Unix Programming - memory leak in threaded getpwuid

Author

memory leak in threaded getpwuid_r() usage

knt

2006-01-15, 5:52 pm

Hi,

Trying to use getpwuid_r() in a threaded application. (Code is attached
at the end of the message.) But in the "ps -p <PID> -o rss,size" output
of the program, RSS increases by time while SIZE remains stable.

Here's the (ps -p <PID> -o rss,size) output of the program:

[BEGIN:output]
$ ./a.out
user_id = 1000, proc_id = 28583
1 700 46336
2 704 46336
....
47 716 46332
48 716 46332
49 716 46336
50 716 46336
[END:output]

And valgrind --leak-check=full output:

[BEGIN:valgrind]
156 (36 direct, 120 indirect) bytes in 1 blocks are definitely lost in
loss record 4 of 9
at 0x1B90459D: malloc (vg_replace_malloc.c:130)
by 0x1BA0BEE6: (within /lib/tls/libc-2.3.2.so)
by 0x1BA0B788: __nss_database_lookup (in /lib/tls/libc-2.3.2.so)
by 0x1DB70AFB: ???
by 0x1B9CCD4B: getpwuid_r (in /lib/tls/libc-2.3.2.so)
by 0x804879A: sub_func (getpwuid.c:43)
by 0x1B918B62: start_thread (in /lib/tls/libpthread-0.60.so)
by 0x1B9FC189: clone (in /lib/tls/libc-2.3.2.so)

340 bytes in 5 blocks are possibly lost in loss record 8 of 9
at 0x1B904F75: calloc (vg_replace_malloc.c:175)
by 0x1B8F2678: (within /lib/ld-2.3.2.so)
by 0x1B8F294B: _dl_allocate_tls (in /lib/ld-2.3.2.so)
by 0x1B91924A: allocate_stack (in /lib/tls/libpthread-0.60.so)
by 0x1B918C54: pthread_create@@GLIBC_2.1 (in
/lib/tls/libpthread-0.60.so)
by 0x80488AB: main (getpwuid.c:68)
[END:valgrind]

I'd be so appreciated if somebody can help me to figure out the problem
in the code. (Suggesting mailing lists that I can ask this problem is
welcome too.)

Regards.

[BEGIN:getpwuid.c]
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>

#include "pthread.h"

uid_t user_id;
pid_t proc_id;
char cmd[128];
int iter;

void
print_mem_usage(void)
{
FILE *fp = popen(cmd, "r");
static char buf[64];

if (!fp)
{
fprintf(stderr, "popen() failed!\n");
return;
}

(void) fgets(buf, sizeof(buf), fp);
fgets(buf, sizeof(buf), fp);
printf("%3d %s", iter++, buf);

fclose(fp);

}

void *
sub_func(void *tmp)
{
int ret;
size_t sz = 128;
char buf[sz];

struct passwd old_pw;
struct passwd *new_pw;

ret = getpwuid_r(user_id, &old_pw, buf, sz, &new_pw);
if (ret)
fprintf(stderr, "getpwuid_r() failed! ret = %d\n", ret);

pthread_exit(NULL);

}

int
main(void)
{
int loop_count = 50;
int thread_count = 100;
pthread_t threads[thread_count];
int i, ret;

user_id = getuid();
proc_id = getpid();
sprintf(cmd, "ps -p %d -o rss,size", proc_id);
iter = 1;
printf("user_id = %d, proc_id = %d\n", user_id, proc_id);

while (loop_count--)
{
for (i = 0; i < thread_count; i++)
{
ret = pthread_create(&threads[i], NULL, sub_func, NULL);
if (ret)
fprintf(stderr, "pthread_create() failed! i = %d, ret =
%d\n", i, ret);
}

for (i = 0; i < thread_count; i++)
{
ret = pthread_join(threads[i], NULL);
if (ret)
fprintf(stderr, "pthread_join() failed! i = %d, ret =
%d\n", i, ret);
}

print_mem_usage();
}

return 0;
}
[END:getpwuid.c]

Nils O. Selåsdal

2006-01-15, 5:52 pm

knt wrote:
> Hi,
>
> Trying to use getpwuid_r() in a threaded application. (Code is attached
> at the end of the message.) But in the "ps -p <PID> -o rss,size" output
> of the program, RSS increases by time while SIZE remains stable.
>
> Here's the (ps -p <PID> -o rss,size) output of the program:
>
> [BEGIN:output]
> $
[snip}
Valgrind detects no memory leaks on my system. Perhaps you're using a
NSS module that's abit buggy ?

knt

2006-01-15, 5:52 pm

I'm using latest libnss-db 2.2-6.3 package in the debian stable (sarge)
repository. What's the version of the related softwares (like NSS
module) in your system? Also, when you increase the thread_count, does
ps command output change or remain stable? (ps output remains stable on
your system, ain't?)

Regards.