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bpo-32777: Fix _Py_set_inheritable async-safety in subprocess (GH-5560)

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Fix a rare but potential pre-exec child process deadlock in subprocess on POSIX systems when marking file descriptors inheritable on exec in the child process.  This bug appears to have been introduced in 3.4 with the inheritable file descriptors support.

This also changes Python/fileutils.c `set_inheritable` to use the "slow" two `fcntl` syscall path instead of the "fast" single `ioctl` syscall path when asked to be async signal safe (by way of being asked not to raise exceptions).  `ioctl` is not a POSIX async-signal-safe approved function.

ref: http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html
This commit is contained in:
Alexey Izbyshev 2018-02-06 09:09:34 +03:00 • committed by Gregory P. Smith
parent 22864bc8e4
commit c1e46e94de
4 changed files with 26 additions and 7 deletions
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3
Include/fileutils.h
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@ -152,6 +152,9 @@ PyAPI_FUNC(int) _Py_get_inheritable(int fd);
PyAPI_FUNC(int) _Py_set_inheritable(int fd, int inheritable,
int *atomic_flag_works);
PyAPI_FUNC(int) _Py_set_inheritable_async_safe(int fd, int inheritable,
int *atomic_flag_works);
PyAPI_FUNC(int) _Py_dup(int fd);
#ifndef MS_WINDOWS