[PATCH v13 4/4] xfs: use current->journal_info to avoid transaction reservation recursion

Yafang Shao
2020-12-17T01:12:34Z

PF_FSTRANS which is used to avoid transaction reservation recursion, is
dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
PF_MEMALLOC_NOFS") and replaced by PF_MEMALLOC_NOFS which means to avoid
filesystem reclaim recursion.

As these two flags have different meanings, we'd better reintroduce
PF_FSTRANS back. To avoid wasting the space of PF_* flags in task_struct,
we can reuse the current->journal_info to do that, per Willy. As the
check of transaction reservation recursion is used by XFS only, we can
move the check into xfs_vm_writepage(s), per Dave.

Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
fs/iomap/buffered-io.c | 7 -------
fs/xfs/xfs_aops.c | 17 +++++++++++++++++
fs/xfs/xfs_trans.h | 26 +++++++++++++++++++-------
3 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 10cc7979ce38..3c53fa6ce64d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1458,13 +1458,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
PF_MEMALLOC))
goto redirty;

- /*
- * Given that we do not allow direct reclaim to call us, we should
- * never be called in a recursive filesystem reclaim context.
- */
- if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
- goto redirty;
-
/*
* Is this page beyond the end of the file?
*
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 2371187b7615..0da0242d42c3 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -568,6 +568,16 @@ xfs_vm_writepage(
{
struct xfs_writepage_ctx wpc = { };

+ /*
+ * Given that we do not allow direct reclaim to call us, we should
+ * never be called while in a filesystem transaction.
+ */
+ if (WARN_ON_ONCE(xfs_trans_context_active())) {
+ redirty_page_for_writepage(wbc, page);
+ unlock_page(page);
+ return 0;
+ }
+
return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);
}

@@ -579,6 +589,13 @@ xfs_vm_writepages(
struct xfs_writepage_ctx wpc = { };

xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
+ /*
+ * Given that we do not allow direct reclaim to call us, we should
+ * never be called while in a filesystem transaction.
+ */
+ if (WARN_ON_ONCE(xfs_trans_context_active()))
+ return 0;
+
return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops);
}

diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 12380eaaf7ce..0c8140147b9b 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -268,29 +268,41 @@ xfs_trans_item_relog(
return lip->li_ops->iop_relog(lip, tp);
}

+static inline bool
+xfs_trans_context_active(void)
+{
+ /* Use journal_info to indicate current is in a transaction */
+ return current->journal_info != NULL;
+}
+
static inline void
xfs_trans_context_set(struct xfs_trans *tp)
{
+ ASSERT(!current->journal_info);
+ current->journal_info = tp;
tp->t_pflags = memalloc_nofs_save();
}

static inline void
xfs_trans_context_clear(struct xfs_trans *tp)
{
+ /*
+ * If xfs_trans_context_swap() handed the NOFS context to a
+ * new transaction we do not clear the context here.
+ */
+ if (current->journal_info != tp)
+ return;
+
+ current->journal_info = NULL;
memalloc_nofs_restore(tp->t_pflags);
}

static inline void
xfs_trans_context_swap(struct xfs_trans *tp, struct xfs_trans *ntp)
{
+ ASSERT(current->journal_info == tp);
+ current->journal_info = ntp;
ntp->t_pflags = tp->t_pflags;
- /*
- * For the rolling transaction, we have to set NOFS in the old
- * transaction's t_pflags so that when we clear the context on
- * the old transaction we don't actually change the thread's NOFS
- * state.
- */
- tp->t_pflags = current->flags | PF_MEMALLOC_NOFS;
}

#endif /* __XFS_TRANS_H__ */
--
2.18.4