[Bugs] [Bug 1364912] New: The content of file in client is wrong when time was adjusted by NTP in this client.

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1364912

            Bug ID: 1364912
           Summary: The content of file in client is wrong when time was
                    adjusted by NTP in this client.
           Product: GlusterFS
           Version: mainline
         Component: md-cache
          Assignee: bugs at gluster.org
          Reporter: george.lian at nokia.com
             Group: nokia



Description of problem:
 When the system time was adjusted by NTP or others application, md_cache can't
be invalidated while the content of file was changed at same time.

Version-Release number of selected component (if applicable):
mainline

How reproducible:

Let's say VM1,VM2 is a client of storage node.
SN0 is storage node server.

there are a directory which mount with glusterfs type to storage server, let's
say /mnt/sn_mpoint/ on both VM1 and VM2

there is a file in directory /mnt/sn_mpoint , let's say "test_file"
there is only a string "content_in_step1" in the file

Steps to Reproduce:
1. run a command to create a cache for this file in VM1.
    [VM1]# cat /mnt/sn_mpoint/test_file
2. adjust the system time of VM1, now time is hh:mm:ss (assume hh >1)
    [VM1]# date -s hh-1:mm:ss
3. change the content of file in gluster server through action on VM2
    [VM2]# echo "content_in_step3" > /mnt/sn_mpoint/test_file
4. show the content in VM1
    [VM1]# cat /mnt/sn_mpoint/test_file
Actual results:
"content_in_step1"

Expected results:
"content_in_step3"

Additional info:

after investigation, there a function called "is_md_cache_xatt_valid" 
static gf_boolean_t
is_md_cache_xatt_valid (xlator_t *this, struct md_cache *mdc)
{
    struct mdc_conf *conf = NULL;
    time_t           now = 0;
        gf_boolean_t     ret = _gf_true;

    conf = this->private;

    time (&now);

        LOCK (&mdc->lock);
        {
//                if (now >= (mdc->xa_time + conf->timeout))
                  if (now >= (mdc->xa_time + conf->timeout) || now <
(mdc->xa_time)
                        ret = _gf_false;
        }
        UNLOCK (&mdc->lock);

    return ret;
}

I try change the line which commented to the new one, which mean do invalidate
for this cache when current time is young than mdc's cache time, and I have
verified the changes, the issue seems gone. 
there are 2 other function "is_md_cache_iatt_valid" and "__qr_cache_is_fresh"
seems have same issues.

I dont' think my changes is the best solutions for this issue, just for your
reference, and wish your comments and right solutions for this issue.

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