Port to 3.1 - Fix getting affinity set on MUSL on Jetson TX2 (#27957)

Ports https://github.com/dotnet/runtime/pull/206 to release/3.1.

The code in PAL_GetCurrentThreadAffinitySet relied on the fact that the
number of processors reported as configured in the system is always
larger than the maximum CPU index. However, it turns out that it is not
true on some devices / distros. The Jetson TX2 reports CPUs 0, 3, 4 and
5 in the affinity mask and the 1 and 2 are never reported. GLIBC reports
6 as the number of configured CPUs, however MUSL reports just 4. The
PAL_GetCurrentThreadAffinitySet was using the number of CPUs reported as
configured as the upper bound for scanning affinity set, so on Jetson
TX2, the affinity mask returned had just two bits set while there were
4 CPUs. That triggered an assert in the GCToOSInterface::Initialize.

This change fixes that by reading the maximum CPU index from the
/proc/cpuinfo. It falls back to using the number of processors
configured when the /proc/cpuinfo is not available (on macOS, FreeBSD, ...)

Fixes https://github.com/dotnet/runtime/issues/170

1 files changed, 1 insertions, 2 deletions

diff --git a/src/pal/src/thread/thread.cpp b/src/pal/src/thread/thread.cpp
index 42209a6028..1bc89944dd 100644
--- a/src/pal/src/thread/thread.cpp
+++ b/src/pal/src/thread/thread.cpp
@@ -3079,10 +3079,9 @@ PAL_GetCurrentThreadAffinitySet(SIZE_T size, UINT_PTR* data)
     if (st == 0)
     {
         const SIZE_T BitsPerBitsetEntry = 8 * sizeof(UINT_PTR);
-        int nrcpus = PAL_GetTotalCpuCount();
 
         // Get info for as much processors as it is possible to fit into the resulting set
-        SIZE_T remainingCount = std::min(size * BitsPerBitsetEntry, (SIZE_T)nrcpus);
+        SIZE_T remainingCount = std::min(size * BitsPerBitsetEntry, (SIZE_T)CPU_SETSIZE);
         SIZE_T i = 0;
         while (remainingCount != 0)
         {