[2/3] PR remote/19496, interrupted syscall in forking-threads-plus-bkpt
Commit Message
This patch addresses "fork:Interrupted system call" (or wait:) failures
in gdb.threads/forking-threads-plus-breakpoint.exp.
The test program spawns ten threads, each of which do ten fork/waitpid
sequences. The cause of the problem was that when one of the fork
children exited before the corresponding fork parent could initiate its
waitpid for that child, a SIGCHLD was delivered and interrupted a fork
or waitpid in another thread.
The fix was to wrap the system calls in a loop to retry the call if
it was interrupted, like:
do
{
pid = fork ();
}
while (pid == -1 && errno == EINTR);
Since this is a Linux-only test I figure it is OK to use errno and EINTR.
Tested on Nios II Linux target with x86 Linux host.
Thanks,
--Don
gdb/testsuite/ChangeLog:
2016-01-27 Don Breazeal <donb@codesourcery.com>
PR remote/19496
* gdb.threads/forking-threads-plus-breakpoint.c (thread_forks):
Retry fork and waitpid on interrupted system call errors.
---
.../gdb.threads/forking-threads-plus-breakpoint.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
Comments
On 01/28/2016 12:48 AM, Don Breazeal wrote:
> This patch addresses "fork:Interrupted system call" (or wait:) failures
> in gdb.threads/forking-threads-plus-breakpoint.exp.
>
> The test program spawns ten threads, each of which do ten fork/waitpid
> sequences. The cause of the problem was that when one of the fork
> children exited before the corresponding fork parent could initiate its
> waitpid for that child, a SIGCHLD was delivered and interrupted a fork
> or waitpid in another thread.
>
> The fix was to wrap the system calls in a loop to retry the call if
> it was interrupted, like:
>
> do
> {
> pid = fork ();
> }
> while (pid == -1 && errno == EINTR);
>
> Since this is a Linux-only test I figure it is OK to use errno and EINTR.
>
> Tested on Nios II Linux target with x86 Linux host.
I'd prefer to avoid this if possible. These loops potentially hide
bugs like ERESTARTSYS escaping out of a syscall and mishandling of
signals. See bc9540e842eb5639ca59cb133adef211d252843c for example:
https://sourceware.org/ml/gdb-patches/2015-02/msg00654.html
How about setting SIGCHLD to SIG_IGN, or making SIGCHLD be SA_RESTART?
Thanks,
Pedro Alves
@@ -22,6 +22,7 @@
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
+#include <errno.h>
/* Number of threads. Each thread continuously spawns a fork and wait
for it. If we have another thread continuously start a step over,
@@ -49,14 +50,23 @@ thread_forks (void *arg)
{
pid_t pid;
- pid = fork ();
+ do
+ {
+ pid = fork ();
+ }
+ while (pid == -1 && errno == EINTR);
if (pid > 0)
{
int status;
/* Parent. */
- pid = waitpid (pid, &status, 0);
+ do
+ {
+ pid = waitpid (pid, &status, 0);
+ }
+ while (pid == -1 && errno == EINTR);
+
if (pid == -1)
{
perror ("wait");