linux-kernel - [PATCH] ufs: use ktime_get_real_seconds for sb and cg timestamps

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Date:   Tue, 19 Jun 2018 17:47:21 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Evgeniy Dushistov <dushistov@...l.ru>
Cc:     y2038@...ts.linaro.org, Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jeff Layton <jlayton@...hat.com>,
        David Howells <dhowells@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] ufs: use ktime_get_real_seconds for sb and cg timestamps

get_seconds() is deprecated because of the 32-bit overflow and will
be removed. All callers in ufs also truncate to a 32-bit number, so
nothing changes during the conversion, but this should be harmless as the
superblock and cylinder group timestamps are not visible to user space,
except for checking the fs-dirty state, wich works fine across the
overflow.

This moves the call to get_seconds() into a new inline function, with
a comment explaining the constraints, while converting it to
ktime_get_real_seconds().

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/ufs/balloc.c |  4 ++--
 fs/ufs/ialloc.c |  2 +-
 fs/ufs/super.c  |  4 ++--
 fs/ufs/util.h   | 14 ++++++++++++++
 4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/fs/ufs/balloc.c b/fs/ufs/balloc.c
index e727ee07dbe4..075d3d9114c8 100644
--- a/fs/ufs/balloc.c
+++ b/fs/ufs/balloc.c
@@ -547,7 +547,7 @@ static u64 ufs_add_fragments(struct inode *inode, u64 fragment,
 	/*
 	 * Block can be extended
 	 */
-	ucg->cg_time = cpu_to_fs32(sb, get_seconds());
+	ucg->cg_time = ufs_get_seconds(sb);
 	for (i = newcount; i < (uspi->s_fpb - fragoff); i++)
 		if (ubh_isclr (UCPI_UBH(ucpi), ucpi->c_freeoff, fragno + i))
 			break;
@@ -639,7 +639,7 @@ static u64 ufs_alloc_fragments(struct inode *inode, unsigned cgno,
 	if (!ufs_cg_chkmagic(sb, ucg)) 
 		ufs_panic (sb, "ufs_alloc_fragments",
 			"internal error, bad magic number on cg %u", cgno);
-	ucg->cg_time = cpu_to_fs32(sb, get_seconds());
+	ucg->cg_time = ufs_get_seconds(sb);
 
 	if (count == uspi->s_fpb) {
 		result = ufs_alloccg_block (inode, ucpi, goal, err);
diff --git a/fs/ufs/ialloc.c b/fs/ufs/ialloc.c
index e1ef0f0a1353..c678fff2a04d 100644
--- a/fs/ufs/ialloc.c
+++ b/fs/ufs/ialloc.c
@@ -89,7 +89,7 @@ void ufs_free_inode (struct inode * inode)
 	if (!ufs_cg_chkmagic(sb, ucg))
 		ufs_panic (sb, "ufs_free_fragments", "internal error, bad cg magic number");
 
-	ucg->cg_time = cpu_to_fs32(sb, get_seconds());
+	ucg->cg_time = ufs_get_seconds(sb);
 
 	is_directory = S_ISDIR(inode->i_mode);
 
diff --git a/fs/ufs/super.c b/fs/ufs/super.c
index 488088141451..a4e07e910f1b 100644
--- a/fs/ufs/super.c
+++ b/fs/ufs/super.c
@@ -698,7 +698,7 @@ static int ufs_sync_fs(struct super_block *sb, int wait)
 	usb1 = ubh_get_usb_first(uspi);
 	usb3 = ubh_get_usb_third(uspi);
 
-	usb1->fs_time = cpu_to_fs32(sb, get_seconds());
+	usb1->fs_time = ufs_get_seconds(sb);
 	if ((flags & UFS_ST_MASK) == UFS_ST_SUN  ||
 	    (flags & UFS_ST_MASK) == UFS_ST_SUNOS ||
 	    (flags & UFS_ST_MASK) == UFS_ST_SUNx86)
@@ -1342,7 +1342,7 @@ static int ufs_remount (struct super_block *sb, int *mount_flags, char *data)
 	 */
 	if (*mount_flags & SB_RDONLY) {
 		ufs_put_super_internal(sb);
-		usb1->fs_time = cpu_to_fs32(sb, get_seconds());
+		usb1->fs_time = ufs_get_seconds(sb);
 		if ((flags & UFS_ST_MASK) == UFS_ST_SUN
 		  || (flags & UFS_ST_MASK) == UFS_ST_SUNOS
 		  || (flags & UFS_ST_MASK) == UFS_ST_SUNx86) 
diff --git a/fs/ufs/util.h b/fs/ufs/util.h
index 1907be6d5808..1fd3011ea623 100644
--- a/fs/ufs/util.h
+++ b/fs/ufs/util.h
@@ -590,3 +590,17 @@ static inline int ufs_is_data_ptr_zero(struct ufs_sb_private_info *uspi,
 	else
 		return *(__fs32 *)p == 0;
 }
+
+static inline __fs32 ufs_get_seconds(struct super_block *sbp)
+{
+	time64_t now = ktime_get_real_seconds();
+
+	/* Signed 32-bit interpretation wraps around in 2038, which
+	 * happens in ufs1 inode stamps but not ufs2 using 64-bits
+	 * stamps. For superblock and blockgroup, let's assume
+	 * unsigned 32-bit stamps, which are good until y2106.
+	 * Wrap around rather than clamp here to make the dirty
+	 * file system detection work in the superblock stamp.
+	 */
+	return cpu_to_fs32(sbp, lower_32_bits(now));
+}
-- 
2.9.0