xfs: use WRITE_ONCE to update if_seq

This adds ordering of the updates and makes sure we always see the if_seq
update before the extent tree is modified.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/libxfs/xfs_iext_tree.c b/fs/xfs/libxfs/xfs_iext_tree.c
index 8a7aea0..771dd07 100644 (file)
--- a/fs/xfs/libxfs/xfs_iext_tree.c
+++ b/fs/xfs/libxfs/xfs_iext_tree.c
@@ -14,6 +14,7 @@
 #include "xfs_inode_fork.h"
 #include "xfs_trans_resv.h"
 #include "xfs_mount.h"
+#include "xfs_bmap.h"
 #include "xfs_trace.h"
 
 /*
@@ -612,6 +613,19 @@ xfs_iext_realloc_root(
        cur->leaf = new;
 }
 
+/*
+ * Increment the sequence counter if we are on a COW fork.  This allows
+ * the writeback code to skip looking for a COW extent if the COW fork
+ * hasn't changed.  We use WRITE_ONCE here to ensure the update to the
+ * sequence counter is seen before the modifications to the extent
+ * tree itself take effect.
+ */
+static inline void xfs_iext_inc_seq(struct xfs_ifork *ifp, int state)
+{
+       if (state & BMAP_COWFORK)
+               WRITE_ONCE(ifp->if_seq, READ_ONCE(ifp->if_seq) + 1);
+}
+
 void
 xfs_iext_insert(
        struct xfs_inode        *ip,
@@ -624,7 +638,7 @@ xfs_iext_insert(
        struct xfs_iext_leaf    *new = NULL;
        int                     nr_entries, i;
 
-       ifp->if_seq++;
+       xfs_iext_inc_seq(ifp, state);
 
        if (ifp->if_height == 0)
                xfs_iext_alloc_root(ifp, cur);
@@ -866,7 +880,7 @@ xfs_iext_remove(
        ASSERT(ifp->if_u1.if_root != NULL);
        ASSERT(xfs_iext_valid(ifp, cur));
 
-       ifp->if_seq++;
+       xfs_iext_inc_seq(ifp, state);
 
        nr_entries = xfs_iext_leaf_nr_entries(ifp, leaf, cur->pos) - 1;
        for (i = cur->pos; i < nr_entries; i++)
@@ -974,7 +988,7 @@ xfs_iext_update_extent(
 {
        struct xfs_ifork        *ifp = xfs_iext_state_to_fork(ip, state);
 
-       ifp->if_seq++;
+       xfs_iext_inc_seq(ifp, state);
 
        if (cur->pos == 0) {
                struct xfs_bmbt_irec    old;

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 235b4dd..49f5f58 100644 (file)
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -351,7 +351,7 @@ xfs_map_blocks(
        if (imap_valid &&
            (!xfs_inode_has_cow_data(ip) ||
             wpc->io_type == XFS_IO_COW ||
-            wpc->cow_seq == ip->i_cowfp->if_seq))
+            wpc->cow_seq == READ_ONCE(ip->i_cowfp->if_seq)))
                return 0;
 
        if (XFS_FORCED_SHUTDOWN(mp))
@@ -380,7 +380,7 @@ xfs_map_blocks(
            xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap))
                cow_fsb = imap.br_startoff;
        if (cow_fsb != NULLFILEOFF && cow_fsb <= offset_fsb) {
-               wpc->cow_seq = ip->i_cowfp->if_seq;
+               wpc->cow_seq = READ_ONCE(ip->i_cowfp->if_seq);
                xfs_iunlock(ip, XFS_ILOCK_SHARED);
                /*
                 * Truncate can race with writeback since writeback doesn't

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 3282575..6320aca 100644 (file)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -655,6 +655,7 @@ xfs_iomap_write_allocate(
        unsigned int    *cow_seq)
 {
        xfs_mount_t     *mp = ip->i_mount;
+       struct xfs_ifork *ifp = XFS_IFORK_PTR(ip, whichfork);
        xfs_fileoff_t   offset_fsb, last_block;
        xfs_fileoff_t   end_fsb, map_start_fsb;
        xfs_filblks_t   count_fsb;
@@ -768,7 +769,7 @@ xfs_iomap_write_allocate(
                                goto error0;
 
                        if (whichfork == XFS_COW_FORK)
-                               *cow_seq = XFS_IFORK_PTR(ip, whichfork)->if_seq;
+                               *cow_seq = READ_ONCE(ifp->if_seq);
                        xfs_iunlock(ip, XFS_ILOCK_EXCL);
                }