[Lldb-commits] [PATCH] D83359: [SymbolFileDWARF] Lock the module when parsing call site info

[Vedant Kumar via Phabricator via lldb-commits]

vsk updated this revision to Diff 276280.
vsk added a comment.

Move locking up into lldb::Function, and leave a comment in SymbolFileDWARF 
explaining why.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D83359/new/

https://reviews.llvm.org/D83359

Files:
  lldb/include/lldb/Symbol/Function.h
  lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
  lldb/source/Symbol/Function.cpp


Index: lldb/source/Symbol/Function.cpp
===
--- lldb/source/Symbol/Function.cpp
+++ lldb/source/Symbol/Function.cpp
@@ -290,6 +290,8 @@
 }
 
 llvm::ArrayRef> Function::GetCallEdges() {
+  std::lock_guard guard(m_call_edges_lock);
+
   if (m_call_edges_resolved)
 return m_call_edges;
 
Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -3844,6 +3844,11 @@
 
 std::vector>
 SymbolFileDWARF::ParseCallEdgesInFunction(UserID func_id) {
+  // ParseCallEdgesInFunction must be called at the behest of an exclusively
+  // locked lldb::Function instance. Storage for parsed call edges is owned by
+  // the lldb::Function instance: locking at the SymbolFile level would be too
+  // late, because the act of storing results from ParseCallEdgesInFunction
+  // would be racy.
   DWARFDIE func_die = GetDIE(func_id.GetID());
   if (func_die.IsValid())
 return CollectCallEdges(GetObjectFile()->GetModule(), func_die);
Index: lldb/include/lldb/Symbol/Function.h
===
--- lldb/include/lldb/Symbol/Function.h
+++ lldb/include/lldb/Symbol/Function.h
@@ -17,6 +17,8 @@
 #include "lldb/Utility/UserID.h"
 #include "llvm/ADT/ArrayRef.h"
 
+#include 
+
 namespace lldb_private {
 
 class ExecutionContext;
@@ -655,6 +657,9 @@
   uint32_t
   m_prologue_byte_size; ///< Compute the prologue size once and cache it
 
+  std::mutex
+  m_call_edges_lock; ///< Exclusive lock that controls read/write
+ ///  access to m_call_edges and m_call_edges_resolved.
   bool m_call_edges_resolved = false; ///< Whether call site info has been
   ///  parsed.
   std::vector> m_call_edges; ///< Outgoing call 
edges.


Index: lldb/source/Symbol/Function.cpp
===
--- lldb/source/Symbol/Function.cpp
+++ lldb/source/Symbol/Function.cpp
@@ -290,6 +290,8 @@
 }
 
 llvm::ArrayRef> Function::GetCallEdges() {
+  std::lock_guard guard(m_call_edges_lock);
+
   if (m_call_edges_resolved)
 return m_call_edges;
 
Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -3844,6 +3844,11 @@
 
 std::vector>
 SymbolFileDWARF::ParseCallEdgesInFunction(UserID func_id) {
+  // ParseCallEdgesInFunction must be called at the behest of an exclusively
+  // locked lldb::Function instance. Storage for parsed call edges is owned by
+  // the lldb::Function instance: locking at the SymbolFile level would be too
+  // late, because the act of storing results from ParseCallEdgesInFunction
+  // would be racy.
   DWARFDIE func_die = GetDIE(func_id.GetID());
   if (func_die.IsValid())
 return CollectCallEdges(GetObjectFile()->GetModule(), func_die);
Index: lldb/include/lldb/Symbol/Function.h
===
--- lldb/include/lldb/Symbol/Function.h
+++ lldb/include/lldb/Symbol/Function.h
@@ -17,6 +17,8 @@
 #include "lldb/Utility/UserID.h"
 #include "llvm/ADT/ArrayRef.h"
 
+#include 
+
 namespace lldb_private {
 
 class ExecutionContext;
@@ -655,6 +657,9 @@
   uint32_t
   m_prologue_byte_size; ///< Compute the prologue size once and cache it
 
+  std::mutex
+  m_call_edges_lock; ///< Exclusive lock that controls read/write
+ ///  access to m_call_edges and m_call_edges_resolved.
   bool m_call_edges_resolved = false; ///< Whether call site info has been
   ///  parsed.
   std::vector> m_call_edges; ///< Outgoing call edges.
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[Lldb-commits] [PATCH] D83359: [SymbolFileDWARF] Lock the module when parsing call site info

[Vedant Kumar via Phabricator via lldb-commits]

vsk planned changes to this revision.
vsk added a comment.

Hm, this doesn't totally fix the race. If the mutex is contested, the Function 
instance may overwrite its m_call_edges vector.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D83359/new/

https://reviews.llvm.org/D83359



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[Lldb-commits] [PATCH] D83359: [SymbolFileDWARF] Lock the module when parsing call site info

[Vedant Kumar via Phabricator via lldb-commits]

vsk created this revision.
vsk added reviewers: jasonmolenda, friss, jingham.
Herald added a subscriber: aprantl.
Herald added a project: LLDB.

DWARF-parsing methods in SymbolFileDWARF which update module state
should take the module lock. Have ParseCallEdgesInFunction do this.

This could explain some as-of-yet unreproducible crashes which occur in
Function::GetTailCallingEdges(), in which the `m_call_edges` vector is
both non-empty and contains a nullptr, which shouldn't be possible. (If
this vector is non-empty, it _must_ contain a non-null unique_ptr.)

This may address rdar://55622443, rdar://65119458.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83359

Files:
  lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp


Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -3844,6 +3844,7 @@
 
 std::vector>
 SymbolFileDWARF::ParseCallEdgesInFunction(UserID func_id) {
+  std::lock_guard guard(GetModuleMutex());
   DWARFDIE func_die = GetDIE(func_id.GetID());
   if (func_die.IsValid())
 return CollectCallEdges(GetObjectFile()->GetModule(), func_die);


Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -3844,6 +3844,7 @@
 
 std::vector>
 SymbolFileDWARF::ParseCallEdgesInFunction(UserID func_id) {
+  std::lock_guard guard(GetModuleMutex());
   DWARFDIE func_die = GetDIE(func_id.GetID());
   if (func_die.IsValid())
 return CollectCallEdges(GetObjectFile()->GetModule(), func_die);
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