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<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>LKML: Dinakar Guniguntala: Recursion bug in -rt</title><link href="/css/message.css" rel="stylesheet" type="text/css" /><link href="/css/wrap.css" rel="alternate stylesheet" type="text/css" title="wrap" /><link href="/css/nowrap.css" rel="stylesheet" type="text/css" title="nowrap" /><link href="/favicon.ico" rel="shortcut icon" /><script src="/js/simple-calendar.js" type="text/javascript"></script><script src="/js/styleswitcher.js" type="text/javascript"></script><link rel="alternate" type="application/rss+xml" title="lkml.org : last 100 messages" href="/rss.php" /><link rel="alternate" type="application/rss+xml" title="lkml.org : last messages by Dinakar Guniguntala" href="/groupie.php?aid=23410" /><script> var _paq = window._paq = window._paq || []; /* tracker methods like "setCustomDimension" should be called before "trackPageView" */ _paq.push(["setDoNotTrack", true]); _paq.push(["disableCookies"]); _paq.push(['trackPageView']); _paq.push(['enableLinkTracking']); (function() { var u="//m.lkml.org/"; _paq.push(['setTrackerUrl', u+'matomo.php']); _paq.push(['setSiteId', '1']); var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0]; g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s); })(); </script></head><body onload="es.jasper.simpleCalendar.init();" itemscope="itemscope" itemtype="http://schema.org/BlogPosting"><table border="0" cellpadding="0" cellspacing="0"><tr><td width="180" align="center"><a href="/"><img style="border:0;width:135px;height:32px" src="/images/toprowlk.gif" alt="lkml.org" /></a></td><td width="32">聽</td><td class="nb"><div><a class="nb" href="/lkml"> [lkml]</a> 聽 <a class="nb" href="/lkml/2005"> [2005]</a> 聽 <a class="nb" href="/lkml/2005/12"> [Dec]</a> 聽 <a class="nb" href="/lkml/2005/12/14"> [14]</a> 聽 <a class="nb" href="/lkml/last100"> [last100]</a> 聽 <a href="/rss.php"><img src="/images/rss-or.gif" border="0" alt="RSS Feed" /></a></div><div>Views: <a href="#" class="nowrap" onclick="setActiveStyleSheet('wrap');return false;">[wrap]</a><a href="#" class="wrap" onclick="setActiveStyleSheet('nowrap');return false;">[no wrap]</a> 聽 <a class="nb" href="/lkml/mheaders/2005/12/14/298" onclick="this.href='/lkml/headers'+'/2005/12/14/298';">[headers]</a>聽 <a href="/lkml/bounce/2005/12/14/298">[forward]</a>聽 </div></td><td width="32">聽</td></tr><tr><td valign="top"><div class="es-jasper-simpleCalendar" baseurl="/lkml/"></div><div class="threadlist">Messages in this thread</div><ul class="threadlist"><li class="root"><a href="/lkml/2005/12/14/298">First message in thread</a></li><li class="origin"><a href="/lkml/2005/12/14/396">Dinakar Guniguntala</a><ul><li><a href="/lkml/2005/12/14/396">david singleton</a><ul><li><a href="/lkml/2005/12/15/277">Dinakar Guniguntala</a><ul><li><a href="/lkml/2005/12/15/301">David Singleton</a></li><li><a href="/lkml/2005/12/15/380">david singleton</a><ul><li><a href="/lkml/2005/12/16/181">Dinakar Guniguntala</a></li></ul></li></ul></li></ul></li><li><a href="/lkml/2005/12/15/265">David Singleton</a><ul><li><a href="/lkml/2005/12/15/279">Dinakar Guniguntala</a></li><li><a href="/lkml/2005/12/20/60">Ingo Molnar</a><ul><li><a href="/lkml/2005/12/20/95">Dinakar Guniguntala</a><ul><li><a href="/lkml/2005/12/20/133">Esben Nielsen</a></li><li><a href="/lkml/2006/1/2/183">david singleton</a></li><li><a href="/lkml/2006/1/4/502">david singleton</a></li></ul></li></ul></li></ul></li></ul></li></ul><div class="threadlist">Patch in this message</div><ul class="threadlist"><li><a href="/lkml/diff/2005/12/14/298/1">Get diff 1</a></li></ul></td><td width="32" rowspan="2" class="c" valign="top"><img src="/images/icornerl.gif" width="32" height="32" alt="/" /></td><td class="c" rowspan="2" valign="top" style="padding-top: 1em"><table><tr><td><table><tr><td class="lp">Date</td><td class="rp" itemprop="datePublished">Thu, 15 Dec 2005 04:09:13 +0530</td></tr><tr><td class="lp">From</td><td class="rp" itemprop="author">Dinakar Guniguntala <></td></tr><tr><td