This patch is for "Hide userland process threads mode is off" case.

Below is a small example of two threads program, whose main thread
statistics is incorrect in htop. Despite main thread is permanently
sleeping, its CPU load is 100% (must be 0%). CPU load of secondary
thread is correct (100%).

void *thread_func(void *data)
{
    while(1) {
    }
    return NULL;
}
int main()
{
    pthread_t thread;
    pthread_create(&thread, NULL, thread_func, NULL);
    pthread_join(thread, NULL);
}

The reason is in there is a difference in behavior of some files
in /proc/pid and /proc/pid/task/pid directories. For example,
/proc/pid/stat shows agregated user and sys times for all threads
of a process. For the details please see do_task_stat() implementation
and this function behavior difference in dependence of last argument:

https://elixir.bootlin.com/linux/v6.2.8/source/fs/proc/array.c#L652

So, the problem occurs because of user and sys times of main thread are
polluted by secondary thread statistics. This patch fixes the problem
by reading correct stat from /proc/pid/task/pid/stat for main thread.

Looking at other files from /proc/pid directory I found /proc/pid/io
file with the same problem:

https://elixir.bootlin.com/linux/v6.2.8/source/fs/proc/base.c#L3029

This problem is also fixed in this patch by reading correct data
from /proc/pid/task/pid/io file for main thread.

/proc/pid directory files are declared in tgid_base_stuff, while
/proc/pid/task/tid directory files are declared in tid_base_stuff
in kernel's fs/proc/base.c file:

https://elixir.bootlin.com/linux/v6.2.8/source/fs/proc/base.c#L3238

I checked the difference between rest of declarations and it looks like
there is no more problems of such type affecting htop.

1 files changed, 18 insertions, 7 deletions

diff --git a/linux/LinuxProcessList.c b/linux/LinuxProcessList.c
index f8d56b70..b94c24a1 100644
--- a/linux/LinuxProcessList.c
+++ b/linux/LinuxProcessList.c
@@ -14,6 +14,7 @@ in the source distribution for its full text.
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <inttypes.h>
 #include <limits.h>
 #include <math.h>
 #include <stdbool.h>
@@ -382,11 +383,15 @@ static inline ProcessState LinuxProcessList_getProcessState(char state) {
    }
 }
 
-static bool LinuxProcessList_readStatFile(Process* process, openat_arg_t procFd, char* command, size_t commLen) {
-   LinuxProcess* lp = (LinuxProcess*) process;
+static bool LinuxProcessList_readStatFile(LinuxProcess* lp, openat_arg_t procFd, bool scanMainThread, char* command, size_t commLen) {
+   Process* process = &lp->super;
 
    char buf[MAX_READ + 1];
-   ssize_t r = xReadfileat(procFd, "stat", buf, sizeof(buf));
+   char path[22] = "stat";
+   if (scanMainThread) {
+      xSnprintf(path, sizeof(path), "task/%"PRIi32"/stat", (int32_t)process->pid);
+   }
+   ssize_t r = xReadfileat(procFd, path, buf, sizeof(buf));
    if (r < 0)
       return false;
 
@@ -607,9 +612,14 @@ static bool LinuxProcessList_updateUser(ProcessList* processList, Process* proce
    return true;
 }
 
-static void LinuxProcessList_readIoFile(LinuxProcess* process, openat_arg_t procFd, unsigned long long realtimeMs) {
+static void LinuxProcessList_readIoFile(LinuxProcess* process, openat_arg_t procFd, bool scanMainThread, unsigned long long realtimeMs) {
+   Process *proc = &process->super;
+   char path[20] = "io";
    char buffer[1024];
-   ssize_t r = xReadfileat(procFd, "io", buffer, sizeof(buffer));
+   if (scanMainThread) {
+      xSnprintf(path, sizeof(path), "task/%"PRIi32"/io", (int32_t)proc->pid);
+   }
+   ssize_t r = xReadfileat(procFd, path, buffer, sizeof(buffer));
    if (r < 0) {
       process->io_rate_read_bps = NAN;
       process->io_rate_write_bps = NAN;
@@ -1531,8 +1541,9 @@ static bool LinuxProcessList_recurseProcTree(LinuxProcessList* this, openat_arg_
          continue;
       }
 
+      bool scanMainThread = !hideUserlandThreads && !Process_isKernelThread(proc) && !parent;
       if (ss->flags & PROCESS_FLAG_IO)
-         LinuxProcessList_readIoFile(lp, procFd, pl->realtimeMs);
+         LinuxProcessList_readIoFile(lp, procFd, scanMainThread, pl->realtimeMs);
 
       if (!LinuxProcessList_readStatmFile(lp, procFd))
          goto errorReadingProcess;
@@ -1580,7 +1591,7 @@ static bool LinuxProcessList_recurseProcTree(LinuxProcessList* this, openat_arg_
       char statCommand[MAX_NAME + 1];
       unsigned long long int lasttimes = (lp->utime + lp->stime);
       unsigned long int tty_nr = proc->tty_nr;
-      if (!LinuxProcessList_readStatFile(proc, procFd, statCommand, sizeof(statCommand)))
+      if (!LinuxProcessList_readStatFile(lp, procFd, scanMainThread, statCommand, sizeof(statCommand)))
          goto errorReadingProcess;
 
       if (lp->flags & PF_KTHREAD) {