* defs.h: Add new struct tcb fields: wait_status, next_need_service.

make flags field wider (ints are easier to work with on many CPUs).
* strace.c (trace): Split this function into two:
collect_stopped_tcbs() and handle_stopped_tcbs().
Now we collect *all* waitable tasks, then handle them all,
then repeat.
Fixes RH#478419 "Some threads stop when strace with -f option
is executed on a multi-thread process"
* test/many_looping_threads.c: example program which cna't be straced
successfully without this fix.

diff --git a/ChangeLog b/ChangeLog
index 34c2124412061faa170e31471f2f7cb73c31e204..ac674973b2fc59c7b98cfe370e4fda12b63d5c69 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2009-01-09  Denys Vlasenko  <dvlasenk@redhat.com>
+
+       * defs.h: Add new struct tcb fields: wait_status, next_need_service.
+       make flags field wider (ints are easier to work with on many CPUs).
+       * strace.c (trace): Split this function into two:
+       collect_stopped_tcbs() and handle_stopped_tcbs().
+       Now we collect *all* waitable tasks, then handle them all,
+       then repeat.
+       Fixes RH#478419 "Some threads stop when strace with -f option
+       is executed on a multi-thread process"
+       * test/many_looping_threads.c: example program which cna't be straced
+       successfully without this fix.
+
 2009-01-06  Denys Vlasenko  <dvlasenk@redhat.com>
 
        Output format fixes, improving the situation after recent

diff --git a/defs.h b/defs.h
index 43c31bc971767889bf468f65371892ce068d443d..f9e4ecc967e9cd332b666bde4f64684fec0b5ede 100644 (file)
--- a/defs.h
+++ b/defs.h
@@ -298,8 +298,11 @@ extern int mp_ioctl (int f, int c, void *a, int s);
 
 /* Trace Control Block */
 struct tcb {
-       short flags;            /* See below for TCB_ values */
+       int flags;              /* See below for TCB_ values */
        int pid;                /* Process Id of this entry */
+       int wait_status;        /* Status from last wait() */
+       struct tcb *next_need_service;
+                               /* Linked list of tracees found by wait()s */
        long scno;              /* System call number */
        int u_nargs;            /* System call arguments */
        long u_arg[MAX_ARGS];   /* System call arguments */

diff --git a/strace.c b/strace.c
index ba23b217f59e1e0f9f79dcf7bc9967a57a5917c8..989db1a7f288a59b4b59dad51996b2fcbf6d8b9a 100644 (file)
--- a/strace.c
+++ b/strace.c
@@ -2268,8 +2268,8 @@ handle_group_exit(struct tcb *tcp, int sig)
 }
 #endif
 
-static int
-trace()
+static struct tcb *
+collect_stopped_tcbs(void)
 {
        int pid;
        int wait_errno;
@@ -2277,38 +2277,35 @@ trace()
        struct tcb *tcp;
 #ifdef LINUX
        struct rusage ru;
+       struct rusage* ru_ptr = cflag ? &ru : NULL;
+       int wnohang = 0;
+       struct tcb *found_tcps = NULL;
 #ifdef __WALL
-       static int wait4_options = __WALL;
+       int wait4_options = __WALL;
 #endif
 #endif /* LINUX */
 
-       while (nprocs != 0) {
-               if (interrupted)
-                       return 0;
-               if (interactive)
-                       sigprocmask(SIG_SETMASK, &empty_set, NULL);
+       while (1) {
 #ifdef LINUX
 #ifdef __WALL
-               pid = wait4(-1, &status, wait4_options, cflag ? &ru : NULL);
+               pid = wait4(-1, &status, wait4_options | wnohang, ru_ptr);
                if (pid < 0 && (wait4_options & __WALL) && errno == EINVAL) {
                        /* this kernel does not support __WALL */
                        wait4_options &= ~__WALL;
                        errno = 0;
-                       pid = wait4(-1, &status, wait4_options,
-                                       cflag ? &ru : NULL);
+                       pid = wait4(-1, &status, wait4_options | wnohang, ru_ptr);
                }
                if (pid < 0 && !(wait4_options & __WALL) && errno == ECHILD) {
                        /* most likely a "cloned" process */
-                       pid = wait4(-1, &status, __WCLONE,
-                                       cflag ? &ru : NULL);
-                       if (pid == -1) {
-                               fprintf(stderr, "strace: clone wait4 "
+                       pid = wait4(-1, &status, __WCLONE | wnohang, ru_ptr);
+                       if (pid < 0 && errno != ECHILD) {
+                               fprintf(stderr, "strace: wait4(WCLONE) "
                                                "failed: %s\n", strerror(errno));
                        }
                }
-#else
-               pid = wait4(-1, &status, 0, cflag ? &ru : NULL);
-#endif /* __WALL */
+#else /* !__WALL */
+               pid = wait4(-1, &status, wnohang, ru_ptr);
+#endif
 #endif /* LINUX */
 #ifdef SUNOS4
                pid = wait(&status);
@@ -2317,6 +2314,15 @@ trace()
                if (interactive)
                        sigprocmask(SIG_BLOCK, &blocked_set, NULL);
 
