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gh-104372: Drop the GIL around the vfork() call. #104782

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Merged
gpshead merged 5 commits into from
May 25, 2023
Merged

gh-104372: Drop the GIL around the vfork() call. #104782

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2d54d8e
gh-104372: Drop the GIL around the vfork() call.
gpshead May 23, 2023
eb38573
Simplify: avoid -Wclobbered the compiler warning.
gpshead May 24, 2023
9197a4f
Docs: clarify that timeout= can't cover process creation.
gpshead May 24, 2023
02a8538
Merge branch 'main' into subprocess-drop-gil-before-vfork
gpshead May 24, 2023
df7f7ab
update the comment
gpshead May 25, 2023
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Simplify: avoid -Wclobbered the compiler warning. 
Don't write to the vfork_tstate_save pointer local after vfork.
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@gpshead
gpshead committed May 24, 2023
commit eb385733ce276040999187f711a6520e2578c828
15 changes: 6 additions & 9 deletions Modules/_posixsubprocess.c
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Original file line number Diff line number Diff line change
Expand Up @@ -798,7 +798,7 @@ do_fork_exec(char *const exec_array[],
pid_t pid;

#ifdef VFORK_USABLE
PyThreadState *vfork_tstate_save = NULL;
PyThreadState *vfork_tstate_save;
if (child_sigmask) {
/* These are checked by our caller; verify them in debug builds. */
assert(uid == (uid_t)-1);
Expand All @@ -808,7 +808,7 @@ do_fork_exec(char *const exec_array[],

/* Drop the GIL so that other threads can continue execution while this
* thread in the parent remains blocked per vfork-semantics on the
* child's exec syscall outcome. Exec requires filesystem access which
* child's exec syscall outcome. Exec does filesystem access which
* can take an arbitrarily long time. This addresses GH-104372.
*
* The vfork'ed child still runs in our address space. Per POSIX it
Expand All @@ -817,9 +817,11 @@ do_fork_exec(char *const exec_array[],
*/
vfork_tstate_save = PyEval_SaveThread();
pid = vfork();
if (pid == (pid_t)-1) {
if (pid != 0) {
// Not in the child process, reacquire the GIL.
PyEval_RestoreThread(vfork_tstate_save);
vfork_tstate_save = NULL;
}
if (pid == (pid_t)-1) {
/* If vfork() fails, fall back to using fork(). When it isn't
* allowed in a process by the kernel, vfork can return -1
* with errno EINVAL. https://bugs.python.org/issue47151. */
Expand All @@ -833,11 +835,6 @@ do_fork_exec(char *const exec_array[],

if (pid != 0) {
// Parent process.
#ifdef VFORK_USABLE
if (vfork_tstate_save != NULL) {
PyEval_RestoreThread(vfork_tstate_save);
}
#endif
return pid;
}

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