diff --git a/Documentation/security/credentials.rst b/Documentation/security/credentials.rst
index 282e79f..c98e0a8 100644
--- a/Documentation/security/credentials.rst
+++ b/Documentation/security/credentials.rst
@@ -437,9 +437,13 @@ new set of credentials by calling::
 
 	struct cred *prepare_creds(void);
 
-this locks current->cred_replace_mutex and then allocates and constructs a
-duplicate of the current process's credentials, returning with the mutex still
-held if successful.  It returns NULL if not successful (out of memory).
+this allocates and constructs a duplicate of the current process's credentials.
+It returns NULL if not successful (out of memory).
+
+If called from __do_execve_file, the mutex current->signal->cred_guard_mutex
+is acquired before this function gets called, and the mutex
+current->signal->cred_change_mutex is acquired later, while the credentials
+and the process mmap are actually changed.
 
 The mutex prevents ``ptrace()`` from altering the ptrace state of a process
 while security checks on credentials construction and changing is taking place
@@ -466,9 +470,8 @@ by calling::
 
 This will alter various aspects of the credentials and the process, giving the
 LSM a chance to do likewise, then it will use ``rcu_assign_pointer()`` to
-actually commit the new credentials to ``current->cred``, it will release
-``current->cred_replace_mutex`` to allow ``ptrace()`` to take place, and it
-will notify the scheduler and others of the changes.
+actually commit the new credentials to ``current->cred``, and it will notify
+the scheduler and others of the changes.
 
 This function is guaranteed to return 0, so that it can be tail-called at the
 end of such functions as ``sys_setresuid()``.
@@ -486,8 +489,7 @@ invoked::
 
 	void abort_creds(struct cred *new);
 
-This releases the lock on ``current->cred_replace_mutex`` that
-``prepare_creds()`` got and then releases the new credentials.
+This releases the new credentials.
 
 
 A typical credentials alteration function would look something like this::
diff --git a/fs/exec.c b/fs/exec.c
index 74d88da..a6884e4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1266,6 +1266,12 @@ int flush_old_exec(struct linux_binprm * bprm)
 	if (retval)
 		goto out;
 
+	retval = mutex_lock_killable(&current->signal->cred_change_mutex);
+	if (retval)
+		goto out;
+
+	bprm->called_flush_old_exec = 1;
+
 	/*
 	 * Must be called _before_ exec_mmap() as bprm->mm is
 	 * not visibile until then. This also enables the update
@@ -1420,6 +1426,8 @@ static void free_bprm(struct linux_binprm *bprm)
 {
 	free_arg_pages(bprm);
 	if (bprm->cred) {
+		if (bprm->called_flush_old_exec)
+			mutex_unlock(&current->signal->cred_change_mutex);
 		mutex_unlock(&current->signal->cred_guard_mutex);
 		abort_creds(bprm->cred);
 	}
@@ -1469,6 +1477,7 @@ void install_exec_creds(struct linux_binprm *bprm)
 	 * credentials; any time after this it may be unlocked.
 	 */
 	security_bprm_committed_creds(bprm);
+	mutex_unlock(&current->signal->cred_change_mutex);
 	mutex_unlock(&current->signal->cred_guard_mutex);
 }
 EXPORT_SYMBOL(install_exec_creds);
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index b40fc63..2e1318b 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -44,7 +44,11 @@ struct linux_binprm {
 		 * exec has happened. Used to sanitize execution environment
 		 * and to set AT_SECURE auxv for glibc.
 		 */
-		secureexec:1;
+		secureexec:1,
+		/*
+		 * Set by flush_old_exec, when the cred_change_mutex is taken.
+		 */
+		called_flush_old_exec:1;
 #ifdef __alpha__
 	unsigned int taso:1;
 #endif
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 8805025..37eeabe 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -225,6 +225,7 @@ struct signal_struct {
 	struct mutex cred_guard_mutex;	/* guard against foreign influences on
 					 * credential calculations
 					 * (notably. ptrace) */
+	struct mutex cred_change_mutex; /* guard against credentials change */
 } __randomize_layout;
 
