From: Paul Mackerras <paulus@ozlabs.org>
Date: Fri, 9 Sep 2022 02:07:20 +0000 (+1000)
Subject: Merge pull request #366 from pali/rtnetlink-register
X-Git-Tag: ppp-2.5.0~24
X-Git-Url: http://git.ozlabs.org/?p=ppp.git;a=commitdiff_plain;h=35198adc7f3c1f0c1e3437f983e7f3ac96477997;hp=a14ede90df712b4a0fed82b9a66a81c56e1e97a9

Merge pull request #366 from pali/rtnetlink-register

pppd: Retry registering interface when on rtnetlink -EBUSY error
---

diff --git a/pppd/sys-linux.c b/pppd/sys-linux.c
index dc3b4d6..7beb977 100644
--- a/pppd/sys-linux.c
+++ b/pppd/sys-linux.c
@@ -864,7 +864,14 @@ static int make_ppp_unit_rtnetlink(void)
     nlreq.ifli.ifid.ifdata[0].rta.rta_type = IFLA_PPP_DEV_FD;
     nlreq.ifli.ifid.ifdata[0].ppp.ppp_dev_fd = ppp_dev_fd;
 
-    resp = rtnetlink_msg("RTM_NEWLINK/NLM_F_CREATE", NULL, &nlreq, sizeof(nlreq), NULL, NULL, 0);
+    /*
+     * See kernel function ppp_nl_newlink(), which may return -EBUSY to prevent
+     * possible deadlock in kernel and ask userspace to retry request again.
+     */
+    do {
+        resp = rtnetlink_msg("RTM_NEWLINK/NLM_F_CREATE", NULL, &nlreq, sizeof(nlreq), NULL, NULL, 0);
+    } while (resp == -EBUSY);
+
     if (resp) {
         /*
          * Linux kernel versions prior to 4.7 do not support creating ppp