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Subject[PATCH 06/13] tmpfs: time granularity fix for [acm]time going backwards
-stable review patch.  If anyone has any objections, please let us know.
From: Robin H. Johnson <>

I noticed a strange behavior in a tmpfs file system the other day, while
building packages - occasionally, and seemingly at random, make decided to
rebuild a target. However, only on tmpfs.

A file would be created, and if checked, it had a sub-second timestamp.
However, after an utimes related call where sub-seconds should be set, they
were zeroed instead. In the case that a file was created, and utimes(...,NULL)
was used on it in the same second, the timestamp on the file moved backwards.

After some digging, I found that this was being caused by tmpfs not having a
time granularity set, thus inheriting the default 1 second granularity.

Hugh adds: yes, we missed tmpfs when the s_time_gran mods went into 2.6.11.
Unfortunately, the granularity of CURRENT_TIME, often used in filesystems,
does not match the default granularity set by alloc_super. A few more such
discrepancies have been found, but this is the most important to fix now.

Signed-off-by: Robin H. Johnson <>
Acked-by: Andi Kleen <>
Signed-off-by: Hugh Dickins <>
Signed-off-by: Chris Wright <>
Signed-off-by: Greg Kroah-Hartman <>
mm/shmem.c | 1 +
1 file changed, 1 insertion(+)
--- linux-
+++ linux-
@@ -2100,6 +2100,7 @@ static int shmem_fill_super(struct super
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = TMPFS_MAGIC;
sb->s_op = &shmem_ops;
+ sb->s_time_gran = 1;

inode = shmem_get_inode(sb, S_IFDIR | mode, 0);
if (!inode)
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