On Fri, Oct 13, 2017 at 12:01:22PM +1100, Dave Chinner wrote:

On Wed, Oct 11, 2017 at 06:41:07PM -0700, Darrick J. Wong wrote:

quoted

From: Darrick J. Wong <redacted>

Refactor the btree block header checks to have an internal function that
returns the address of the failing check without logging errors.  The
scrubber will call the internal function, while the external version
will maintain the current logging behavior.

.....

quoted

diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
index 8f52eda..baf7064 100644
--- a/fs/xfs/libxfs/xfs_btree.h
+++ b/fs/xfs/libxfs/xfs_btree.h

@@ -255,6 +255,11 @@ typedef struct xfs_btree_cur
  */
 #define	XFS_BUF_TO_BLOCK(bp)	((struct xfs_btree_block *)((bp)->b_addr))
 
+/* Internal long and short btree block checks. */
+void *__xfs_btree_check_lblock(struct xfs_btree_cur *cur,
+		struct xfs_btree_block *block, int level, struct xfs_buf *bp);
+void *__xfs_btree_check_sblock(struct xfs_btree_cur *cur,
+		struct xfs_btree_block *block, int level, struct xfs_buf *bp);

/*
 * Internal long and short btree block checks. They return NULL if
 * the block is OK, otherwise they return the address of the failed
 * check.
 */

Ok.

quoted

 
 /*
  * Check that block header is ok.

diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index dcd1292..b825953 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h

@@ -142,6 +142,13 @@ typedef __u32			xfs_nlink_t;
 #define SYNCHRONIZE()	barrier()
 #define __return_address __builtin_return_address(0)
 
+/*
+ * Return the address of a label.  Use asm volatile so that the optimizer
+ * won't try anything stupid like refactoring the error jumpouts into a
+ * single return, which throws off the reported address.
+ */
+#define __this_address  ({ __label__ __here; __here: asm volatile(""); &&__here; })

I think this should probably use barrier() rather than an asm
statement - can you check that this works correctly with gcc?  Other
compilers won't work with a asm statement (llvm/intel) but should
DTRT with a compiler barrier intrinsic...

Ok.  The asm output is identical under asm volatile/barrier, at least on gcc.

--D

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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