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From: Yafang Shao <laoar.shao@gmail.com>
To: darrick.wong@oracle.com, willy@infradead.org,
	david@fromorbit.com, hch@infradead.org, mhocko@kernel.org,
	akpm@linux-foundation.org, dhowells@redhat.com,
	jlayton@redhat.com
Cc: linux-fsdevel@vger.kernel.org, linux-cachefs@redhat.com,
	linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	Yafang Shao <laoar.shao@gmail.com>,
	Christoph Hellwig <hch@lst.de>
Subject: [PATCH v10 4/4] xfs: use current->journal_info to avoid transaction reservation recursion
Date: Tue,  8 Dec 2020 10:15:43 +0800	[thread overview]
Message-ID: <20201208021543.76501-5-laoar.shao@gmail.com> (raw)
In-Reply-To: <20201208021543.76501-1-laoar.shao@gmail.com>

PF_FSTRANS which is used to avoid transaction reservation recursion, is
dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce
memalloc_nofs_{save,restore} API") 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.

To better abstract that behavoir, two new helpers are introduced, as
follows,
- xfs_trans_context_active
  To check whehter current is in fs transcation or not
- xfs_trans_context_swap
  Transfer the transaction context when rolling a permanent transaction

These two new helpers are instroduced in xfs_trans.h.

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.c     |  3 +++
 fs/xfs/xfs_trans.h     | 25 +++++++++++++++++++++++++
 4 files changed, 45 insertions(+), 7 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..28db93d0da97 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 (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 (xfs_trans_context_active())
+		return 0;
+
 	return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops);
 }
 
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index fe20398a214e..08d4916ffb13 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -124,6 +124,9 @@ xfs_trans_dup(
 	tp->t_rtx_res = tp->t_rtx_res_used;
 	ntp->t_pflags = tp->t_pflags;
 
+	/* Associate the new transaction with this thread. */
+	xfs_trans_context_swap(tp, ntp);
+
 	/* move deferred ops over to the new tp */
 	xfs_defer_move(ntp, tp);
 
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 44b11c64a15e..82c6735e40fc 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -268,16 +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 */
+	if (WARN_ON_ONCE(current->journal_info != NULL))
+		return true;
+
+	return false;
+}
+
 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)
 {
+	ASSERT(current->journal_info == tp);
+	current->journal_info = NULL;
 	memalloc_nofs_restore(tp->t_pflags);
 }
 
+/*
+ * Transfer the transaction context when rolling a permanent
+ * transaction.
+ */
+static inline void
+xfs_trans_context_swap(struct xfs_trans *tp, struct xfs_trans *ntp)
+{
+	ASSERT(current->journal_info == tp);
+	current->journal_info = ntp;
+}
+
 #endif	/* __XFS_TRANS_H__ */
-- 
2.18.4



  parent reply	other threads:[~2020-12-08  2:16 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08  2:15 [PATCH v10 0/4] xfs: avoid transaction reservation recursion Yafang Shao
2020-12-08  2:15 ` [PATCH v10 1/4] mm: Add become_kswapd and restore_kswapd Yafang Shao
2020-12-08  2:15 ` [PATCH v10 2/4] xfs: use memalloc_nofs_{save,restore} in xfs transaction Yafang Shao
2020-12-08  2:46   ` Matthew Wilcox
2020-12-08  3:05     ` Yafang Shao
2020-12-08  2:15 ` [PATCH v10 3/4] xfs: refactor the usage around xfs_trans_context_{set,clear} Yafang Shao
2020-12-08  2:15 ` Yafang Shao [this message]
2020-12-08  2:41   ` [PATCH v10 4/4] xfs: use current->journal_info to avoid transaction reservation recursion Matthew Wilcox
2020-12-08  3:03     ` Yafang Shao
2020-12-08  4:20   ` Dave Chinner
2020-12-08  5:01     ` Yafang Shao

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