1971,12 @@ xfs_alloc_get_freelist(
 	xfs_trans_brelse(tp, agflbp);
 	if (be32_to_cpu(agf->agf_flfirst) == XFS_AGFL_SIZE(mp))
 		agf->agf_flfirst = 0;
-	pag = &mp->m_perag[be32_to_cpu(agf->agf_seqno)];
+
+	pag = xfs_perag_get(mp, be32_to_cpu(agf->agf_seqno));
 	be32_add_cpu(&agf->agf_flcount, -1);
 	xfs_trans_agflist_delta(tp, -1);
 	pag->pagf_flcount--;
+	xfs_perag_put(pag);
 
 	logflags = XFS_AGF_FLFIRST | XFS_AGF_FLCOUNT;
 	if (btreeblk) {
@@ -2078,7 +2082,8 @@ xfs_alloc_put_freelist(
 	be32_add_cpu(&agf->agf_fllast, 1);
 	if (be32_to_cpu(agf->agf_fllast) == XFS_AGFL_SIZE(mp))
 		agf->agf_fllast = 0;
-	pag = &mp->m_perag[be32_to_cpu(agf->agf_seqno)];
+
+	pag = xfs_perag_get(mp, be32_to_cpu(agf->agf_seqno));
 	be32_add_cpu(&agf->agf_flcount, 1);
 	xfs_trans_agflist_delta(tp, 1);
 	pag->pagf_flcount++;
@@ -2089,6 +2094,7 @@ xfs_alloc_put_freelist(
 		pag->pagf_btreeblks--;
 		logflags |= XFS_AGF_BTREEBLKS;
 	}
+	xfs_perag_put(pag);
 
 	xfs_alloc_log_agf(tp, agbp, logflags);
 
@@ -2152,7 +2158,6 @@ xfs_read_agf(
 		xfs_trans_brelse(tp, *bpp);
 		return XFS_ERROR(EFSCORRUPTED);
 	}
-
 	XFS_BUF_SET_VTYPE_REF(*bpp, B_FS_AGF, XFS_AGF_REF);
 	return 0;
 }
@@ -2184,7 +2189,7 @@ xfs_alloc_read_agf(
 	ASSERT(!XFS_BUF_GETERROR(*bpp));
 
 	agf = XFS_BUF_TO_AGF(*bpp);
-	pag = &mp->m_perag[agno];
+	pag = xfs_perag_get(mp, agno);
 	if (!pag->pagf_init) {
 		pag->pagf_freeblks = be32_to_cpu(agf->agf_freeblks);
 		pag->pagf_btreeblks = be32_to_cpu(agf->agf_btreeblks);
@@ -2211,6 +2216,7 @@ xfs_alloc_read_agf(
 		       be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNTi]));
 	}
 #endif
+	xfs_perag_put(pag);
 	return 0;
 }
 
@@ -2271,7 +2277,7 @@ xfs_alloc_vextent(
 		 */
 		args->agno = XFS_FSB_TO_AGNO(mp, args->fsbno);
 		down_read(&mp->m_peraglock);
-		args->pag = &mp->m_perag[args->agno];
+		args->pag = xfs_perag_get(mp, args->agno);
 		args->minleft = 0;
 		error = xfs_alloc_fix_freelist(args, 0);
 		args->minleft = minleft;
@@ -2341,7 +2347,7 @@ xfs_alloc_vextent(
 		 */
 		down_read(&mp->m_peraglock);
 		for (;;) {
-			args->pag = &mp->m_perag[args->agno];
+			args->pag = xfs_perag_get(mp, args->agno);
 			if (no_min) args->minleft = 0;
 			error = xfs_alloc_fix_freelist(args, flags);
 			args->minleft = minleft;
@@ -2400,6 +2406,7 @@ xfs_alloc_vextent(
 					}
 				}
 			}
+			xfs_perag_put(args->pag);
 		}
 		up_read(&mp->m_peraglock);
 		if (bump_rotor || (type == XFS_ALLOCTYPE_ANY_AG)) {
@@ -2427,8 +2434,10 @@ xfs_alloc_vextent(
 			args->len);
 #endif
 	}
+	xfs_perag_put(args->pag);
 	return 0;
 error0:
+	xfs_perag_put(args->pag);
 	up_read(&mp->m_peraglock);
 	return error;
 }
@@ -2455,7 +2464,7 @@ xfs_free_extent(
 	ASSERT(args.agno < args.mp->m_sb.sb_agcount);
 	args.agbno = XFS_FSB_TO_AGBNO(args.mp, bno);
 	down_read(&args.mp->m_peraglock);
-	args.pag = &args.mp->m_perag[args.agno];
+	args.pag = xfs_perag_get(args.mp, args.agno);
 	if ((error = xfs_alloc_fix_freelist(&args, XFS_ALLOC_FLAG_FREEING)))
 		goto error0;
 #ifdef DEBUG
@@ -2465,6 +2474,7 @@ xfs_free_extent(
 #endif
 	error = xfs_free_ag_extent(tp, args.agbp, args.agno, args.agbno, len, 0);
 error0:
+	xfs_perag_put(args.pag);
 	up_read(&args.mp->m_peraglock);
 	return error;
 }
@@ -2486,15 +2496,15 @@ xfs_alloc_mark_busy(xfs_trans_t *tp,
 		    xfs_agblock_t bno,
 		    xfs_extlen_t len)
 {
-	xfs_mount_t		*mp;
 	xfs_perag_busy_t	*bsy;
+	struct xfs_perag	*pag;
 	int			n;
 
