On Tue, Feb 20, 2024 at 08:28:21AM +0100, Christoph Hellwig wrote:
> So we should be fine here, but the code could really use documentation,
> a few more asserts and a slightly different structure that makes this
> more obvious. I'll throw in a patch for that.
This is what I ended up with:
---
>From 22cba925f1f94b22cfa6143a814f1d14a3521621 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@xxxxxx>
Date: Tue, 20 Feb 2024 08:35:27 +0100
Subject: xfs: block deltas in xfs_trans_unreserve_and_mod_sb must be positive
And to make that more clear, rearrange the code a bit and add asserts
and a comment.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
fs/xfs/xfs_trans.c | 38 ++++++++++++++++++++++++--------------
1 file changed, 24 insertions(+), 14 deletions(-)
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 12d45e93f07d50..befb508638ca1f 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -594,28 +594,38 @@ xfs_trans_unreserve_and_mod_sb(
{
struct xfs_mount *mp = tp->t_mountp;
bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
- int64_t blkdelta = 0;
- int64_t rtxdelta = 0;
+ int64_t blkdelta = tp->t_blk_res;
+ int64_t rtxdelta = tp->t_rtx_res;
int64_t idelta = 0;
int64_t ifreedelta = 0;
int error;
- /* calculate deltas */
- if (tp->t_blk_res > 0)
- blkdelta = tp->t_blk_res;
- if ((tp->t_fdblocks_delta != 0) &&
- (xfs_has_lazysbcount(mp) ||
- (tp->t_flags & XFS_TRANS_SB_DIRTY)))
+ /*
+ * Calculate the deltas.
+ *
+ * t_fdblocks_delta and t_frextents_delta can be positive or negative:
+ *
+ * - positive values indicate blocks freed in the transaction.
+ * - negative values indicate blocks allocated in the transaction
+ *
+ * Negative values can only happen if the transaction has a block
+ * reservation that covers the allocated block. The end result is
+ * that the calculated delta values must always be positive and we
+ * can only put back previous allocated or reserved blocks here.
+ */
+ ASSERT(tp->t_blk_res || tp->t_fdblocks_delta >= 0);
+ if (xfs_has_lazysbcount(mp) || (tp->t_flags & XFS_TRANS_SB_DIRTY)) {
blkdelta += tp->t_fdblocks_delta;
+ ASSERT(blkdelta >= 0);
+ }
- if (tp->t_rtx_res > 0)
- rtxdelta = tp->t_rtx_res;
- if ((tp->t_frextents_delta != 0) &&
- (tp->t_flags & XFS_TRANS_SB_DIRTY))
+ ASSERT(tp->t_rtx_res || tp->t_frextents_delta >= 0);
+ if (tp->t_flags & XFS_TRANS_SB_DIRTY) {
rtxdelta += tp->t_frextents_delta;
+ ASSERT(rtxdelta >= 0);
+ }
- if (xfs_has_lazysbcount(mp) ||
- (tp->t_flags & XFS_TRANS_SB_DIRTY)) {
+ if (xfs_has_lazysbcount(mp) || (tp->t_flags & XFS_TRANS_SB_DIRTY)) {
idelta = tp->t_icount_delta;
ifreedelta = tp->t_ifree_delta;
}
--
2.39.2
