commit 822662cf2a4b170ade4c5342f035d68815a03276

Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Date:   Mon Sep 6 14:19:51 2021 -0300

    linux: Revert the use of sched_getaffinity on get_nproc (BZ #28310)

    The use of sched_getaffinity on get_nproc and

    sysconf (_SC_NPROCESSORS_ONLN) done in 903bc7dcc2acafc40 (BZ #27645)

    breaks the top command in common hypervisor configurations and also

    other monitoring tools.

    The main issue using sched_getaffinity changed the symbols semantic

    from system-wide scope of online CPUs to per-process one (which can

    be changed with kernel cpusets or book parameters in VM).

    This patch reverts mostly of the 903bc7dcc2acafc40, with the

    exceptions:

      * No more cached values and atomic updates, since they are inherent

        racy.

      * No /proc/cpuinfo fallback, since /proc/stat is already used and

        it would require to revert more arch-specific code.

      * The alloca is replace with a static buffer of 1024 bytes.

    So the implementation first consult the sysfs, and fallbacks to procfs.

    Checked on x86_64-linux-gnu.

    Reviewed-by: Florian Weimer <fweimer@redhat.com>

    (cherry picked from commit 342298278eabc75baabcaced110a11a02c3d3580)

diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c

index 61d20e7bab8640f2..d70ed9586950615c 100644

--- a/sysdeps/unix/sysv/linux/getsysstats.c

+++ b/sysdeps/unix/sysv/linux/getsysstats.c

@@ -18,6 +18,8 @@

    <https://www.gnu.org/licenses/>.  */

 #include <array_length.h>

+#include <assert.h>

+#include <ctype.h>

 #include <dirent.h>

 #include <errno.h>

 #include <ldsodefs.h>

@@ -30,7 +32,7 @@

 #include <sysdep.h>

 int

-__get_nprocs (void)

+__get_nprocs_sched (void)

 {

   enum

     {

@@ -53,14 +55,141 @@ __get_nprocs (void)

      atomics are needed). */

   return 2;

 }

-libc_hidden_def (__get_nprocs)

-weak_alias (__get_nprocs, get_nprocs)

+

+static char *

+next_line (int fd, char *const buffer, char **cp, char **re,

+           char *const buffer_end)

+{

+  char *res = *cp;

+  char *nl = memchr (*cp, '\n', *re - *cp);

+  if (nl == NULL)

+    {

+      if (*cp != buffer)

+        {

+          if (*re == buffer_end)

+            {

+              memmove (buffer, *cp, *re - *cp);

+              *re = buffer + (*re - *cp);

+              *cp = buffer;

+

+              ssize_t n = __read_nocancel (fd, *re, buffer_end - *re);

+              if (n < 0)

+                return NULL;

+

+              *re += n;

+

+              nl = memchr (*cp, '\n', *re - *cp);

+              while (nl == NULL && *re == buffer_end)

+                {

+                  /* Truncate too long lines.  */

+                  *re = buffer + 3 * (buffer_end - buffer) / 4;

+                  n = __read_nocancel (fd, *re, buffer_end - *re);

+                  if (n < 0)

+                    return NULL;

+

+                  nl = memchr (*re, '\n', n);

+                  **re = '\n';

+                  *re += n;

+                }

+            }

+          else

+            nl = memchr (*cp, '\n', *re - *cp);

+

+          res = *cp;

+        }

+

+      if (nl == NULL)

+        nl = *re - 1;

+    }

+

+  *cp = nl + 1;

+  assert (*cp <= *re);

+

+  return res == *re ? NULL : res;

+}

+

 int

-__get_nprocs_sched (void)

+__get_nprocs (void)

 {

-  return __get_nprocs ();

+  enum { buffer_size = 1024 };

+  char buffer[buffer_size];

+  char *buffer_end = buffer + buffer_size;

+  char *cp = buffer_end;

+  char *re = buffer_end;

+

+  const int flags = O_RDONLY | O_CLOEXEC;

+  /* This file contains comma-separated ranges.  */

+  int fd = __open_nocancel ("/sys/devices/system/cpu/online", flags);

+  char *l;

+  int result = 0;

+  if (fd != -1)

+    {

+      l = next_line (fd, buffer, &cp, &re, buffer_end);

+      if (l != NULL)

+	do

+	  {

+	    char *endp;

+	    unsigned long int n = strtoul (l, &endp, 10);

+	    if (l == endp)

+	      {

+		result = 0;

+		break;

+	      }

+

+	    unsigned long int m = n;

+	    if (*endp == '-')

+	      {

+		l = endp + 1;

+		m = strtoul (l, &endp, 10);

+		if (l == endp)

+		  {

+		    result = 0;

+		    break;

+		  }

+	      }

+

+	    result += m - n + 1;

+

+	    l = endp;

+	    if (l < re && *l == ',')

+	      ++l;

+	  }

+	while (l < re && *l != '\n');

+

+      __close_nocancel_nostatus (fd);

+

+      if (result > 0)

+	return result;

+    }

+

+  cp = buffer_end;

+  re = buffer_end;

+

+  /* Default to an SMP system in case we cannot obtain an accurate

+     number.  */

+  result = 2;

+

+  fd = __open_nocancel ("/proc/stat", flags);

+  if (fd != -1)

+    {

+      result = 0;

+

+      while ((l = next_line (fd, buffer, &cp, &re, buffer_end)) != NULL)

+	/* The current format of /proc/stat has all the cpu* entries

+	   at the front.  We assume here that stays this way.  */

+	if (strncmp (l, "cpu", 3) != 0)

+	  break;

+	else if (isdigit (l[3]))

+	  ++result;

+

+      __close_nocancel_nostatus (fd);

+    }

+

+  return result;

 }

+libc_hidden_def (__get_nprocs)

+weak_alias (__get_nprocs, get_nprocs)

 /* On some architectures it is possible to distinguish between configured