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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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