From 830daae1c82ed33deef0086b7b6323e5be0b0cc8 Mon Sep 17 00:00:00 2001
From: Nir Soffer <nirsof@gmail.com>
Date: Thu, 7 Dec 2017 22:25:39 +0200
Subject: [PATCH] [2.7] bpo-32186: Release the GIL during fstat and lseek calls
 (#4651)

In fileio, there were 3 fstat() calls and one lseek() call that did not
release the GIL during the call. This can cause all threads to hang for
unlimited time when using io.FileIO with inaccessible NFS server.

Same issue seen in fileio exists also in fileobject, fixed in the same
way.
---
 .../2017-11-30-20-33-22.bpo-32186.O42bVe.rst  |  4 ++
 Modules/_io/fileio.c                          | 55 +++++++++++++++----
 Objects/fileobject.c                          | 21 ++++++-
 3 files changed, 66 insertions(+), 14 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2017-11-30-20-33-22.bpo-32186.O42bVe.rst

diff --git a/Misc/NEWS.d/next/Library/2017-11-30-20-33-22.bpo-32186.O42bVe.rst b/Misc/NEWS.d/next/Library/2017-11-30-20-33-22.bpo-32186.O42bVe.rst
new file mode 100644
index 0000000000..66c4468e80
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-11-30-20-33-22.bpo-32186.O42bVe.rst
@@ -0,0 +1,4 @@
+Creating io.FileIO() and builtin file() objects now release the GIL when
+checking the file descriptor. io.FileIO.readall(), io.FileIO.read(), and
+file.read() now release the GIL when getting the file size.  Fixed hang of all
+threads with inaccessible NFS server.  Patch by Nir Soffer.
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 4a71a57ec0..2b40ada195 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -146,9 +146,15 @@ dircheck(fileio* self, PyObject *nameobj)
 {
 #if defined(HAVE_FSTAT) && defined(S_IFDIR) && defined(EISDIR)
     struct stat buf;
+    int res;
     if (self->fd < 0)
         return 0;
-    if (fstat(self->fd, &buf) == 0 && S_ISDIR(buf.st_mode)) {
+
+    Py_BEGIN_ALLOW_THREADS
+    res = fstat(self->fd, &buf);
+    Py_END_ALLOW_THREADS
+
+    if (res == 0 && S_ISDIR(buf.st_mode)) {
         errno = EISDIR;
         PyErr_SetFromErrnoWithFilenameObject(PyExc_IOError, nameobj);
         return -1;
@@ -162,17 +168,34 @@ check_fd(int fd)
 {
 #if defined(HAVE_FSTAT)
     struct stat buf;
-    if (!_PyVerify_fd(fd) || (fstat(fd, &buf) < 0 && errno == EBADF)) {
-        PyObject *exc;
-        char *msg = strerror(EBADF);
-        exc = PyObject_CallFunction(PyExc_OSError, "(is)",
-                                    EBADF, msg);
-        PyErr_SetObject(PyExc_OSError, exc);
-        Py_XDECREF(exc);
-        return -1;
+    int res;
+    PyObject *exc;
+    char *msg;
+
+    if (!_PyVerify_fd(fd)) {
+        goto badfd;
     }
-#endif
+
+    Py_BEGIN_ALLOW_THREADS
+    res = fstat(fd, &buf);
+    Py_END_ALLOW_THREADS
+
+    if (res < 0 && errno == EBADF) {
+        goto badfd;
+    }
+
     return 0;
+
+badfd:
+    msg = strerror(EBADF);
+    exc = PyObject_CallFunction(PyExc_OSError, "(is)",
+                                EBADF, msg);
+    PyErr_SetObject(PyExc_OSError, exc);
+    Py_XDECREF(exc);
+    return -1;
+#else
+    return 0;
+#endif
 }
 
 
@@ -519,9 +542,19 @@ new_buffersize(fileio *self, size_t currentsize)
 #ifdef HAVE_FSTAT
     off_t pos, end;
     struct stat st;
-    if (fstat(self->fd, &st) == 0) {
+    int res;
+
+    Py_BEGIN_ALLOW_THREADS
+    res = fstat(self->fd, &st);
+    Py_END_ALLOW_THREADS
+
+    if (res == 0) {
         end = st.st_size;
+
+        Py_BEGIN_ALLOW_THREADS
         pos = lseek(self->fd, 0L, SEEK_CUR);
+        Py_END_ALLOW_THREADS
+
         /* Files claiming a size smaller than SMALLCHUNK may
            actually be streaming pseudo-files. In this case, we
            apply the more aggressive algorithm below.
diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index 2f63c374d1..8d1c5812f0 100644
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -121,10 +121,15 @@ dircheck(PyFileObject* f)
 {
 #if defined(HAVE_FSTAT) && defined(S_IFDIR) && defined(EISDIR)
     struct stat buf;
+    int res;
     if (f->f_fp == NULL)
         return f;
-    if (fstat(fileno(f->f_fp), &buf) == 0 &&
-        S_ISDIR(buf.st_mode)) {
+
+    Py_BEGIN_ALLOW_THREADS
+    res = fstat(fileno(f->f_fp), &buf);
+    Py_END_ALLOW_THREADS
+
+    if (res == 0 && S_ISDIR(buf.st_mode)) {
         char *msg = strerror(EISDIR);
         PyObject *exc = PyObject_CallFunction(PyExc_IOError, "(isO)",
                                               EISDIR, msg, f->f_name);
@@ -1010,7 +1015,13 @@ new_buffersize(PyFileObject *f, size_t currentsize)
 #ifdef HAVE_FSTAT
     off_t pos, end;
     struct stat st;
-    if (fstat(fileno(f->f_fp), &st) == 0) {
+    int res;
+
+    Py_BEGIN_ALLOW_THREADS
+    res = fstat(fileno(f->f_fp), &st);
+    Py_END_ALLOW_THREADS
+
+    if (res == 0) {
         end = st.st_size;
         /* The following is not a bug: we really need to call lseek()
            *and* ftell().  The reason is that some stdio libraries
@@ -1021,7 +1032,11 @@ new_buffersize(PyFileObject *f, size_t currentsize)
            works.  We can't use the lseek() value either, because we
            need to take the amount of buffered data into account.
            (Yet another reason why stdio stinks. :-) */
+
+        Py_BEGIN_ALLOW_THREADS
         pos = lseek(fileno(f->f_fp), 0L, SEEK_CUR);
+        Py_END_ALLOW_THREADS
+
         if (pos >= 0) {
             pos = ftell(f->f_fp);
         }
-- 
2.50.1