Separate kernel.Task.AsCopyContext() into CopyContext() and OwnCopyContext().

kernel.copyContext{t} cannot be used outside of t's task goroutine, for three
reasons:

- t.CopyScratchBuffer() is task-goroutine-local.

- Calling t.MemoryManager() without running on t's task goroutine or locking
  t.mu violates t.MemoryManager()'s preconditions.

- kernel.copyContext passes t as context.Context to MM IO methods, which is
  illegal outside of t's task goroutine (cf. kernel.Task.Value()).

Fix this by splitting AsCopyContext() into CopyContext() (which takes an
explicit context.Context and is usable outside of the task goroutine) and
OwnCopyContext() (which uses t as context.Context, but is only usable by t's
task goroutine).

PiperOrigin-RevId: 339933809

2 files changed, 38 insertions, 9 deletions

diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index c94c1d5bd..88899589d 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -1802,10 +1802,14 @@ cc_binary(
         "@com_google_absl//absl/flags:flag",
         "@com_google_absl//absl/time",
         gtest,
+        "//test/util:file_descriptor",
+        "//test/util:fs_util",
         "//test/util:logging",
+        "//test/util:memory_util",
         "//test/util:multiprocess_util",
         "//test/util:platform_util",
         "//test/util:signal_util",
+        "//test/util:temp_path",
         "//test/util:test_util",
         "//test/util:thread_util",
         "//test/util:time_util",
diff --git a/test/syscalls/linux/ptrace.cc b/test/syscalls/linux/ptrace.cc
index 926690eb8..13c19d4a8 100644
--- a/test/syscalls/linux/ptrace.cc
+++ b/test/syscalls/linux/ptrace.cc
@@ -30,10 +30,13 @@
 #include "absl/flags/flag.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "test/util/fs_util.h"
 #include "test/util/logging.h"
+#include "test/util/memory_util.h"
 #include "test/util/multiprocess_util.h"
 #include "test/util/platform_util.h"
 #include "test/util/signal_util.h"
+#include "test/util/temp_path.h"
 #include "test/util/test_util.h"
 #include "test/util/thread_util.h"
 #include "test/util/time_util.h"
@@ -113,10 +116,21 @@ TEST(PtraceTest, AttachParent_PeekData_PokeData_SignalSuppression) {
   // except disabled.
   SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) > 0);
 
-  constexpr long kBeforePokeDataValue = 10;
-  constexpr long kAfterPokeDataValue = 20;
+  // Test PTRACE_POKE/PEEKDATA on both anonymous and file mappings.
+  const auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  ASSERT_NO_ERRNO(Truncate(file.path(), kPageSize));
+  const FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(file.path(), O_RDWR));
+  const auto file_mapping = ASSERT_NO_ERRNO_AND_VALUE(Mmap(
+      nullptr, kPageSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd.get(), 0));
 
-  volatile long word = kBeforePokeDataValue;
+  constexpr long kBeforePokeDataAnonValue = 10;
+  constexpr long kAfterPokeDataAnonValue = 20;
+  constexpr long kBeforePokeDataFileValue = 0;  // implicit, due to truncate()
+  constexpr long kAfterPokeDataFileValue = 30;
+
+  volatile long anon_word = kBeforePokeDataAnonValue;
+  auto* file_word_ptr = static_cast<volatile long*>(file_mapping.ptr());
 
   pid_t const child_pid = fork();
   if (child_pid == 0) {
@@ -134,12 +148,22 @@ TEST(PtraceTest, AttachParent_PeekData_PokeData_SignalSuppression) {
     MaybeSave();
     TEST_CHECK(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
 
-    // Replace the value of word in the parent process with kAfterPokeDataValue.
-    long const parent_word = ptrace(PTRACE_PEEKDATA, parent_pid, &word, 0);
+    // Replace the value of anon_word in the parent process with
+    // kAfterPokeDataAnonValue.
+    long parent_word = ptrace(PTRACE_PEEKDATA, parent_pid, &anon_word, 0);
+    MaybeSave();
+    TEST_CHECK(parent_word == kBeforePokeDataAnonValue);
+    TEST_PCHECK(ptrace(PTRACE_POKEDATA, parent_pid, &anon_word,
+                       kAfterPokeDataAnonValue) == 0);
+    MaybeSave();
+
+    // Replace the value pointed to by file_word_ptr in the mapped file with
+    // kAfterPokeDataFileValue, via the parent process' mapping.
+    parent_word = ptrace(PTRACE_PEEKDATA, parent_pid, file_word_ptr, 0);
     MaybeSave();
-    TEST_CHECK(parent_word == kBeforePokeDataValue);
-    TEST_PCHECK(
-        ptrace(PTRACE_POKEDATA, parent_pid, &word, kAfterPokeDataValue) == 0);
+    TEST_CHECK(parent_word == kBeforePokeDataFileValue);
+    TEST_PCHECK(ptrace(PTRACE_POKEDATA, parent_pid, file_word_ptr,
+                       kAfterPokeDataFileValue) == 0);
     MaybeSave();
 
     // Detach from the parent and suppress the SIGSTOP. If the SIGSTOP is not
@@ -160,7 +184,8 @@ TEST(PtraceTest, AttachParent_PeekData_PokeData_SignalSuppression) {
       << " status " << status;
 
   // Check that the child's PTRACE_POKEDATA was effective.
-  EXPECT_EQ(kAfterPokeDataValue, word);
+  EXPECT_EQ(kAfterPokeDataAnonValue, anon_word);
+  EXPECT_EQ(kAfterPokeDataFileValue, *file_word_ptr);
 }
 
 TEST(PtraceTest, GetSigMask) {