When trace-cmd runs a command, specified with the "-F" flag, it forks a
child process and executes the command in its context. This child process
receives a full copy of the parents memory at the moment of fork(). When
it modifies this copy, the parent memory is not affected. Calling the
function update_task_filter() in the child context will operate on a valid
data, but will not update anything in the parent's databases.
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
---
tracecmd/trace-record.c | 64 +++++++++++++++++++++++++++++++++--------
1 file changed, 52 insertions(+), 12 deletions(-)
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 1e4d38fa..ae8a5745 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -11,6 +11,7 @@
#include <stdarg.h>
#include <getopt.h>
#include <time.h>
+#include <semaphore.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
@@ -1187,10 +1188,12 @@ static void get_filter_pid_maps(void)
}
}
-static void update_task_filter(void)
+static void update_task_filter(int pid)
{
struct buffer_instance *instance;
- int pid = getpid();
+
+ if (pid < 0)
+ pid = getpid();
if (no_filter)
return;
@@ -1487,18 +1490,40 @@ static int change_user(const char *user)
return 0;
}
+#define TRACE_RUN_SEM "trace_cmd_semaphore_run"
+#define TRACE_INIT_SEM "trace_cmd_semaphore_init"
static void run_cmd(enum trace_type type, const char *user, int argc, char **argv)
{
+ sem_t *sem_init = SEM_FAILED;
+ sem_t *sem_run = SEM_FAILED;
+ char *die_log = NULL;
int status;
int pid;
- if ((pid = fork()) < 0)
- die("failed to fork");
+ sem_init = sem_open(TRACE_INIT_SEM, O_CREAT, S_IRUSR|S_IWUSR, 0);
+ if (sem_init == SEM_FAILED) {
+ die_log = "failed to init trace_cmd init semaphore";
+ goto out;
+ }
+
+ sem_run = sem_open(TRACE_RUN_SEM, O_CREAT, S_IRUSR|S_IWUSR, 0);
+ if (sem_run == SEM_FAILED) {
+ die_log = "failed to init trace_cmd run semaphore";
+ goto out;
+
+ }
+
+ if ((pid = fork()) < 0) {
+ die_log = "failed to fork";
+ goto out;
+ }
if (!pid) {
/* child */
- update_task_filter();
+ sem_wait(sem_init);
tracecmd_enable_tracing();
enable_ptrace();
+ sem_post(sem_run);
+
/*
* If we are using stderr for stdout, switch
* it back to the saved stdout for the code we run.
@@ -1519,12 +1544,27 @@ static void run_cmd(enum trace_type type, const char *user, int argc, char **arg
die("Failed to exec %s", argv[0]);
}
}
- if (do_ptrace) {
- add_filter_pid(pid, 0);
- ptrace_attach(pid);
+ update_task_filter(pid);
+ sem_post(sem_init);
+ sem_wait(sem_run);
+
+ if (do_ptrace)
ptrace_wait(type);
- } else
+ else
trace_waitpid(type, pid, &status, 0);
+
+out:
+ if (sem_init != SEM_FAILED) {
+ sem_close(sem_init);
+ sem_unlink(TRACE_INIT_SEM);
+ }
+ if (sem_run != SEM_FAILED) {
+ sem_close(sem_run);
+ sem_unlink(TRACE_RUN_SEM);
+ }
+
+ if (die_log)
+ die(die_log);
}
static void
@@ -6285,7 +6325,7 @@ static void record_trace(int argc, char **argv,
if (!latency)
start_threads(type, ctx);
} else {
- update_task_filter();
+ update_task_filter(-1);
tracecmd_enable_tracing();
exit(0);
}
@@ -6293,11 +6333,11 @@ static void record_trace(int argc, char **argv,
if (ctx->run_command) {
run_cmd(type, ctx->user, (argc - optind) - 1, &argv[optind + 1]);
} else if (ctx->instance && is_agent(ctx->instance)) {
- update_task_filter();
+ update_task_filter(-1);
tracecmd_enable_tracing();
tracecmd_msg_wait_close(ctx->instance->msg_handle);
} else {
- update_task_filter();
+ update_task_filter(-1);
tracecmd_enable_tracing();
/* We don't ptrace ourself */
if (do_ptrace && filter_pids) {
--
2.26.2
|