 /*
diff --git a/init/init_task.c b/init/init_task.c
index 9e5cbe5..6cd9a0f 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -26,6 +26,7 @@
 	.multiprocess	= HLIST_HEAD_INIT,
 	.rlim		= INIT_RLIMITS,
 	.cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex),
+	.cred_change_mutex = __MUTEX_INITIALIZER(init_signals.cred_change_mutex),
 #ifdef CONFIG_POSIX_TIMERS
 	.posix_timers = LIST_HEAD_INIT(init_signals.posix_timers),
 	.cputimer	= {
diff --git a/kernel/cred.c b/kernel/cred.c
index 809a985..e4c78de 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -676,7 +676,7 @@ void __init cred_init(void)
  *
  * Returns the new credentials or NULL if out of memory.
  *
- * Does not take, and does not return holding current->cred_replace_mutex.
+ * Does not take, and does not return holding ->cred_guard_mutex.
  */
 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 {
diff --git a/kernel/fork.c b/kernel/fork.c
index 0808095..0395154 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1224,7 +1224,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 	struct mm_struct *mm;
 	int err;
 
-	err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
+	err =  mutex_lock_killable(&task->signal->cred_change_mutex);
 	if (err)
 		return ERR_PTR(err);
 
@@ -1234,7 +1234,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 		mmput(mm);
 		mm = ERR_PTR(-EACCES);
 	}
-	mutex_unlock(&task->signal->cred_guard_mutex);
+	mutex_unlock(&task->signal->cred_change_mutex);
 
 	return mm;
 }
@@ -1594,6 +1594,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
 
 	mutex_init(&sig->cred_guard_mutex);
+	mutex_init(&sig->cred_change_mutex);
 
 	return 0;
 }
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 357aa7b..b3e6eb5 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -204,7 +204,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 	if (!mm || IS_ERR(mm)) {
 		rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 		/*
-		 * Explicitly map EACCES to EPERM as EPERM is a more a
+		 * Explicitly map EACCES to EPERM as EPERM is a more
 		 * appropriate error code for process_vw_readv/writev
 		 */
 		if (rc == -EACCES)
diff --git a/tools/testing/selftests/ptrace/Makefile b/tools/testing/selftests/ptrace/Makefile
index c0b7f89..2f1f532 100644
--- a/tools/testing/selftests/ptrace/Makefile
+++ b/tools/testing/selftests/ptrace/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
-CFLAGS += -iquote../../../../include/uapi -Wall
+CFLAGS += -std=c99 -pthread -iquote../../../../include/uapi -Wall
 
-TEST_GEN_PROGS := get_syscall_info peeksiginfo
+TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess
 
 include ../lib.mk
diff --git a/tools/testing/selftests/ptrace/vmaccess.c b/tools/testing/selftests/ptrace/vmaccess.c
new file mode 100644
index 0000000..ef08c9f
--- /dev/null
+++ b/tools/testing/selftests/ptrace/vmaccess.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2020 Bernd Edlinger <bernd.edlinger@hotmail.de>
+ * All rights reserved.
+ *
+ * Check whether /proc/$pid/mem can be accessed without causing deadlocks
+ * when de_thread is blocked with ->cred_guard_mutex held.
+ */
+
+#include "../kselftest_harness.h"
+#include <stdio.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/ptrace.h>
+
+static void *thread(void *arg)
+{
+	ptrace(PTRACE_TRACEME, 0, 0, 0);
+	return NULL;
+}
+
+TEST(vmaccess)
+{
+	int f, pid = fork();
+	char mm[64];
+
+	if (!pid) {
+		pthread_t pt;
+		pthread_create(&pt, NULL, thread, NULL);
+		pthread_join(pt, NULL);
+		execlp("true", "true", NULL);
+	}
+
+	sleep(1);
+	sprintf(mm, "/proc/%d/mem", pid);
+	f = open(mm, O_RDONLY);
+	ASSERT_LE(0, f)
+		close(f);
+	/* this is not fixed! ptrace(PTRACE_ATTACH, pid, 0,0); */
+	f = kill(pid, SIGCONT);
+	ASSERT_EQ(0, f);
+}
+
+TEST_HARNESS_MAIN
