From 6ea962e0946da7564a774b08dd3eda28d64e9e56 Mon Sep 17 00:00:00 2001 From: Khem Raj Date: Sat, 27 Jan 2018 10:08:04 -0800 Subject: [PATCH] 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 Signed-off-by: Yuanjie Huang Signed-off-by: Zhixiong Chi Signed-off-by: Khem Raj --- sysdeps/nptl/fork.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/sysdeps/nptl/fork.c b/sysdeps/nptl/fork.c index 0f48933ff1..eef3f9669b 100644 --- a/sysdeps/nptl/fork.c +++ b/sysdeps/nptl/fork.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include #include @@ -56,6 +57,9 @@ __libc_fork (void) bool multiple_threads = THREAD_GETMEM (THREAD_SELF, header.multiple_threads); __run_fork_handlers (atfork_run_prepare); + /* 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)); /* If we are not running multiple threads, we do not have to preserve lock state. If fork runs from a signal handler, only @@ -150,6 +154,9 @@ __libc_fork (void) /* Run the handlers registered for the parent. */ __run_fork_handlers (atfork_run_parent); + /* 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;