[Openmp-commits] [PATCH] D142175: [OpenMP] Create a temp file in /tmp if /dev/shm is not accessible

[Shilei Tian via Phabricator via Openmp-commits]

tianshilei1992 created this revision.
tianshilei1992 added reviewers: jdoerfert, AndreyChurbanov, tlwilmar, jlpeyton.
Herald added subscribers: guansong, yaxunl.
Herald added a project: All.
tianshilei1992 requested review of this revision.
Herald added subscribers: openmp-commits, sstefan1.
Herald added a project: OpenMP.

When `libomp` is initialized, it creates a temp file in `/dev/shm` to store
registration flag. Some systems, like Android, doesn't have `/dev/shm`, this
feature is disabled by the macro `KMP_USE_SHM`, though most Linux distribution
has that. However, some customized distribution, such as the one reported in
https://github.com/llvm/llvm-project/issues/53955, doesn't support it either.
It causes a core dump. In this patch, if it is the case, we will try to create a
temporary file in `/tmp`, and if it still doesn't make it, then we error out.
Note that we don't consider in this patch if the temporary directory has been
set to `TMPDIR` in this patch. If `/tmp` is not accessible, we error out.

Fix #53955.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D142175

Files:
  openmp/runtime/src/kmp_runtime.cpp


Index: openmp/runtime/src/kmp_runtime.cpp
===================================================================
--- openmp/runtime/src/kmp_runtime.cpp
+++ openmp/runtime/src/kmp_runtime.cpp
@@ -24,6 +24,7 @@
 #include "kmp_wait_release.h"
 #include "kmp_wrapper_getpid.h"
 #include "kmp_dispatch.h"
+#include <cstdio>
 #if KMP_USE_HIER_SCHED
 #include "kmp_dispatch_hier.h"
 #endif
@@ -6739,6 +6740,11 @@
 #endif
 } // __kmp_reg_status_get
 
+#if defined(KMP_USE_SHM)
+// If /dev/shm is not accessible, we will create a temporary file under /tmp.
+char *temp_reg_status_file_name = nullptr;
+#endif
+
 void __kmp_register_library_startup(void) {
 
   char *name = __kmp_reg_status_name(); // Name of the environment variable.
@@ -6781,10 +6787,17 @@
         shm_preexist = 1;
       }
     } else if (fd1 == -1) { // SHM didn't open; it was due to error other than
-      // already exists.
-      // error out here.
-      __kmp_fatal(KMP_MSG(FunctionError, "Can't open SHM2"), KMP_ERR(errno),
-                  __kmp_msg_null);
+      // Already exists. Try to create a temp file under /tmp.
+      // TODO: /tmp might not always be the temporary directory. For now we will
+      // not consider TMPDIR. If /tmp is not accessible, we simply error out.
+      char *temp_file_name = __kmp_str_format("/tmp/%sXXXXXX", name);
+      fd1 = mkstemp(temp_file_name);
+      if (fd1 == -1) {
+        // error out here.
+        __kmp_fatal(KMP_MSG(FunctionError, "Can't open TEMP"), KMP_ERR(errno),
+                    __kmp_msg_null);
+      }
+      temp_reg_status_file_name = temp_file_name;
     }
     if (shm_preexist == 0) {
       // we created SHM now set size
@@ -6896,11 +6909,18 @@
   char *value = NULL;
 
 #if defined(KMP_USE_SHM)
+  bool use_shm = true;
   char *shm_name = __kmp_str_format("/%s", name);
   int fd1 = shm_open(shm_name, O_RDONLY, 0666);
   if (fd1 == -1) {
-    // file did not open. return.
-    return;
+    // file did not open. Try the temporary file.
+    use_shm = false;
+    FILE *tf = fopen(temp_reg_status_file_name, O_RDONLY);
+    if (!tf) {
+      // give it up now.
+      return;
+    }
+    fd1 = fileno(tf);
   }
   char *data1 = (char *)mmap(0, SHM_SIZE, PROT_READ, MAP_SHARED, fd1, 0);
   if (data1 != MAP_FAILED) {
@@ -6917,7 +6937,12 @@
   if (value != NULL && strcmp(value, __kmp_registration_str) == 0) {
 //  Ok, this is our variable. Delete it.
 #if defined(KMP_USE_SHM)
-    shm_unlink(shm_name); // this removes file in /dev/shm
+    if (use_shm) {
+      shm_unlink(shm_name); // this removes file in /dev/shm
+    } else {
+      KMP_DEBUG_ASSERT(temp_reg_status_file_name);
+      unlink(temp_reg_status_file_name); // this removes the temp file
+    }
 #else
     __kmp_env_unset(name);
 #endif
@@ -6925,6 +6950,10 @@
 
 #if defined(KMP_USE_SHM)
   KMP_INTERNAL_FREE(shm_name);
+  if (!use_shm) {
+    KMP_DEBUG_ASSERT(temp_reg_status_file_name);
+    KMP_INTERNAL_FREE(temp_reg_status_file_name);
+  }
 #endif
 
   KMP_INTERNAL_FREE(__kmp_registration_str);


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