| From ce240a1124a5b8d09263a7fa853bf575ec0565c0 Mon Sep 17 00:00:00 2001 |
| From: Adrian Ratiu <adrian.ratiu@collabora.com> |
| Date: Fri, 9 Jul 2021 11:49:23 +0300 |
| Subject: [PATCH] nptl: mitigate failed pthread_cond_signal wakeup |
| |
| This mitigation is applied until the bug reported at [1] |
| gets a proper fix in glibc upstream. Work is on-going and |
| the proposed fixes are more complex than this mitigation, |
| so for now use it to avoid the deadlock because it safest. |
| |
| The mitigation is at location [2] in the above bug report |
| and was also tested and deployed in Ubuntu starting with |
| Bionic onward [3]. |
| |
| [1] https://sourceware.org/bugzilla/show_bug.cgi?id=25847 |
| [2] https://sourceware.org/bugzilla/attachment.cgi?id=12484 |
| [3] https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1899800 |
| |
| Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> |
| --- |
| nptl/pthread_cond_wait.c | 9 +++++++++ |
| 1 file changed, 9 insertions(+) |
| |
| diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c |
| index 85ddbc1011..28ef330ac2 100644 |
| --- a/nptl/pthread_cond_wait.c |
| +++ b/nptl/pthread_cond_wait.c |
| @@ -608,6 +608,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex, |
| the signal from, which cause it to block using the |
| futex). */ |
| futex_wake (cond->__data.__g_signals + g, 1, private); |
| + |
| + /* We might be wrong about stealing, we got the signal |
| + from the an old g1, but ended up returning it to |
| + a different g1. We can't tell whether it is the case. |
| + If it is, we now caused another issue: |
| + now g_refs[g1] is one less than g_size[g1]. |
| + The mitigation step is to broadcast g1 and g2, let every |
| + waiter wake up spuriosly. */ |
| + __pthread_cond_broadcast(cond); |
| break; |
| } |
| /* TODO Back off. */ |
| -- |
| 2.32.0 |
| |
