From: Christoph Hellwig <hch@lst.de>
Date: Tue, 22 Oct 2024 09:38:31 +0000 (+0200)
Subject: xfs: fix finding a last resort AG in xfs_filestream_pick_ag
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=refs%2Fheads%2Fxfs-filesystems-pick-fix;p=users%2Fhch%2Fmisc.git

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.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---

diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index f523027cc325..ecf8a0f6c136 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/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;
 
@@ -113,7 +113,6 @@ restart:
 			     !(flags & XFS_PICK_USERDATA) ||
 			     (flags & XFS_PICK_LOWSPACE))) {
 				/* Break out, retaining the reference on the AG. */
-				free = pag->pagf_freeblks;
 				if (max_pag)
 					xfs_perag_rele(max_pag);
 				goto done;
@@ -149,18 +148,19 @@ restart:
 	 * filestream. It none suit, just use whatever AG we can 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);
 done:
-	trace_xfs_filestream_pick(pag, pino, free);
+	trace_xfs_filestream_pick(pag, pino, pag->pagf_freeblks);
 	args->pag = pag;
 	return 0;