xfs: fix finding a last resort AG in xfs_filestream_pick_ag

When the main loop in xfs_filestream_pick_ag fails to find a suitable
AG it tries to just pick the online AG.  But the loop for that uses
args->pag as loop iterator while the later code expects pag to be
set.  Fix this by reusing the max_pag case for this last resort, and
also add a check for impossible case of no AG just to make sure that
the uninitialized pag doesn't even escape in theory.

Reported-by: [email protected]
Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: [email protected]
Fixes: f8f1ed1 ("xfs: return a referenced perag from filestreams allocator")
Cc: <[email protected]> # v6.3
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>

Author: Christoph Hellwig

fs/xfs/xfs_filestream.c

@@ -64,7 +64,7 @@ xfs_filestream_pick_ag(
 	struct xfs_perag	*pag;
 	struct xfs_perag	*max_pag = NULL;
 	xfs_extlen_t		minlen = *longest;
-	xfs_extlen_t		free = 0, minfree, maxfree = 0;
+	xfs_extlen_t		minfree, maxfree = 0;
 	xfs_agnumber_t		agno;
 	bool			first_pass = true;
 	int			err;
@@ -107,7 +107,6 @@ xfs_filestream_pick_ag(
 			     !(flags & XFS_PICK_USERDATA) ||
 			     (flags & XFS_PICK_LOWSPACE))) {
 				/* Break out, retaining the reference on the AG. */
-				free = pag->pagf_freeblks;
 				break;
 			}
 		}
@@ -150,23 +149,25 @@ xfs_filestream_pick_ag(
 		 * grab.
 		 */
 		if (!max_pag) {
-			for_each_perag_wrap(args->mp, 0, start_agno, args->pag)
+			for_each_perag_wrap(args->mp, 0, start_agno, pag) {
+				max_pag = pag;
 				break;
-			atomic_inc(&args->pag->pagf_fstrms);
-			*longest = 0;
-		} else {
-			pag = max_pag;
-			free = maxfree;
-			atomic_inc(&pag->pagf_fstrms);
+			}
+
+			/* Bail if there are no AGs at all to select from. */
+			if (!max_pag)
+				return -ENOSPC;
 		}
+
+		pag = max_pag;
+		atomic_inc(&pag->pagf_fstrms);
 	} else if (max_pag) {
 		xfs_perag_rele(max_pag);
 	}
 
-	trace_xfs_filestream_pick(pag, pino, free);
+	trace_xfs_filestream_pick(pag, pino);
 	args->pag = pag;
 	return 0;
-
 }
 
 static struct xfs_inode *

fs/xfs/xfs_trace.h

@@ -691,8 +691,8 @@ DEFINE_FILESTREAM_EVENT(xfs_filestream_lookup);
 DEFINE_FILESTREAM_EVENT(xfs_filestream_scan);
 
 TRACE_EVENT(xfs_filestream_pick,
-	TP_PROTO(struct xfs_perag *pag, xfs_ino_t ino, xfs_extlen_t free),
-	TP_ARGS(pag, ino, free),
+	TP_PROTO(struct xfs_perag *pag, xfs_ino_t ino),
+	TP_ARGS(pag, ino),
 	TP_STRUCT__entry(
 		__field(dev_t, dev)
 		__field(xfs_ino_t, ino)
@@ -703,14 +703,9 @@ TRACE_EVENT(xfs_filestream_pick,
 	TP_fast_assign(
 		__entry->dev = pag->pag_mount->m_super->s_dev;
 		__entry->ino = ino;
-		if (pag) {
-			__entry->agno = pag->pag_agno;
-			__entry->streams = atomic_read(&pag->pagf_fstrms);
-		} else {
-			__entry->agno = NULLAGNUMBER;
-			__entry->streams = 0;
-		}
-		__entry->free = free;
+		__entry->agno = pag->pag_agno;
+		__entry->streams = atomic_read(&pag->pagf_fstrms);
+		__entry->free = pag->pagf_freeblks;
 	),
 	TP_printk("dev %d:%d ino 0x%llx agno 0x%x streams %d free %d",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),