From 94225ab4bcc1613531558a632270b5edce779bc9 Mon Sep 17 00:00:00 2001
From: Khem Raj <raj.khem@gmail.com>
Date: Sat, 27 Jan 2018 10:08:04 -0800
Subject: [PATCH 27/27] Acquire ld.so lock before switching to malloc_atfork

The patch is from
  https://sourceware.org/bugzilla/show_bug.cgi?id=4578

If a thread happens to hold dl_load_lock and have r_state set to RT_ADD or
RT_DELETE at the time another thread calls fork(), then the child exit code
from fork (in nptl/sysdeps/unix/sysv/linux/fork.c in our case) re-initializes
dl_load_lock but does not restore r_state to RT_CONSISTENT. If the child
subsequently requires ld.so functionality before calling exec(), then the
assertion will fire.

The patch acquires dl_load_lock on entry to fork() and releases it on exit
from the parent path.  The child path is initialized as currently done.
This is essentially pthreads_atfork, but forced to be first because the
acquisition of dl_load_lock must happen before malloc_atfork is active
to avoid a deadlock.

The patch has not yet been integrated upstream.

Upstream-Status: Pending [ Not Author See bugzilla]

Signed-off-by: Raghunath Lolur <Raghunath.Lolur@kpit.com>
Signed-off-by: Yuanjie Huang <yuanjie.huang@windriver.com>
Signed-off-by: Zhixiong Chi <zhixiong.chi@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
---
 sysdeps/nptl/fork.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sysdeps/nptl/fork.c b/sysdeps/nptl/fork.c
index f87506f398..225e7b51f8 100644
--- a/sysdeps/nptl/fork.c
+++ b/sysdeps/nptl/fork.c
@@ -25,6 +25,7 @@
 #include <tls.h>
 #include <hp-timing.h>
 #include <ldsodefs.h>
+#include <libc-lock.h>
 #include <stdio-lock.h>
 #include <atomic.h>
 #include <nptl/pthreadP.h>
@@ -60,6 +61,10 @@ __libc_fork (void)
      but our current fork implementation is not.  */
   bool multiple_threads = THREAD_GETMEM (THREAD_SELF, header.multiple_threads);
 
+  /* grab ld.so lock BEFORE switching to malloc_atfork */
+  __rtld_lock_lock_recursive (GL(dl_load_lock));
+  __rtld_lock_lock_recursive (GL(dl_load_write_lock));
+
   /* Run all the registered preparation handlers.  In reverse order.
      While doing this we build up a list of all the entries.  */
   struct fork_handler *runp;
@@ -246,6 +251,10 @@ __libc_fork (void)
 
 	  allp = allp->next;
 	}
+
+      /* unlock ld.so last, because we locked it first */
+      __rtld_lock_unlock_recursive (GL(dl_load_write_lock));
+      __rtld_lock_unlock_recursive (GL(dl_load_lock));
     }
 
   return pid;
-- 
2.16.1