-	mp = tp->t_mountp;
-	spin_lock(&mp->m_perag[agno].pagb_lock);
+	pag = xfs_perag_get(tp->t_mountp, agno);
+	spin_lock(&pag->pagb_lock);
 
 	/* search pagb_list for an open slot */
-	for (bsy = mp->m_perag[agno].pagb_list, n = 0;
+	for (bsy = pag->pagb_list, n = 0;
 	     n < XFS_PAGB_NUM_SLOTS;
 	     bsy++, n++) {
 		if (bsy->busy_tp == NULL) {
@@ -2502,11 +2512,11 @@ xfs_alloc_mark_busy(xfs_trans_t *tp,
 		}
 	}
 
-	trace_xfs_alloc_busy(mp, agno, bno, len, n);
+	trace_xfs_alloc_busy(tp->t_mountp, agno, bno, len, n);
 
 	if (n < XFS_PAGB_NUM_SLOTS) {
-		bsy = &mp->m_perag[agno].pagb_list[n];
-		mp->m_perag[agno].pagb_count++;
+		bsy = &pag->pagb_list[n];
+		pag->pagb_count++;
 		bsy->busy_start = bno;
 		bsy->busy_length = len;
 		bsy->busy_tp = tp;
@@ -2521,7 +2531,8 @@ xfs_alloc_mark_busy(xfs_trans_t *tp,
 		xfs_trans_set_sync(tp);
 	}
 
-	spin_unlock(&mp->m_perag[agno].pagb_lock);
+	spin_unlock(&pag->pagb_lock);
+	xfs_perag_put(pag);
 }
 
 void
@@ -2529,24 +2540,23 @@ xfs_alloc_clear_busy(xfs_trans_t *tp,
 		     xfs_agnumber_t agno,
 		     int idx)
 {
-	xfs_mount_t		*mp;
+	struct xfs_perag	*pag;
 	xfs_perag_busy_t	*list;
 
-	mp = tp->t_mountp;
-
-	spin_lock(&mp->m_perag[agno].pagb_lock);
-	list = mp->m_perag[agno].pagb_list;
-
 	ASSERT(idx < XFS_PAGB_NUM_SLOTS);
+	pag = xfs_perag_get(tp->t_mountp, agno);
+	spin_lock(&pag->pagb_lock);
+	list = pag->pagb_list;
 
-	trace_xfs_alloc_unbusy(mp, agno, idx, list[idx].busy_tp == tp);
+	trace_xfs_alloc_unbusy(tp->t_mountp, agno, idx, list[idx].busy_tp == tp);
 
 	if (list[idx].busy_tp == tp) {
 		list[idx].busy_tp = NULL;
-		mp->m_perag[agno].pagb_count--;
+		pag->pagb_count--;
 	}
 
-	spin_unlock(&mp->m_perag[agno].pagb_lock);
+	spin_unlock(&pag->pagb_lock);
+	xfs_perag_put(pag);
 }
 
