[compiler-rt] During profile flushing, setup SIGKILL mask earlier

[serge-sans-paille]

In multi threaded application, it is possible for one thread to terminate the program while another is flushing profile information. We setup a signal mask to delay SIGKILL so that we can safely flush the profile.

This patch setups the mask earlier: it reduces the window during which a SIGKILL can end the computation prematurely.

This fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1850940, where a profiled firefox was encountering several:

LLVM Profile Error: Failed to write file "default_*.profraw": Broken pipe

[llvmbot]

@llvm/pr-subscribers-pgo

Changes

In multi threaded application, it is possible for one thread to terminate the program while another is flushing profile information. We setup a signal mask to delay SIGKILL so that we can safely flush the profile.

This patch setups the mask earlier: it reduces the window during which a SIGKILL can end the computation prematurely.

This fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1850940, where a profiled firefox was encountering several:

LLVM Profile Error: Failed to write file "default_*.profraw": Broken pipe

---

Full diff: https://github.com/llvm/llvm-project/pull/68622.diff

1 Files Affected:

• (modified) compiler-rt/lib/profile/InstrProfilingFile.c (+16-8)

diff --git a/compiler-rt/lib/profile/InstrProfilingFile.c b/compiler-rt/lib/profile/InstrProfilingFile.c
index 5556eccbf578790..ae7872c63f796c0 100644
--- a/compiler-rt/lib/profile/InstrProfilingFile.c
+++ b/compiler-rt/lib/profile/InstrProfilingFile.c
@@ -1034,10 +1034,14 @@ int __llvm_profile_write_file(void) {
   int rc, Length;
   const char *Filename;
   char *FilenameBuf;
-  int PDeathSig = 0;
+
+  // Temporarily suspend getting SIGKILL when the parent exits.
+  int PDeathSig = lprofSuspendSigKill();
 
   if (lprofProfileDumped() || __llvm_profile_is_continuous_mode_enabled()) {
     PROF_NOTE("Profile data not written to file: %s.\n", "already written");
+    if (PDeathSig == 1)
+      lprofRestoreSigKill();
     return 0;
   }
 
@@ -1048,6 +1052,8 @@ int __llvm_profile_write_file(void) {
   /* Check the filename. */
   if (!Filename) {
     PROF_ERR("Failed to write file : %s\n", "Filename not set");
+    if (PDeathSig == 1)
+      lprofRestoreSigKill();
     return -1;
   }
 
@@ -1057,12 +1063,11 @@ int __llvm_profile_write_file(void) {
              "expected %d, but get %d\n",
              INSTR_PROF_RAW_VERSION,
              (int)GET_VERSION(__llvm_profile_get_version()));
+    if (PDeathSig == 1)
+      lprofRestoreSigKill();
     return -1;
   }
 
-  // Temporarily suspend getting SIGKILL when the parent exits.
-  PDeathSig = lprofSuspendSigKill();
-
   /* Write profile data to the file. */
   rc = writeFile(Filename);
   if (rc)
@@ -1095,7 +1100,9 @@ int __llvm_orderfile_write_file(void) {
   int rc, Length, LengthBeforeAppend, SuffixLength;
   const char *Filename;
   char *FilenameBuf;
-  int PDeathSig = 0;
+
+  // Temporarily suspend getting SIGKILL when the parent exits.
+  int PDeathSig = lprofSuspendSigKill();
 
   SuffixLength = strlen(OrderFileSuffix);
   Length = getCurFilenameLength() + SuffixLength;
@@ -1105,6 +1112,8 @@ int __llvm_orderfile_write_file(void) {
   /* Check the filename. */
   if (!Filename) {
     PROF_ERR("Failed to write file : %s\n", "Filename not set");
+    if (PDeathSig == 1)
+      lprofRestoreSigKill();
     return -1;
   }
 
@@ -1119,12 +1128,11 @@ int __llvm_orderfile_write_file(void) {
              "expected %d, but get %d\n",
              INSTR_PROF_RAW_VERSION,
              (int)GET_VERSION(__llvm_profile_get_version()));
+    if (PDeathSig == 1)
+      lprofRestoreSigKill();
     return -1;
   }
 
-  // Temporarily suspend getting SIGKILL when the parent exits.
-  PDeathSig = lprofSuspendSigKill();
-
   /* Write order data to the file. */
   rc = writeOrderFile(Filename);
   if (rc)

[serge-sans-paille]

Thanks @ZequanWu for the review!