From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Martin Wilck Date: Wed, 23 Sep 2020 18:02:39 +0200 Subject: [PATCH] multipathd: Fix liburcu memory leak Fix this leak in multipathd, reported by valgrind, that messes up multipathd's otherwise clean leak report: ==23823== 336 bytes in 1 blocks are possibly lost in loss record 3 of 3 ==23823== at 0x483AB65: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==23823== by 0x4012F16: _dl_allocate_tls (in /lib64/ld-2.31.so) ==23823== by 0x493BB8E: pthread_create@@GLIBC_2.2.5 (in /lib64/libpthread-2.31.so) ==23823== by 0x492A9A9: call_rcu_data_init (urcu-call-rcu-impl.h:437) ==23823== by 0x492AD2F: UnknownInlinedFun (urcu-call-rcu-impl.h:492) ==23823== by 0x492AD2F: create_call_rcu_data_memb (urcu-call-rcu-impl.h:504) ==23823== by 0x1164E3: child.constprop.0.isra.0 (main.c:2915) ==23823== by 0x10F50C: main (main.c:3335) ==23823== ==23823== LEAK SUMMARY: ==23823== definitely lost: 0 bytes in 0 blocks ==23823== indirectly lost: 0 bytes in 0 blocks ==23823== possibly lost: 336 bytes in 1 blocks The problem is caused by using liburcu's default RCU call handler, which liburcu refuses to stop/join. See comments in the code. Reviewed-by: Benjamin Marzinski Signed-off-by: Benjamin Marzinski --- multipathd/main.c | 45 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 44 insertions(+), 1 deletion(-) diff --git a/multipathd/main.c b/multipathd/main.c index c5c374b7..ce14bb66 100644 --- a/multipathd/main.c +++ b/multipathd/main.c @@ -2889,6 +2889,48 @@ set_oom_adj (void) condlog(0, "couldn't adjust oom score"); } +/* + * Use a non-default call_rcu_data for child(). + * + * We do this to avoid a memory leak from liburcu. + * liburcu never frees the default rcu handler (see comments on + * call_rcu_data_free() in urcu-call-rcu-impl.h), its thread + * can't be joined with pthread_join(), leaving a memory leak. + * + * Therefore we create our own, which can be destroyed and joined. + */ +static struct call_rcu_data *setup_rcu(void) +{ + struct call_rcu_data *crdp; + + rcu_init(); + rcu_register_thread(); + crdp = create_call_rcu_data(0UL, -1); + if (crdp != NULL) + set_thread_call_rcu_data(crdp); + return crdp; +} + +static struct call_rcu_data *mp_rcu_data; + +static void cleanup_rcu(void) +{ + pthread_t rcu_thread; + + /* Wait for any pending RCU calls */ + rcu_barrier(); + if (mp_rcu_data != NULL) { + rcu_thread = get_call_rcu_thread(mp_rcu_data); + /* detach this thread from the RCU thread */ + set_thread_call_rcu_data(NULL); + synchronize_rcu(); + /* tell RCU thread to exit */ + call_rcu_data_free(mp_rcu_data); + pthread_join(rcu_thread, NULL); + } + rcu_unregister_thread(); +} + static int child (__attribute__((unused)) void *param) { @@ -2906,7 +2948,8 @@ child (__attribute__((unused)) void *param) mlockall(MCL_CURRENT | MCL_FUTURE); signal_init(); - rcu_init(); + mp_rcu_data = setup_rcu(); + atexit(cleanup_rcu); setup_thread_attr(&misc_attr, 64 * 1024, 0); setup_thread_attr(&uevent_attr, DEFAULT_UEVENT_STACKSIZE * 1024, 0); -- 2.17.2