 
@@ -2560,21 +2570,20 @@ xfs_alloc_search_busy(xfs_trans_t *tp,
 		    xfs_agblock_t bno,
 		    xfs_extlen_t len)
 {
-	xfs_mount_t		*mp;
+	struct xfs_perag	*pag;
 	xfs_perag_busy_t	*bsy;
 	xfs_agblock_t		uend, bend;
 	xfs_lsn_t		lsn;
 	int			cnt;
 
-	mp = tp->t_mountp;
-
-	spin_lock(&mp->m_perag[agno].pagb_lock);
-	cnt = mp->m_perag[agno].pagb_count;
+	pag = xfs_perag_get(tp->t_mountp, agno);
+	spin_lock(&pag->pagb_lock);
+	cnt = pag->pagb_count;
 
 	uend = bno + len - 1;
 
 	/* search pagb_list for this slot, skipping open slots */
-	for (bsy = mp->m_perag[agno].pagb_list; cnt; bsy++) {
+	for (bsy = pag->pagb_list; cnt; bsy++) {
 
 		/*
 		 * (start1,length1) within (start2, length2)
@@ -2589,7 +2598,7 @@ xfs_alloc_search_busy(xfs_trans_t *tp,
 		}
 	}
 
-	trace_xfs_alloc_busysearch(mp, agno, bno, len, !!cnt);
+	trace_xfs_alloc_busysearch(tp->t_mountp, agno, bno, len, !!cnt);
 
 	/*
 	 * If a block was found, force the log through the LSN of the
@@ -2597,9 +2606,10 @@ xfs_alloc_search_busy(xfs_trans_t *tp,
 	 */
 	if (cnt) {
 		lsn = bsy->busy_tp->t_commit_lsn;
-		spin_unlock(&mp->m_perag[agno].pagb_lock);
-		xfs_log_force(mp, lsn, XFS_LOG_FORCE|XFS_LOG_SYNC);
+		spin_unlock(&pag->pagb_lock);
+		xfs_log_force(tp->t_mountp, lsn, XFS_LOG_FORCE|XFS_LOG_SYNC);
 	} else {
-		spin_unlock(&mp->m_perag[agno].pagb_lock);
+		spin_unlock(&pag->pagb_lock);
 	}
+	xfs_perag_put(pag);
 }
diff --git a/fs/xfs/xfs_alloc_btree.c b/fs/xfs/xfs_alloc_btree.c
index adbd914..b726e10 100644
--- a/fs/xfs/xfs_alloc_btree.c
+++ b/fs/xfs/xfs_alloc_btree.c
@@ -61,12 +61,14 @@ xfs_allocbt_set_root(
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(agbp);
 	xfs_agnumber_t		seqno = be32_to_cpu(agf->agf_seqno);
 	int			btnum = cur->bc_btnum;
+	struct xfs_perag	*pag = xfs_perag_get(cur->bc_mp, seqno);
 
 	ASSERT(ptr->s != 0);
 
 	agf->agf_roots[btnum] = ptr->s;
 	be32_add_cpu(&agf->agf_levels[btnum], inc);
-	cur->bc_mp->m_perag[seqno].pagf_levels[btnum] += inc;
+	pag->pagf_levels[btnum] += inc;
+	xfs_perag_put(pag);
 
 	xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_ROOTS | XFS_AGF_LEVELS);
 }
@@ -150,6 +152,7 @@ xfs_allocbt_update_lastrec(
 {
 	struct xfs_agf		*agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
 	xfs_agnumber_t		seqno = be32_to_cpu(agf->agf_seqno);
+	struct xfs_perag	*pag;
 	__be32			len;
 	int			numrecs;
 
@@ -193,7 +196,9 @@ xfs_allocbt_update_lastrec(
 	}
 
 	agf->agf_longest = len;
-	cur->bc_mp->m_perag[seqno].pagf_longest = be32_to_cpu(len);
+	pag = xfs_perag_get(cur->bc_mp, seqno);
+	pag->pagf_longest = be32_to_cpu(len);
+	xfs_perag_put(pag);
 	xfs_alloc_log_agf(cur->bc_tp, cur->bc_private.a.agbp, XFS_AGF_LONGEST);
 }
 

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