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<p class="MsoNormal">Hello, <br>
<br>
When I wanted to change the state of DRBD from primary to secondary, sometimes I get the "Device is held open by someone" issue.
<br>
I looked into the code <b>drbd_main.c</b> (<b>DRBD Release 8.0.11</b>) and found that the error is set from the below code.<br>
<br>
<b>else if( ns.role == Secondary && mdev->open_cnt )<br>
rv=SS_DeviceInUse; <br>
</b><br>
I put debug logs and found that sometimes "open_cnt" variable is not equal to zero that results in the error. "open_cnt" variable is incremented and decremented from the function
<b>drbd_open()</b> and <b>drbd_close()</b> respectively. In function <b>drbd_open()</b>, "open_cnt" variable is handled within locking/unlocking function to avoid race condition whereas in
<b>drbd_close()</b>, no such locking/unlocking function is there to handle its critical section. Can we imagine any scenario that due to the absence of locking/unlocking function in the
<b>drbd_close()</b> function, race condition is occurring that results in the wrong value of "open_cnt" variable.<br>
<br>
Here is the code.<span style="font-size:12.0pt;font-family:"Times New Roman","serif"">
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:8.0pt">STATIC int drbd_close(struct inode *inode, struct file *file)</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt">{</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> /* do not use *file (May be NULL, in case of a unmount :-) */</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> drbd_dev *mdev;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> mdev = minor_to_mdev(MINOR(inode->i_rdev));</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> if(!mdev) return -ENODEV;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> /*</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> printk(KERN_ERR DEVICE_NAME ": close(inode=%p,file=%p)"</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> "current=%p,minor=%d,wc=%d\n", inode, file, current, minor,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> inode->i_writecount);</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> */</span><o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> <span style="background:yellow">
mdev->open_cnt--;</span></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> return 0;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt">}</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt">STATIC int drbd_open(struct inode *inode, struct file *file)</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt">{</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> drbd_dev *mdev;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> unsigned long flags;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> int rv=0;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> mdev = minor_to_mdev(MINOR(inode->i_rdev));</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> if(!mdev) return -ENODEV;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> <span style="background:yellow">
spin_lock_irqsave(&mdev->req_lock,flags);</span></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> /* to have a stable mdev->state.role and no race with updating open_cnt */</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> if (mdev->state.role != Primary) {</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> if (file->f_mode & FMODE_WRITE) {</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> rv = -EROFS;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> } else if (!allow_oos) {</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> rv = -EMEDIUMTYPE;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> }</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> }</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> <span style="background:yellow">
if(!rv) mdev->open_cnt++;</span></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> <span style="background:yellow">
spin_unlock_irqrestore(&mdev->req_lock,flags);</span></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> return rv;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt">}</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:8.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<p class="MsoNormal">Thanks in Advance.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Regards,<o:p></o:p></p>
<p class="MsoNormal">Satyajit Paul<o:p></o:p></p>
<p class="MsoNormal">Software Engineer<o:p></o:p></p>
<p class="MsoNormal">India<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""> </span><o:p></o:p></p>
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