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 | 34 +++++++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 1e4d38fa..2b5cd42a 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>
@@ -1487,18 +1488,35 @@ 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_t *sem_run;
int status;
int pid;
+ sem_init = sem_open(TRACE_INIT_SEM, O_CREAT, S_IRUSR|S_IWUSR, 0);
+ if (sem_init == SEM_FAILED)
+ die("failed to init trace_cmd init semaphore");
+
+ sem_run = sem_open(TRACE_RUN_SEM, O_CREAT, S_IRUSR|S_IWUSR, 0);
+ if (sem_run == SEM_FAILED) {
+ sem_close(sem_init);
+ sem_unlink(TRACE_INIT_SEM);
+ die("failed to init trace_cmd run semaphore");
+ }
+
if ((pid = fork()) < 0)
die("failed to fork");
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.
@@ -1519,11 +1537,17 @@ 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();
+ sem_post(sem_init);
+ sem_wait(sem_run);
+ sem_close(sem_init);
+ sem_unlink(TRACE_INIT_SEM);
+ sem_close(sem_run);
+ sem_unlink(TRACE_RUN_SEM);
+
+ if (do_ptrace)
ptrace_wait(type);
- } else
+ else
trace_waitpid(type, pid, &status, 0);
}
--
2.25.4
|