From 669ff911e2571f74a2668493e326ac9a505776bd Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Fri, 8 Feb 2019 12:46:19 +0100 Subject: nptl: Avoid fork handler lock for async-signal-safe fork [BZ #24161] Commit 27761a1042daf01987e7d79636d0c41511c6df3c ("Refactor atfork handlers") introduced a lock, atfork_lock, around fork handler list accesses. It turns out that this lock occasionally results in self-deadlocks in malloc/tst-mallocfork2: (gdb) bt #0 __lll_lock_wait_private () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:63 #1 0x00007f160c6f927a in __run_fork_handlers (who=(unknown: 209394016), who@entry=atfork_run_prepare) at register-atfork.c:116 #2 0x00007f160c6b7897 in __libc_fork () at ../sysdeps/nptl/fork.c:58 #3 0x00000000004027d6 in sigusr1_handler (signo=) at tst-mallocfork2.c:80 #4 sigusr1_handler (signo=) at tst-mallocfork2.c:64 #5 #6 0x00007f160c6f92e4 in __run_fork_handlers (who=who@entry=atfork_run_parent) at register-atfork.c:136 #7 0x00007f160c6b79a2 in __libc_fork () at ../sysdeps/nptl/fork.c:152 #8 0x0000000000402567 in do_test () at tst-mallocfork2.c:156 #9 0x0000000000402dd2 in support_test_main (argc=1, argv=0x7ffc81ef1ab0, config=config@entry=0x7ffc81ef1970) at support_test_main.c:350 #10 0x0000000000402362 in main (argc=, argv=) at ../support/test-driver.c:168 If no locking happens in the single-threaded case (where fork is expected to be async-signal-safe), this deadlock is avoided. (pthread_atfork is not required to be async-signal-safe, so a fork call from a signal handler interrupting pthread_atfork is not a problem.) --- nptl/register-atfork.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'nptl/register-atfork.c') diff --git a/nptl/register-atfork.c b/nptl/register-atfork.c index bc797b761a..80a1becb5f 100644 --- a/nptl/register-atfork.c +++ b/nptl/register-atfork.c @@ -107,13 +107,14 @@ __unregister_atfork (void *dso_handle) } void -__run_fork_handlers (enum __run_fork_handler_type who) +__run_fork_handlers (enum __run_fork_handler_type who, _Bool do_locking) { struct fork_handler *runp; if (who == atfork_run_prepare) { - lll_lock (atfork_lock, LLL_PRIVATE); + if (do_locking) + lll_lock (atfork_lock, LLL_PRIVATE); size_t sl = fork_handler_list_size (&fork_handlers); for (size_t i = sl; i > 0; i--) { @@ -133,7 +134,8 @@ __run_fork_handlers (enum __run_fork_handler_type who) else if (who == atfork_run_parent && runp->parent_handler) runp->parent_handler (); } - lll_unlock (atfork_lock, LLL_PRIVATE); + if (do_locking) + lll_unlock (atfork_lock, LLL_PRIVATE); } } -- cgit v1.2.3