xfs: hold xfs_buf locked between shortform->leaf conversion and the addition of an...

Source kernel commit: 6e643cd094de3bd0f97edcc1db0089afa24d909f

The new attribute leaf buffer is not held locked across the transaction
roll between the shortform->leaf modification and the addition of the
new entry.  As a result, the attribute buffer modification being made is
not atomic from an operational perspective.  Hence the AIL push can grab
it in the transient state of "just created" after the initial
transaction is rolled, because the buffer has been released.  This leads
to xfs_attr3_leaf_verify() asserting that hdr.count is zero, treating
this as in-memory corruption, and shutting down the filesystem.

Darrick ported the original patch to 4.15 and reworked it use the
xfs_defer_bjoin helper and hold/join the buffer correctly across the
second transaction roll.

Signed-off-by: Alex Lyakas <alex@zadarastorage.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/libxfs/xfs_attr.c b/libxfs/xfs_attr.c
index 8d0abcc120e8877ab073a553a24dbecd074a8239..452244723078b04380a8732c7030a1042d9753de 100644 (file)
--- a/libxfs/xfs_attr.c
+++ b/libxfs/xfs_attr.c
@@ -207,6 +207,7 @@ xfs_attr_set(
        int                     flags)
 {
        struct xfs_mount        *mp = dp->i_mount;
+       struct xfs_buf          *leaf_bp = NULL;
        struct xfs_da_args      args;
        struct xfs_defer_ops    dfops;
        struct xfs_trans_res    tres;
@@ -322,9 +323,16 @@ xfs_attr_set(
                 * GROT: another possible req'mt for a double-split btree op.
                 */
                xfs_defer_init(args.dfops, args.firstblock);
-               error = xfs_attr_shortform_to_leaf(&args);
+               error = xfs_attr_shortform_to_leaf(&args, &leaf_bp);
                if (error)
                        goto out_defer_cancel;
+               /*
+                * Prevent the leaf buffer from being unlocked so that a
+                * concurrent AIL push cannot grab the half-baked leaf
+                * buffer and run into problems with the write verifier.
+                */
+               xfs_trans_bhold(args.trans, leaf_bp);
+               xfs_defer_bjoin(args.dfops, leaf_bp);
                xfs_defer_ijoin(args.dfops, dp);
                error = xfs_defer_finish(&args.trans, args.dfops);
                if (error)
@@ -332,13 +340,14 @@ xfs_attr_set(
 
                /*
                 * Commit the leaf transformation.  We'll need another (linked)
-                * transaction to add the new attribute to the leaf.
+                * transaction to add the new attribute to the leaf, which
+                * means that we have to hold & join the leaf buffer here too.
                 */
-
                error = xfs_trans_roll_inode(&args.trans, dp);
                if (error)
                        goto out;
-
+               xfs_trans_bjoin(args.trans, leaf_bp);
+               leaf_bp = NULL;
        }
 
        if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
@@ -369,8 +378,9 @@ xfs_attr_set(
 
 out_defer_cancel:
        xfs_defer_cancel(&dfops);
-       args.trans = NULL;
 out:
+       if (leaf_bp)
+               xfs_trans_brelse(args.trans, leaf_bp);
        if (args.trans)
                xfs_trans_cancel(args.trans);
        xfs_iunlock(dp, XFS_ILOCK_EXCL);

diff --git a/libxfs/xfs_attr_leaf.c b/libxfs/xfs_attr_leaf.c
index 83d4f501ff4e2eb4c0a3d3dc0800c7e9da9d3a5d..2f2456717e1ef4504ca812c95afd391ba71e39a4 100644 (file)
--- a/libxfs/xfs_attr_leaf.c
+++ b/libxfs/xfs_attr_leaf.c
@@ -730,10 +730,13 @@ xfs_attr_shortform_getvalue(xfs_da_args_t *args)
 }
 
 /*
- * Convert from using the shortform to the leaf.
+ * Convert from using the shortform to the leaf.  On success, return the
+ * buffer so that we can keep it locked until we're totally done with it.
  */
 int
-xfs_attr_shortform_to_leaf(xfs_da_args_t *args)
+xfs_attr_shortform_to_leaf(
+       struct xfs_da_args      *args,
+       struct xfs_buf          **leaf_bp)
 {
        xfs_inode_t *dp;
        xfs_attr_shortform_t *sf;
@@ -813,7 +816,7 @@ xfs_attr_shortform_to_leaf(xfs_da_args_t *args)
                sfe = XFS_ATTR_SF_NEXTENTRY(sfe);
        }
        error = 0;
-
+       *leaf_bp = bp;
 out:
        kmem_free(tmpbuffer);
        return error;

diff --git a/libxfs/xfs_attr_leaf.h b/libxfs/xfs_attr_leaf.h
index f7dda0c237b044b166d6d178fca3178feff2b644..894124efb421e0d0674b0f39bf63dabfe7916937 100644 (file)
--- a/libxfs/xfs_attr_leaf.h
+++ b/libxfs/xfs_attr_leaf.h
@@ -48,7 +48,8 @@ void  xfs_attr_shortform_create(struct xfs_da_args *args);
 void   xfs_attr_shortform_add(struct xfs_da_args *args, int forkoff);
 int    xfs_attr_shortform_lookup(struct xfs_da_args *args);
 int    xfs_attr_shortform_getvalue(struct xfs_da_args *args);
-int    xfs_attr_shortform_to_leaf(struct xfs_da_args *args);
+int    xfs_attr_shortform_to_leaf(struct xfs_da_args *args,
+                       struct xfs_buf **leaf_bp);
 int    xfs_attr_shortform_remove(struct xfs_da_args *args);
 int    xfs_attr_shortform_allfit(struct xfs_buf *bp, struct xfs_inode *dp);
 int    xfs_attr_shortform_bytesfit(struct xfs_inode *dp, int bytes);