linux-kernel - [PATCH v3 11/13] fs: use smp_load_acquire in break

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Date:   Thu, 19 Oct 2017 19:39:57 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     akpm@...ux-foundation.org
Cc:     linux-xfs@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org, hch@....de,
        "J. Bruce Fields" <bfields@...ldses.org>, linux-mm@...ck.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        Jeff Layton <jlayton@...chiereds.net>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: [PATCH v3 11/13] fs: use smp_load_acquire in break_{layout,lease}

Commit 128a37852234 "fs: fix data races on inode->i_flctx" converted
checks of inode->i_flctx to use smp_load_acquire(), but it did not
convert break_layout(). smp_load_acquire() includes a READ_ONCE(). There
should be no functional difference since __break_lease repeats the
sequence, but this is a clean up to unify all ->i_flctx lookups on a
common pattern.

Cc: Christoph Hellwig <hch@....de>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: Jeff Layton <jlayton@...chiereds.net>
Cc: "J. Bruce Fields" <bfields@...ldses.org>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 include/linux/fs.h |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 13dab191a23e..eace2c5396a7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2281,8 +2281,9 @@ static inline int break_lease(struct inode *inode, unsigned int mode)
 	 * could end up racing with tasks trying to set a new lease on this
 	 * file.
 	 */
-	smp_mb();
-	if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease))
+	struct file_lock_context *ctx = smp_load_acquire(&inode->i_flctx);
+
+	if (ctx && !list_empty_careful(&ctx->flc_lease))
 		return __break_lease(inode, mode, FL_LEASE);
 	return 0;
 }
@@ -2325,8 +2326,9 @@ static inline int break_deleg_wait(struct inode **delegated_inode)
 
 static inline int break_layout(struct inode *inode, bool wait)
 {
-	smp_mb();
-	if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease))
+	struct file_lock_context *ctx = smp_load_acquire(&inode->i_flctx);
+
+	if (ctx && !list_empty_careful(&ctx->flc_lease))
 		return __break_lease(inode,
 				wait ? O_WRONLY : O_WRONLY | O_NONBLOCK,
 				FL_LAYOUT);