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<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Hi ALL,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">This problem is fixed, update info as follows:
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span lang="EN-US" style="color:#1F497D"><span style="mso-list:Ignore">1)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="color:#1F497D">The following patch can fix the problem happened when using the testing code of the previous mail.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US"><a href="https://www.mail-archive.com/ovs-dev@openvswitch.org/msg41202.html">https://www.mail-archive.com/ovs-dev@openvswitch.org/msg41202.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span lang="EN-US" style="color:#1F497D"><span style="mso-list:Ignore">2)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="color:#1F497D">What we need here is a memory_order_acquire sematics when getting impl->size, to make sure, the<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US" style="color:#1F497D">current cpu to get impl->vector content correctly.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span lang="EN-US" style="color:#1F497D"><span style="mso-list:Ignore">3)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="color:#1F497D">The key point here is release/consume, release/require must be used in paired. If ptr is inserted<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US" style="color:#1F497D">into pvec->temp and published later with ovsrcu_set, ovsrcu_get could get the correct pvector->impl->vector<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US" style="color:#1F497D">content (both ptr and *ptr). But sometimes pvector_insert is worked with impl unchanged,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:15.75pt"><span lang="EN-US" style="color:#1F497D">and only release impl->size, so impl->size need to be get use acquire sematics to get correct impl->vector<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:15.75pt"><span lang="EN-US" style="color:#1F497D">content. pvector->size and pvector->vector has no data-dependent relationship, so acquire must be used here, not consume.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>Hi All,<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>Recently we found a problem, as follow:<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>1</span><span style="font-family:宋体;color:#1F497D">．</span><span lang="EN-US" style="color:#1F497D"> Problem description:<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>PVECTOR_FOR_EACH use ovsrcu_get to get pvector’s current impl pointer, and the memory_order_consume<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>in ovsrcu_get will ensure *impl is read after this instruction, so we can get the the correct ptr value in<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>impl->vector[0], but it seems that we cannot make sure that the *ptr value is also correct.<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>2</span><span style="font-family:宋体;color:#1F497D">．</span><span lang="EN-US" style="color:#1F497D"> Verification through testing:<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>Copy the test code into file lib/dpif-netdev.c, and the modify fuction pmd_thread_main, insert the following line<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>in the for (;;) loop</span><span style="font-family:宋体;color:#1F497D">：</span><span style="color:#1F497D">
<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>do_atomic_test(pmd);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> if the do_atomic_consumer is implement without mutex lock, we can easily get the following log in ovs-vswitchd.log:<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> ----my_itrator:143, my_value:144 (we may get other values, and my_itrator = my_value - 1 stay true.<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> The consumer thread can get dirty memory with memory_order_consume, if we change ovsrcu_get to get values<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> with memory_order_acquire, we can still get the error message (my_itrator = my_value - 1).<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>
<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> We can fix this problem if consumer thread access data with g_pvector_lock’ protection, but pvector is designed<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>to use without locks. Where did it go wrong? Can anyone here give some comments?<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>--------------------------------------------- A error case truly happened whining using pvector --------------------------<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>Suppose a scenario as follows:<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>1) handler thread insert a dpcls_subtable, whose address is p,
<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>to datapath classifier’s (struct dpcls) pvector;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>2) pmd thread call fast_path_processing to find the subtable and access address p;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>3) the subtable above is destroyed by someone;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>4) handler thread insert another subtable, whose address is also p,<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>and insert to dpcls’s pvector;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>5) pmd thread call fast_path_processing -> dp_netdev_pmd_lookup_flow<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>-> dpcls_lookup to access the subtable from pvector.<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>We use PVECTOR_FOR_EACH to iterate the pvector in step 5, no locks is used, dirty memory access may<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>cause to ovs-vswitchd process coredump.<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>----------------------------------------------Testing codes are as follows ---------------------------------------------<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static struct pvector g_atomic_test;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static unsigned char g_my_data[65536];<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static unsigned char g_value = 0;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static int g_index = 0;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static struct ovs_mutex g_pvector_lock = OVS_MUTEX_INITIALIZER;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static void do_atomic_producer(void)<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>{<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> ovs_mutex_lock(&g_pvector_lock);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> if (g_index < 65536) {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> g_my_data[g_index] = g_value;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> pvector_insert(&g_atomic_test, (void *)&g_my_data[g_index], 0);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> g_index++;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> } else {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> for (int i = 0; i < g_index; i++) {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> pvector_remove(&g_atomic_test, (void *)&g_my_data[i]);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> }<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> g_index = 0;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> g_value++; //value can loops to zero;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> }<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> pvector_publish(&g_atomic_test);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> ovs_mutex_unlock(&g_pvector_lock);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>}<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static void do_atomic_consumer(void)<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>{<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> unsigned char *my_itr;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> unsigned char my_value;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> bool first = true;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> // ovs_mutex_lock(&g_pvector_lock);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> PVECTOR_FOR_EACH (my_itr, &g_atomic_test) {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> if (first) {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> my_value = *my_itr;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> first = false;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> } else if (*my_itr != my_value) {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> VLOG_ERR("----my_itrator:%u, my_value:%u\n", *my_itr, my_value);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> break;<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> }<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> }<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> // ovs_mutex_unlock(&g_pvector_lock);<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>}<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>static void do_atomic_test(struct dp_netdev_pmd_thread *pmd)<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>{<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> if (pmd->core_id == 1) {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> do_atomic_producer();<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> } else {<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> do_atomic_consumer();<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">> }<o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D">>}</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
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