https://jira.whamcloud.com This file is an XML representation of an issue en-us 9.4.14 940014 05-12-2023 https://jira.whamcloud.com/browse/LU-3055 Lustre <p>By running the Coverity tool on the Lustre code, we may have found a possible thread deadlock.</p> <p>In function put_pages_on_daemon_list(), the loop with cfs_tcd_for_each_type_lock() acquires the lock "cfs_trace_cpu_data.tcd_lock". And inside this loop, the call to put_pages_on_tcd_daemon_list() acquires the lock "page_collection.pc_lock".</p> <p>However, we have two other cases where the locks tcd_lock and pc_lock are taken in reverse order.<br/> In collect_pages_on_all_cpus(), spin_lock(&amp;pc-&gt;pc_lock) acquires the lock "pc-&gt;pc_lock", and then the loop with cfs_tcd_for_each_type_lock() acquires the lock "cfs_trace_cpu_data.tcd_lock".<br/> We have the same situation in put_pages_back_on_all_cpus().</p> <p>In the end it seems a thread deadlock could occur. What do you think?</p> <p>Sebastien.</p> LU-3055

Possible deadlock in put_pages_on_daemon_list()

Technical task LU-2753 Minor Resolved Fixed Liang Zhen Sebastien Buisson coverity Thu, 28 Mar 2013 15:48:48 +0000 Fri, 25 Oct 2013 13:23:31 +0000 Fri, 25 Oct 2013 13:23:31 +0000 Lustre 2.4.0 Lustre 2.6.0 0 5 <p>Liang</p> <p>Are you able to comment?</p> <p>Thanks</p> <p>Peter</p> <p>This code is not very clean, but it's impossible to deadlock:</p> <ul> <li>put_pages_on_daemon_list() is only called by kthread tracefiled(), and @pc here is a structure in thread stack</li> <li>the only chance that the same @pc can be referred by collect_pages_on_all_cpus() is, the thread thread call collect_pages()-&gt;&gt;collect_pages_on_all_cpus()</li> </ul> <p>so @pc is not going to be shared between different threads.<br/> Actually, after I looked into code, I think pc_lock is totally useless, it's there because we used to have a function trace_call_on_all_cpus() and it's supposed to protect race between CPUs (see BZ15878), now all use-cases of page_collection are actually just per-thread and in-stack, so we can simply remove this lock.</p> <p>patch is ready to land: <a href="http://review.whamcloud.com/#/c/7660/" class="external-link" target="_blank" rel="nofollow noopener">http://review.whamcloud.com/#/c/7660/</a></p> <p>Landed for 2.6</p> Development Rank 1|hzvmkf: Rank (Obsolete) 7449