On Fri, Aug 17, 2007 at 11:41:20AM -0400, John Blackwood wrote:
> Hi Neil,
>
> We've been having problems with this select patch change.
>
> Specifically -- previously, when a ptrace attach was done to a task
> blocked in a select() call and that task had a timeout value,
> the task would restart the select() call with an updated timeout value.
>
> With this patch in place, the task now instead returns EINTR.
>
> A test that shows this issue is provided below.
>
> We also confirmed that attaching to a program sitting
> in select() with gdb makes the select get an EINTR, so this
> behavior also shows up in gdb.
>
> Thank you for your considerations in this matter.
>
I'm on vacation at the moment, but will look at this more closely when I get
back on tuesday
Regards
Neil
> ------------------- -------------------
> #include <stdio.h>
> #include <sys/time.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <errno.h>
> #include <stdlib.h>
> #include <string.h>
> #include <ctype.h>
> #include <time.h>
> #include <signal.h>
> #include <sys/wait.h>
> #include <sys/ptrace.h>
>
> int
> main(int argc, char ** argv) {
> pid_t kid;
> if ((kid = fork()) == 0) {
> int ms_wait = 2000;
> int rval;
> struct timeval timeout;
>
> timeout.tv_sec = ms_wait / 1000;
> timeout.tv_usec = (ms_wait % 1000) * 1000;
> rval = select(0, NULL, NULL, NULL, &timeout);
> if (rval == -1) {
> int errcode = errno;
> printf("Hey! Why did my select error off with errno %d (%s)?\n",
> errcode, strerror(errcode));
> fflush(stdout);
> } else {
> printf("select call completed, return value: %d\n", rval);
> }
> exit(0);
> } else if (kid == (pid_t)-1) {
> perror("fork");
> } else {
> int ms_wait = 500;
> int rval;
> struct timeval timeout;
>
> /* Wait a bit to make sure kid has a chance to get into its
> * select call
> */
> timeout.tv_sec = ms_wait / 1000;
> timeout.tv_usec = (ms_wait % 1000) * 1000;
> rval = select(0, NULL, NULL, NULL, &timeout);
>
> /* Now attach to the kid, then continue him.
> */
> if (ptrace(PTRACE_ATTACH, kid, (void *)0, (void *)0) != 0) {
> perror("ptrace");
> }
> if (waitpid(kid, &rval, 0) != kid) {
> perror("waitpid");
> }
> if (ptrace(PTRACE_CONT, kid, (void *)0, (void *)0) != 0) {
> perror("ptrace");
> }
> if (waitpid(kid, &rval, 0) != kid) {
> perror("waitpid");
> }
> }
> return 0;
> }
--
/***************************************************
*Neil Horman
*Software Engineer
*Red Hat, Inc.
*nhorman@xxxxxxxxxxxxx
*gpg keyid: 1024D / 0x92A74FA1
*http://pgp.mit.edu
***************************************************/
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