A cgroup resource limitation can be either a number or "max". It means that the cgroup will not be limited _more_ than it already is. This can mean that it will use the kernel limit for the resource, if it exists, or the limit of a parent cgroup.

This patch reworks "read_session_pids_limit" to go up the cgroup hierarchy if it encounters a "max" value rather than a numerical one, using the kernel limit in the event where it doesn't find any.

Clean up uid related code as it is not used anymore.

Signed-off-by: Teo Couprie Diaz teo.coupriediaz@arm.com Co-developed-by: Beata Michalska beata.michalska@arm.com --- lib/tst_pid.c | 96 +++++++++++++++++++++++++++++---------------------- 1 file changed, 54 insertions(+), 42 deletions(-)

diff --git a/lib/tst_pid.c b/lib/tst_pid.c index 98f733d33..0efd67f05 100644 --- a/lib/tst_pid.c +++ b/lib/tst_pid.c @@ -43,50 +43,69 @@ pid_t tst_get_unused_pid_(void (*cleanup_fn) (void)) return pid; }

-/* - * Get the effective session UID - either one invoking current test via sudo - * or the real UID. - */ -static unsigned int get_session_uid(void) +static int __read_pids_limit(const char *path, void (*cleanup_fn) (void)) { - const char *sudo_uid; + char max_pids_value[100]; + int max_pids;

- sudo_uid = getenv("SUDO_UID"); - if (sudo_uid) { - unsigned int real_uid; - int ret; + if (access(path, R_OK) != 0) { + tst_resm(TINFO, "Cannot read session user limits from '%s'", path); + return -1; + }

- ret = sscanf(sudo_uid, "%u", &real_uid); - if (ret == 1) - return real_uid; + SAFE_FILE_SCANF(cleanup_fn, path, "%s", max_pids_value); + if (strcmp(max_pids_value, "max")) { + max_pids = SAFE_STRTOL(max_pids_value, 0, INT_MAX); + tst_resm(TINFO, "Found limit of processes %d (from %s)", + max_pids, path); + } else { + max_pids = -1; }

- return getuid(); + return max_pids; }

-static int read_session_pids_limit(const char *path_fmt, int uid, - void (*cleanup_fn) (void)) +/* + * Take the path to the cgroup mount and to the current cgroup pid controller + * and try to find the PID limit imposed by cgroup. + * Go up the cgroup hierarchy if needed, otherwise use the kernel PID limit. + */ +static int read_session_pids_limit(const char *cgroup_mount, + const char *cgroup_path, void (*cleanup_fn) (void)) { - int max_pids, ret; - char max_pid_value[100]; - char path[PATH_MAX]; - - ret = snprintf(path, sizeof(path), path_fmt, uid); + int ret, cgroup_depth = 0, max_pids = -1; + char path[PATH_MAX + 1], file_path[PATH_MAX + 1]; + const char *sub_path = cgroup_path; + + /* Find the number of groups we can go up. */ + do { + cgroup_depth += 1; + sub_path++; + sub_path = strchr(sub_path, '/'); + } while (sub_path); + + ret = snprintf(path, sizeof(path), "%s%s", cgroup_mount, cgroup_path); if (ret < 0 || (size_t)ret >= sizeof(path)) return -1;

- if (access(path, R_OK) != 0) { - tst_resm(TINFO, "Cannot read session user limits from '%s'", path); - return -1; + for (int i = 0 ; i < cgroup_depth ; i++) { + /* Create a path to read from. */ + ret = snprintf(file_path, sizeof(file_path), "%s/pids.max", path); + if (ret < 0 || (size_t)ret >= sizeof(file_path)) + return -1; + + max_pids = __read_pids_limit(file_path, cleanup_fn); + if (max_pids >= 0) + return max_pids; + + strncat(path, "/..", PATH_MAX); }

- SAFE_FILE_SCANF(cleanup_fn, path, "%s", max_pid_value); - if (!strcmp(max_pid_value, "max")) { + if (max_pids < 0) { + /* Read kernel imposed limits */ SAFE_FILE_SCANF(cleanup_fn, PID_MAX_PATH, "%d", &max_pids); - tst_resm(TINFO, "Found limit of processes %d (from %s=max)", max_pids, path); - } else { - max_pids = SAFE_STRTOL(max_pid_value, 0, INT_MAX); - tst_resm(TINFO, "Found limit of processes %d (from %s)", max_pids, path); + tst_resm(TINFO, "Using kernel processes limit of %d", + max_pids); }

return max_pids; @@ -97,9 +116,8 @@ static int get_session_pids_limit(void (*cleanup_fn) (void)) char path[PATH_MAX + 1]; char cgroup_pids[PATH_MAX + 1]; char catchall; - int uid, ret = 0; + int ret = 0;

- uid = get_session_uid(); /* Check for generic cgroup v1 pid.max */ ret = FILE_LINES_SCANF(cleanup_fn, "/proc/self/cgroup", "%*d:pids:%s\n", cgroup_pids); @@ -120,11 +138,8 @@ static int get_session_pids_limit(void (*cleanup_fn) (void)) "%*s %*s %*s %*s %s %*[^-] - cgroup %*s %*[rw],pid%c", path, &catchall);

- if (!ret) { - strncat(path, cgroup_pids, PATH_MAX); - strncat(path, "/pids.max", PATH_MAX); - return read_session_pids_limit(path, uid, cleanup_fn); - } + if (!ret) + return read_session_pids_limit(path, cgroup_pids, cleanup_fn);

/* Check for generic cgroup v2 pid.max */ ret = FILE_LINES_SCANF(cleanup_fn, "/proc/self/cgroup", @@ -134,11 +149,8 @@ static int get_session_pids_limit(void (*cleanup_fn) (void)) "%*s %*s %*s %*s %s %*[^-] - cgroup2 %c", path, &catchall);

- if (!ret) { - strncat(path, cgroup_pids, PATH_MAX); - strncat(path, "/pids.max", PATH_MAX); - return read_session_pids_limit(path, uid, cleanup_fn); - } + if (!ret) + return read_session_pids_limit(path, cgroup_pids, cleanup_fn);

return -1; }

Landed on next.