class="lp">Subject</td><td class="rp" itemprop="name">Recursion bug in -rt</td></tr></table></td><td></td></tr></table><pre itemprop="articleBody">Hi David,<br /><br />I hit this bug with -rt22-rf11<br /><br />==========================================<br />[ BUG: lock recursion deadlock detected! |<br />------------------------------------------<br />already locked: [f7abbc94] {futex}<br />.. held by: testpi-3: 4595 [f7becdd0, 59]<br />... acquired at: futex_wait_robust+0x142/0x1f3<br />------------------------------<br />| showing all locks held by: | (testpi-3/4595 [f7becdd0, 59]):<br />------------------------------<br /><br />#001: [f7abbc94] {futex}<br />... acquired at: futex_wait_robust+0x142/0x1f3<br /><br />-{current task's backtrace}-----------------><br /> [<c0103e04>] dump_stack+0x1e/0x20 (20)<br /> [<c0136bc2>] check_deadlock+0x2d7/0x334 (44)<br /> [<c01379bc>] task_blocks_on_lock+0x2c/0x224 (36)<br /> [<c03f29c5>] __down_interruptible+0x37c/0x95d (160)<br /> [<c013aebf>] down_futex+0xa3/0xe7 (40)<br /> [<c013ebc5>] futex_wait_robust+0x142/0x1f3 (72)<br /> [<c013f35c>] do_futex+0x9a/0x109 (40)<br /> [<c013f4dd>] sys_futex+0x112/0x11e (68)<br /> [<c0102f03>] sysenter_past_esp+0x54/0x75 (-8116)<br />------------------------------<br />| showing all locks held by: | (testpi-3/4595 [f7becdd0, 59]):<br />------------------------------<br /><br />#001: [f7abbc94] {futex}<br />... acquired at: futex_wait_robust+0x142/0x1f3<br /><br />---------------------------------------------------------------------<br /><br />futex.c -> futex_wait_robust<br /><br /> if ((curval & FUTEX_PID) == current->pid) {<br /> ret = -EAGAIN;<br /> goto out_unlock;<br /> }<br /><br />rt.c -> down_futex<br /><br /> if (!owner_task || owner_task == current) {<br /> up(sem);<br /> up_read(&current->mm->mmap_sem);<br /> return -EAGAIN;<br /> }<br /><br />I noticed that both the above checks below have been removed in your<br />patch. I do understand that the futex_wait_robust path has been<br />made similar to the futex_wait path, but I think we are not taking<br />PI into consideration. Basically it looks like we still need to check<br />if the current task has become owner. or are we missing a lock somewhere ?<br /><br />I added the down_futex check above and my test has been<br />running for hours without the oops. Without this check it<br />used to oops within minutes.<br /><br />Patch that works for me attached below. Thoughts?<br /><br /> -Dinakar<br /><br /><br />Index: linux-2.6.14-rt22-rayrt5/kernel/rt.c<br />===================================================================<br />--- linux-2.6.14-rt22-rayrt5.orig/kernel/rt.c 2005-12-15 02:15:13.000000000 +0530<br />+++ linux-2.6.14-rt22-rayrt5/kernel/rt.c 2005-12-15 02:18:29.000000000 +0530<br />@@ -3001,7 +3001,7 @@<br /> * if the owner can't be found return try again.<br /> */<br /> <br />- if (!owner_task) {<br />+ if (!owner_task || owner_task == current) {<br /> up(sem);<br /> up_read(&current->mm->mmap_sem);<br /> return -EAGAIN;</pre></td><td width="32" rowspan="2" class="c" valign="top"><img src="/images/icornerr.gif" width="32" height="32" alt="\" /></td></tr><tr><td align="right" valign="bottom"> 聽 </td></tr><tr><td align="right" valign="bottom">聽</td><td class="c" valign="bottom" style="padding-bottom: 0px"><img src="/images/bcornerl.gif" width="32" height="32" alt="\" /></td><td class="c">聽</td><td class="c" valign="bottom" style="padding-bottom: 0px"><img src="/images/bcornerr.gif" width="32" height="32" alt="/" /></td></tr><tr><td align="right" valign="top" colspan="2"> 聽 </td><td class="lm">Last update: 2005-12-14 23:24 聽聽 [from the cache]<br />漏2003-2020 <a href="http://blog.jasper.es/"><span itemprop="editor">Jasper Spaans</span></a>|hosted at <a href="https://www.digitalocean.com/?refcode=9a8e99d24cf9">Digital Ocean</a> and my Meterkast|<a href="http://blog.jasper.es/categories.html#lkml-ref">Read the blog</a></td><td>聽</td></tr></table><script language="javascript" src="/js/styleswitcher.js" type="text/javascript"></script></body></html>