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href="/lkml/2025/3/8/426">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/8/427">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/8/616">Frederic Weisbecker</a></li><li class="origin"><a href="">"tip-bot2 for Thomas Gleixner"</a></li></ul></li><li><a href="/lkml/2025/3/8/428">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/11/914">Frederic Weisbecker</a><ul><li><a href="/lkml/2025/3/11/977">Thomas Gleixner</a></li></ul></li><li><a href="/lkml/2025/3/13/633">"tip-bot2 for Eric Dumazet"</a></li></ul></li><li><a href="/lkml/2025/3/8/430">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/13/631">"tip-bot2 for Eric Dumazet"</a></li></ul></li><li><a href="/lkml/2025/3/8/431">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/13/630">"tip-bot2 for Thomas Gleixner"</a></li></ul></li><li><a href="/lkml/2025/3/8/432">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/13/632">"tip-bot2 for Thomas Gleixner"</a></li></ul></li><li><a href="/lkml/2025/3/8/433">Thomas Gleixner</a><ul><li><a 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Gleixner</a><ul><li><a href="/lkml/2025/3/11/1110">Frederic Weisbecker</a></li><li><a href="/lkml/2025/3/13/620">"tip-bot2 for Thomas Gleixner"</a></li></ul></li><li><a href="/lkml/2025/3/8/443">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/9/14">Cyrill Gorcunov</a></li><li><a href="/lkml/2025/3/11/1103">Frederic Weisbecker</a></li><li><a href="/lkml/2025/3/13/619">"tip-bot2 for Thomas Gleixner"</a></li></ul></li><li><a href="/lkml/2025/3/8/444">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/9/13">Cyrill Gorcunov</a></li><li><a href="/lkml/2025/3/11/1588">Frederic Weisbecker</a><ul><li><a href="/lkml/2025/3/11/1615">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/11/1618">Thomas Gleixner</a></li></ul></li><li><a href="/lkml/2025/3/12/649">Cyrill Gorcunov</a></li></ul></li></ul></li><li><a href="/lkml/2025/3/8/445">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/10/254">Thomas Gleixner</a><ul><li><a href="/lkml/2025/3/11/1599">Frederic Weisbecker</a></li><li><a href="/lkml/2025/3/13/617">"tip-bot2 for Thomas Gleixner"</a></li></ul></li></ul></li></ul></li></ul><div class="threadlist">Patch in this message</div><ul class="threadlist"><li><a href="/lkml/diff/2025/3/13/634/1">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, 13 Mar 2025 11:31:35 -0000</td></tr><tr><td class="lp">From</td><td class="rp" itemprop="author">"tip-bot2 for Thomas Gleixner" <></td></tr><tr><td class="lp">Subject</td><td class="rp" itemprop="name">[tip: timers/core] posix-timers: Ensure that timer initialization is fully visible</td></tr></table></td><td></td></tr></table><pre itemprop="articleBody">The following commit has been merged into the timers/core branch of tip:<br /><br />Commit-ID: 2389c6efd3ad8edb3bcce0019b4edcc7d9c7de19<br />Gitweb: <a href="https://git.kernel.org/tip/2389c6efd3ad8edb3bcce0019b4edcc7d9c7de19">https://git.kernel.org/tip/2389c6efd3ad8edb3bcce0019b4edcc7d9c7de19</a><br />Author: Thomas Gleixner <tglx@linutronix.de><br />AuthorDate: Sat, 08 Mar 2025 17:48:10 +01:00<br />Committer: Thomas Gleixner <tglx@linutronix.de><br />CommitterDate: Thu, 13 Mar 2025 12:07:16 +01:00<br /><br />posix-timers: Ensure that timer initialization is fully visible<br /><br />Frederic pointed out that the memory operations to initialize the timer are<br />not guaranteed to be visible, when __lock_timer() observes timer::it_signal<br />valid under timer::it_lock:<br /><br /> T0 T1<br /> --------- -----------<br /> do_timer_create()<br /> // A<br /> new_timer->.... = ....<br /> spin_lock(current->sighand)<br /> // B<br /> WRITE_ONCE(new_timer->it_signal, current->signal)<br /> spin_unlock(current->sighand)<br /> sys_timer_*()<br /> t = __lock_timer()<br /> spin_lock(&timr->it_lock)<br /> // observes B<br /> if (timr->it_signal == current->signal)<br /> return timr;<br /> if (!t)<br /> return;<br /> // Is not guaranteed to observe A<br /><br />Protect the write of timer::it_signal, which makes the timer valid, with<br />timer::it_lock as well. This guarantees that T1 must observe the<br />initialization A completely, when it observes the valid signal pointer<br />under timer::it_lock. sighand::siglock must still be taken to protect the<br />signal::posix_timers list.<br /><br />Reported-by: Frederic Weisbecker <frederic@kernel.org><br />Suggested-by: Frederic Weisbecker <frederic@kernel.org><br />Signed-off-by: Thomas Gleixner <tglx@linutronix.de><br />Reviewed-by: Frederic Weisbecker <frederic@kernel.org><br />Link: <a href="https://lore.kernel.org/all/20250308155623.507944489@linutronix.de">https://lore.kernel.org/all/20250308155623.507944489@linutronix.de</a><br /><br />---<br /> kernel/time/posix-timers.c | 21 ++++++++++++++-------<br /> 1 file changed, 14 insertions(+), 7 deletions(-)<br /><br />diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c<br />index 44ba7db..6bf468b 100644<br />--- a/kernel/time/posix-timers.c<br />+++ b/kernel/time/posix-timers.c<br />@@ -462,14 +462,21 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,<br /> if (error)<br /> goto out;<br /> <br />- spin_lock_irq(&current->sighand->siglock);<br />- /* This makes the timer valid in the hash table */<br />- WRITE_ONCE(new_timer->it_signal, current->signal);<br />- hlist_add_head(&new_timer->list, &current->signal->posix_timers);<br />- spin_unlock_irq(&current->sighand->siglock);<br /> /*<br />- * After unlocking sighand::siglock @new_timer is subject to<br />- * concurrent removal and cannot be touched anymore<br />+ * timer::it_lock ensures that __lock_timer() observes a fully<br />+ * initialized timer when it observes a valid timer::it_signal.<br />+ *<br />+ * sighand::siglock is required to protect signal::posix_timers.<br />+ */<br />+ scoped_guard (spinlock_irq, &new_timer->it_lock) {<br />+ guard(spinlock)(&current->sighand->siglock);<br />+ /* This makes the timer valid in the hash table */<br />+ WRITE_ONCE(new_timer->it_signal, current->signal);<br />+ hlist_add_head(&new_timer->list, &current->signal->posix_timers);<br />+ }<br />+ /*<br />+ * After unlocking @new_timer is subject to concurrent removal and<br />+ * cannot be touched anymore<br /> */<br /> return 0;<br /> out:<br /></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: 2025-03-13 12:35 聽聽 [W:0.293 / U:0.027 seconds]<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>