Just for keeping the track here: v5 is taking into account the fact that some fields within /proc/$pid/mountinfo are actually optional thus change in the format string while running sscanf on it.

--- BR B. On Wed, Feb 15, 2023 at 09:54:12AM +0000, Teo Couprie Diaz wrote:

In some distributions, the two files used in lib/tst_pid.c are not available, but cgroups still imposes a task limit far smaller than the kernel pid_max. If the cgroup sysfs is mounted, we can use it to retrieve the current task limit imposed to the process. Implement the retrieval of this limit.

This can be done by first checking /proc/self/cgroup to get the cgroup the process is in, which will be a path under the cgroup sysfs. To get the path to the cgroup sysfs, check /proc/self/mountinfo. Finally, concatenate those two paths with pid.max to get the full path to the file containing the limit.

This patch changes the way read_session_pids_limit is called, not passing a format string to be completed anymore, but is still used the same way. A following patch will update this function.

This fixes failures for msgstress04.

Signed-off-by: Teo Couprie Diaz teo.coupriediaz@arm.com

lib/tst_pid.c | 53 +++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 43 insertions(+), 10 deletions(-)

diff --git a/lib/tst_pid.c b/lib/tst_pid.c index 21cadef2a..98f733d33 100644 --- a/lib/tst_pid.c +++ b/lib/tst_pid.c @@ -31,8 +31,6 @@ #include "tst_safe_macros.h" #define PID_MAX_PATH "/proc/sys/kernel/pid_max" -#define CGROUPS_V1_SLICE_FMT "/sys/fs/cgroup/pids/user.slice/user-%d.slice/pids.max" -#define CGROUPS_V2_SLICE_FMT "/sys/fs/cgroup/user.slice/user-%d.slice/pids.max" /* Leave some available processes for the OS */ #define PIDS_RESERVE 50 @@ -96,18 +94,53 @@ static int read_session_pids_limit(const char *path_fmt, int uid, static int get_session_pids_limit(void (*cleanup_fn) (void)) {

• int max_pids, uid;

• char path[PATH_MAX + 1];
• char cgroup_pids[PATH_MAX + 1];
• char catchall;
• int uid, ret = 0;

uid = get_session_uid();

• max_pids = read_session_pids_limit(CGROUPS_V2_SLICE_FMT, uid, cleanup_fn);
• if (max_pids < 0)

• max_pids = read_session_pids_limit(CGROUPS_V1_SLICE_FMT, uid,
  

• 				   cleanup_fn);
  

• /* Check for generic cgroup v1 pid.max */
• ret = FILE_LINES_SCANF(cleanup_fn, "/proc/self/cgroup",

• 				   "%*d:pids:%s\n", cgroup_pids);
  

• /*

• * This is a bit of a hack of scanf format strings. Indeed, if all
  

• * conversion specifications have been matched the return of scanf will be
  

• * the same whether any outstanding literal characters match or not.
  

• * As we want to match the literal part, we can add a catchall after it
  

• * so that it won't be counted if the literal part doesn't match.
  

• * This makes the macro go to the next line until the catchall, thus
  

• * the literal parts, is matched.
  

• *
  

• * Assume that the root of the mount is '/'. It can be anything,
  

• * but it should be '/' on any normal system.
  

• */
  

• if (!ret)

• ret = FILE_LINES_SCANF(cleanup_fn, "/proc/self/mountinfo",
  

• 					   "%*s %*s %*s %*s %s %*[^-] - cgroup %*s %*[rw],pid%c",
  

• 					   path, &catchall);
  

• if (!ret) {

• strncat(path, cgroup_pids, PATH_MAX);
  

• strncat(path, "/pids.max", PATH_MAX);
  

• return read_session_pids_limit(path, uid, cleanup_fn);
  

• }

• if (max_pids < 0)

• return -1;
  

• /* Check for generic cgroup v2 pid.max */
• ret = FILE_LINES_SCANF(cleanup_fn, "/proc/self/cgroup",

• 				   "%*d::%s\n", cgroup_pids);
  

• if (!ret)

• ret = FILE_LINES_SCANF(cleanup_fn, "/proc/self/mountinfo",
  

• 					   "%*s %*s %*s %*s %s %*[^-] - cgroup2 %c",
  

• 					   path, &catchall);
  

• if (!ret) {

• strncat(path, cgroup_pids, PATH_MAX);
  

• strncat(path, "/pids.max", PATH_MAX);
  

• return read_session_pids_limit(path, uid, cleanup_fn);
  

• }

• return max_pids;

• return -1;

} int tst_get_free_pids_(void (*cleanup_fn) (void)) -- 2.25.1

---

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