[PATCH 1/4] libxfs: fix uncached buffer refcounting

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: sandeen@sandeen.net, darrick.wong@oracle.com
Cc: linux-xfs@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: [PATCH 1/4] libxfs: fix uncached buffer refcounting
Date: Mon, 26 Aug 2019 14:21:46 -0700	[thread overview]
Message-ID: <156685450680.2840210.3212526932977200554.stgit@magnolia> (raw)
In-Reply-To: <156685449440.2840210.11908449959921635294.stgit@magnolia>

From: Darrick J. Wong <darrick.wong@oracle.com>

Currently, uncached buffers in userspace are created with zero refcount
and are fed to cache_node_put when they're released.  This is totally
broken -- the refcount should be 1 (because the caller now holds a
reference) and we should never be dumping uncached buffers into the
cache.  Fix both of these problems.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 libxfs/libxfs_io.h   |   18 ++++++++++++++++++
 libxfs/libxfs_priv.h |    2 --
 libxfs/rdwr.c        |    5 ++++-
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/libxfs/libxfs_io.h b/libxfs/libxfs_io.h
index 0b8d9774..7dcb4bff 100644
--- a/libxfs/libxfs_io.h
+++ b/libxfs/libxfs_io.h
@@ -227,4 +227,22 @@ xfs_buf_associate_memory(struct xfs_buf *bp, void *mem, size_t len)
 	return 0;
 }
 
+/*
+ * Allocate an uncached buffer that points nowhere.  The refcount will be 1,
+ * and the cache node hash list will be empty to indicate that it's uncached.
+ */
+static inline struct xfs_buf *
+xfs_buf_get_uncached(struct xfs_buftarg *targ, size_t bblen, int flags)
+{
+	struct xfs_buf	*bp;
+
+	bp = libxfs_getbufr(targ, XFS_BUF_DADDR_NULL, bblen);
+	if (!bp)
+		return NULL;
+
+	INIT_LIST_HEAD(&bp->b_node.cn_hash);
+	bp->b_node.cn_count = 1;
+	return bp;
+}
+
 #endif	/* __LIBXFS_IO_H__ */
diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index 8b3de170..99cfac1f 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -379,8 +379,6 @@ roundup_64(uint64_t x, uint32_t y)
 	(len) = __bar; /* no set-but-unused warning */	\
 	NULL;						\
 })
-#define xfs_buf_get_uncached(t,n,f)     \
-	libxfs_getbufr((t), XFS_BUF_DADDR_NULL, (n));
 #define xfs_buf_relse(bp)		libxfs_putbuf(bp)
 #define xfs_buf_get(devp,blkno,len)	(libxfs_getbuf((devp), (blkno), (len)))
 #define xfs_bwrite(bp)			libxfs_writebuf((bp), 0)
diff --git a/libxfs/rdwr.c b/libxfs/rdwr.c
index 1f2c129b..3282f6de 100644
--- a/libxfs/rdwr.c
+++ b/libxfs/rdwr.c
@@ -867,7 +867,10 @@ libxfs_putbuf(xfs_buf_t *bp)
 		}
 	}
 
-	cache_node_put(libxfs_bcache, (struct cache_node *)bp);
+	if (!list_empty(&bp->b_node.cn_hash))
+		cache_node_put(libxfs_bcache, (struct cache_node *)bp);
+	else if (--bp->b_node.cn_count == 0)
+		libxfs_putbufr(bp);
 }
 
 void

