135 lines
4.0 KiB
Diff
135 lines
4.0 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Martin Wilck <mwilck@suse.com>
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Date: Thu, 17 Dec 2020 16:50:06 +0100
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Subject: [PATCH] multipathd: add code to initalize unwinder
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glibc's implementation of pthread_cancel() loads symbols from
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libgcc_s.so using dlopen() when pthread_cancel() is called
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for the first time. This happens even with LD_BIND_NOW=1.
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This may imply the need for file system access when a thread is
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cancelled, which in the case of multipath-tools might be in a
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dangerous situation where multipathd must avoid blocking.
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Call load_unwinder() during startup to make sure the dynamic
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linker has all necessary symbols resolved early on.
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This implementation simply creates a dummy thread and cancels
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it. This way all necessary symbols for thread cancellation
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will be loaded, no matter what the C library needs to implement
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cancellation.
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Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>
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Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
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---
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multipathd/Makefile | 2 +-
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multipathd/init_unwinder.c | 34 ++++++++++++++++++++++++++++++++++
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multipathd/init_unwinder.h | 21 +++++++++++++++++++++
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multipathd/main.c | 2 ++
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4 files changed, 58 insertions(+), 1 deletion(-)
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create mode 100644 multipathd/init_unwinder.c
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create mode 100644 multipathd/init_unwinder.h
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diff --git a/multipathd/Makefile b/multipathd/Makefile
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index 632b82b1..d053c1ed 100644
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--- a/multipathd/Makefile
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+++ b/multipathd/Makefile
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@@ -30,7 +30,7 @@ ifeq ($(ENABLE_DMEVENTS_POLL),0)
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endif
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OBJS = main.o pidfile.o uxlsnr.o uxclnt.o cli.o cli_handlers.o waiter.o \
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- dmevents.o
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+ dmevents.o init_unwinder.o
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EXEC = multipathd
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diff --git a/multipathd/init_unwinder.c b/multipathd/init_unwinder.c
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new file mode 100644
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index 00000000..14467f3d
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--- /dev/null
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+++ b/multipathd/init_unwinder.c
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@@ -0,0 +1,34 @@
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+#include <pthread.h>
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+#include <unistd.h>
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+#include "init_unwinder.h"
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+
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+static pthread_mutex_t dummy_mtx = PTHREAD_MUTEX_INITIALIZER;
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+static pthread_cond_t dummy_cond = PTHREAD_COND_INITIALIZER;
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+
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+static void *dummy_thread(void *arg __attribute__((unused)))
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+{
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+ pthread_mutex_lock(&dummy_mtx);
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+ pthread_cond_broadcast(&dummy_cond);
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+ pthread_mutex_unlock(&dummy_mtx);
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+ pause();
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+ return NULL;
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+}
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+
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+int init_unwinder(void)
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+{
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+ pthread_t dummy;
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+ int rc;
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+
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+ pthread_mutex_lock(&dummy_mtx);
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+
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+ rc = pthread_create(&dummy, NULL, dummy_thread, NULL);
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+ if (rc != 0) {
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+ pthread_mutex_unlock(&dummy_mtx);
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+ return rc;
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+ }
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+
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+ pthread_cond_wait(&dummy_cond, &dummy_mtx);
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+ pthread_mutex_unlock(&dummy_mtx);
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+
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+ return pthread_cancel(dummy);
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+}
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diff --git a/multipathd/init_unwinder.h b/multipathd/init_unwinder.h
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new file mode 100644
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index 00000000..ada09f82
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--- /dev/null
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+++ b/multipathd/init_unwinder.h
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@@ -0,0 +1,21 @@
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+#ifndef _INIT_UNWINDER_H
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+#define _INIT_UNWINDER_H 1
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+
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+/*
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+ * init_unwinder(): make sure unwinder symbols are loaded
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+ *
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+ * libc's implementation of pthread_cancel() loads symbols from
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+ * libgcc_s.so using dlopen() when pthread_cancel() is called
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+ * for the first time. This happens even with LD_BIND_NOW=1.
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+ * This may imply the need for file system access when a thread is
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+ * cancelled, which in the case of multipath-tools might be in a
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+ * dangerous situation where multipathd must avoid blocking.
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+ *
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+ * Call load_unwinder() during startup to make sure the dynamic
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+ * linker has all necessary symbols resolved early on.
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+ *
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+ * Return: 0 if successful, an error number otherwise.
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+ */
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+int init_unwinder(void);
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+
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+#endif
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diff --git a/multipathd/main.c b/multipathd/main.c
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index 99a89a69..6f851ae8 100644
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--- a/multipathd/main.c
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+++ b/multipathd/main.c
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@@ -83,6 +83,7 @@
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#include "wwids.h"
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#include "foreign.h"
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#include "../third-party/valgrind/drd.h"
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+#include "init_unwinder.h"
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#define FILE_NAME_SIZE 256
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#define CMDSIZE 160
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@@ -3041,6 +3042,7 @@ child (__attribute__((unused)) void *param)
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enum daemon_status state;
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int exit_code = 1;
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+ init_unwinder();
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mlockall(MCL_CURRENT | MCL_FUTURE);
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signal_init();
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mp_rcu_data = setup_rcu();
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--
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2.17.2
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