The patch titled
writeback: guard against jiffies wraparound on inode->dirtied_when checks (try #2)
has been added to the -mm tree. Its filename is
writeback-guard-against-jiffies-wraparound-on-inode-dirtied_when-checks-try-2.patch
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Subject: writeback: guard against jiffies wraparound on inode->dirtied_when checks (try #2)
From: Jeff Layton <jlayton@xxxxxxxxxx>
This is the second version of this patch. The only difference from the
first version is the addition of some comments.
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Ian Kent <raven@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff -puN fs/fs-writeback.c~writeback-guard-against-jiffies-wraparound-on-inode-dirtied_when-checks-try-2 fs/fs-writeback.c
--- a/fs/fs-writeback.c~writeback-guard-against-jiffies-wraparound-on-inode-dirtied_when-checks-try-2
+++ a/fs/fs-writeback.c
@@ -196,6 +196,10 @@ static void redirty_tail(struct inode *i
struct inode *tail_inode;
tail_inode = list_entry(sb->s_dirty.next, struct inode, i_list);
+ /*
+ * must also check whether dirtied_when appears to be in the
+ * future, in which case it's actually in the distant past.
+ */
if (time_before(inode->dirtied_when,
tail_inode->dirtied_when) ||
time_after(inode->dirtied_when, jiffies))
@@ -231,6 +235,10 @@ static void move_expired_inodes(struct l
while (!list_empty(delaying_queue)) {
struct inode *inode = list_entry(delaying_queue->prev,
struct inode, i_list);
+ /*
+ * must also check whether dirtied_when appears to be in the
+ * future, in which case it's actually in the distant past.
+ */
if (older_than_this &&
time_after(inode->dirtied_when, *older_than_this) &&
time_before_eq(inode->dirtied_when, jiffies))
@@ -494,7 +502,18 @@ void generic_sync_sb_inodes(struct super
continue; /* blockdev has wrong queue */
}
- /* Was this inode dirtied after sync_sb_inodes was called? */
+ /*
+ * Was this inode dirtied after sync_sb_inodes was called?
+ *
+ * It's not sufficient to just do a time_after() check on
+ * dirtied_when. That assumes that dirtied_when will always
+ * change within a period of jiffies that encompasses half the
+ * machine word size (2^31 jiffies on 32-bit arch). That's not
+ * necessarily the case if an inode is being constantly
+ * redirtied. Since dirtied_when can never be in the future,
+ * we can assume that if it appears to be so then it is
+ * actually in the distant past.
+ */
if (time_after(inode->dirtied_when, start) &&
time_before_eq(inode->dirtied_when, jiffies))
break;
_
Patches currently in -mm which might be from jlayton@xxxxxxxxxx are
origin.patch
writeback-guard-against-jiffies-wraparound-on-inode-dirtied_when-checks.patch
writeback-guard-against-jiffies-wraparound-on-inode-dirtied_when-checks-try-2.patch
linux-next.patch
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