python · nirs · Mar 7, 2018 · Mar 11, 2018
diff --git a/Misc/NEWS.d/next/Library/2018-03-12-00-36-37.bpo-33021.fBmBwP.rst b/Misc/NEWS.d/next/Library/2018-03-12-00-36-37.bpo-33021.fBmBwP.rst
@@ -0,0 +1,4 @@
+Release the GIL during fstat() calls, avoiding hang of all threads when
+calling imp.load_dynamic(), imp.load_source(), mmap.mmap(),
+mmapobject.size(), os.fdopen(), os.urandom(), and random.seed().  Patch by
+Nir Soffer.
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
@@ -415,7 +415,13 @@ mmap_size_method(mmap_object *self,
 #ifdef UNIX
     {
         struct stat buf;
-        if (-1 == fstat(self->fd, &buf)) {
+        int res;
+
+        Py_BEGIN_ALLOW_THREADS
+        res = fstat(self->fd, &buf);
+        Py_END_ALLOW_THREADS
+
+        if (-1 == res) {
             PyErr_SetFromErrno(mmap_module_error);
             return NULL;
         }
@@ -1097,6 +1103,7 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
 {
 #ifdef HAVE_FSTAT
     struct stat st;
+    int fstat_result;
 #endif
     mmap_object *m_obj;
     Py_ssize_t map_size;
@@ -1170,7 +1177,14 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
         fsync(fd);
     }
 #  endif
-    if (fd != -1 && fstat(fd, &st) == 0 && S_ISREG(st.st_mode)) {
+
+    if (fd != -1) {
+        Py_BEGIN_ALLOW_THREADS
+        fstat_result = fstat(fd, &st);
+        Py_END_ALLOW_THREADS
+    }
+
+    if (fd != -1 && fstat_result == 0 && S_ISREG(st.st_mode)) {
         if (map_size == 0) {
             if (st.st_size == 0) {
                 PyErr_SetString(PyExc_ValueError,

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -6920,7 +6920,13 @@ posix_fdopen(PyObject *self, PyObject *args)
         struct stat buf;
         const char *msg;
         PyObject *exc;
-        if (fstat(fd, &buf) == 0 && S_ISDIR(buf.st_mode)) {
+        int res;
+
+        Py_BEGIN_ALLOW_THREADS
+        res = fstat(fd, &buf);
+        Py_END_ALLOW_THREADS
+
+        if (res == 0 && S_ISDIR(buf.st_mode)) {
             PyMem_FREE(mode);
             msg = strerror(EISDIR);
             exc = PyObject_CallFunction(PyExc_IOError, "(iss)",

diff --git a/Python/dynload_shlib.c b/Python/dynload_shlib.c
@@ -87,7 +87,11 @@ dl_funcptr _PyImport_GetDynLoadFunc(const char *fqname, const char *shortname,
     if (fp != NULL) {
         int i;
         struct stat statb;
+
+        Py_BEGIN_ALLOW_THREADS
         fstat(fileno(fp), &statb);
+        Py_END_ALLOW_THREADS
+
         for (i = 0; i < nhandles; i++) {
             if (statb.st_dev == handles[i].dev &&
                 statb.st_ino == handles[i].ino) {

diff --git a/Python/import.c b/Python/import.c
@@ -1054,14 +1054,19 @@ static PyObject *
 load_source_module(char *name, char *pathname, FILE *fp)
 {
     struct stat st;
+    int fstat_result;
     FILE *fpc;
     char *buf;
     char *cpathname;
     PyCodeObject *co = NULL;
     PyObject *m;
     time_t mtime;
 
-    if (fstat(fileno(fp), &st) != 0) {
+    Py_BEGIN_ALLOW_THREADS
+    fstat_result = fstat(fileno(fp), &st);
+    Py_END_ALLOW_THREADS
+
+    if (fstat_result != 0) {
         PyErr_Format(PyExc_RuntimeError,
                      "unable to get file status from '%s'",
                      pathname);

diff --git a/Python/random.c b/Python/random.c
@@ -210,14 +210,18 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
     int fd;
     Py_ssize_t n;
     struct stat st;
+    int fstat_result;
     int attr;
 
     if (size <= 0)
         return 0;
 
     if (urandom_cache.fd >= 0) {
         /* Does the fd point to the same thing as before? (issue #21207) */
-        if (fstat(urandom_cache.fd, &st)
+        Py_BEGIN_ALLOW_THREADS
+        fstat_result = fstat(urandom_cache.fd, &st);
+        Py_END_ALLOW_THREADS
+        if (fstat_result
             || st.st_dev != urandom_cache.st_dev
             || st.st_ino != urandom_cache.st_ino) {
             /* Something changed: forget the cached fd (but don't close it,
@@ -257,7 +261,10 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
             fd = urandom_cache.fd;
         }
         else {
-            if (fstat(fd, &st)) {
+            Py_BEGIN_ALLOW_THREADS
+            fstat_result = fstat(fd, &st);
+            Py_END_ALLOW_THREADS
+            if (fstat_result) {
                 PyErr_SetFromErrno(PyExc_OSError);
                 close(fd);
                 return -1;