+               if (pid == 0 && wnohang) {
+                       /* We had at least one successful
+                        * wait() before. We waited
+                        * with WNOHANG second time.
+                        * Stop collecting more tracees,
+                        * process what we already have.
+                        */
+                       break;
+               }
                if (pid == -1) {
                        switch (wait_errno) {
                        case EINTR:
@@ -2330,15 +2336,15 @@ trace()
                                 */
 #if 0
                                if (nprocs == 0)
-                                       return 0;
+                                       return NULL;
                                fprintf(stderr, "strace: proc miscount\n");
                                exit(1);
 #endif
-                               return 0;
+                               return NULL;
                        default:
                                errno = wait_errno;
                                perror("strace: wait");
-                               return -1;
+                               exit(1);
                        }
                }
                if (pid == popen_pid) {
@@ -2369,7 +2375,7 @@ trace()
                                        tcp = alloctcb(pid);
                                if (tcp == NULL) {
                                        kill(pid, SIGKILL); /* XXX */
-                                       return 0;
+                                       return NULL;
                                }
                                tcp->flags |= TCB_ATTACHED | TCB_SUSPENDED;
                                if (!qflag)
@@ -2380,7 +2386,7 @@ Process %d attached (waiting for parent)\n",
                        else
                                /* This can happen if a clone call used
                                   CLONE_PTRACE itself.  */
-#endif
+#endif /* LINUX */
                        {
                                fprintf(stderr, "unknown pid: %u\n", pid);
                                if (WIFSTOPPED(status))
@@ -2388,14 +2394,36 @@ Process %d attached (waiting for parent)\n",
                                exit(1);
                        }
                }
-               /* set current output file */
-               outf = tcp->outf;
+
                if (cflag) {
 #ifdef LINUX
                        tv_sub(&tcp->dtime, &ru.ru_stime, &tcp->stime);
                        tcp->stime = ru.ru_stime;
-#endif /* !LINUX */
+#endif
                }
+               tcp->wait_status = status;
+#ifdef LINUX
+               tcp->next_need_service = found_tcps;
+               found_tcps = tcp;
+               wnohang = WNOHANG;
+#endif
+#ifdef SUNOS4
+               /* Probably need to replace wait with waitpid
+                * and loop on Sun too, but I can't test it. Volunteers?
+                */
+               break;
+#endif
+       } /* while (1) - collecting all stopped/exited tracees */
+
+       return tcp;
+}
+
+static int
+handle_stopped_tcbs(struct tcb *tcp)
+{
+       for (; tcp; tcp = tcp->next_need_service) {
+               int pid;
+               int status;
 
                if (tcp->flags & TCB_SUSPENDED) {
                        /*
@@ -2408,6 +2436,11 @@ Process %d attached (waiting for parent)\n",
                         */
                        continue;
                }
+
+               outf = tcp->outf;
+               status = tcp->wait_status;
+               pid = tcp->pid;
+
                if (WIFSIGNALED(status)) {
                        if (pid == strace_child)
                                exit_code = 0x100 | WTERMSIG(status);
@@ -2682,6 +2715,37 @@ Process %d attached (waiting for parent)\n",
                        cleanup();
                        return -1;
                }
+       } /* for each tcp */
+
+       return 0;
+}
+
+static int
+trace()
+{
+       int rc;
+       struct tcb *tcbs;
+
+       while (nprocs != 0) {
+               if (interrupted)
+                       return 0;
+               if (interactive)
+                       sigprocmask(SIG_SETMASK, &empty_set, NULL);
+
+               /* The loop of "wait for one tracee, serve it, repeat"
+                * may leave some tracees never served.
+                * Kernel provides no guarantees of fairness when you have
+                * many waitable tasks.
+                * Try strace -f with test/many_looping_threads.c example.
+                * To fix it, we collect *all* waitable tasks, then handle
+                * them all, then repeat.
+                */
+               tcbs = collect_stopped_tcbs();
+               if (!tcbs)
+                       break;
+               rc = handle_stopped_tcbs(tcbs);
+               if (rc)
+                       return rc;
        }
        return 0;
 }

diff --git a/test/many_looping_threads.c b/test/many_looping_threads.c
new file mode 100644 (file)
index 0000000..d8f7f8d
--- /dev/null
+++ b/test/many_looping_threads.c
@@ -0,0 +1,37 @@
+/* This test is not yet added to Makefile */
+
+#include <stdio.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <signal.h>
+#include <stdlib.h>
+
+static int thd_no;
+
+static void *sub_thd(void *c)
+{
+       fprintf(stderr, "sub-thread %d created\n", ++thd_no);
+       for (;;)
+               getuid();
+       return NULL;
+}
+
+int main(int argc, char **argv)
+{
+       int i;
+       pthread_t *thd;
+       int num_threads = 1;
+
+       if (argv[1])
+               num_threads = atoi(argv[1]);
+
+       thd = malloc(num_threads * sizeof(thd[0]));
+       fprintf(stderr, "test start, num_threads:%d...\n", num_threads);
+       for (i = 0; i < num_threads; i++) {
+               pthread_create(&thd[i], NULL, sub_thd, NULL);
+               fprintf(stderr, "after pthread_create\n");
+       }
+       /* Exit. This kills all threads */
+       return 0;
+}