[lldb] Fix lock inversion between statusline mutex and output mutex

[JDevlieghere]

Fix a deadlock between the statusline mutex (in Debugger) and the output
file mutex (in LockedStreamFile). The deadlock occurs when the main
thread is calling the statusline callback while holding the output mutex
in Editline, while the default event thread is trying to update the
statusline.

Extend the uncritical section so we can redraw the statusline there.
The loop in Editline::GetCharacter should be unnecessary. It would only
loop if we had a successful read with length zero, which shouldn't be
possible or when we can't convert a partial UTF-8 character, in which
case we bail out.

rdar://149251156

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Jonas Devlieghere (JDevlieghere)

Changes

Fix a deadlock between the statusline mutex (in Debugger) and the output file mutex (in LockedStreamFile). The deadlock occurs when the main thread is calling the statusline callback while holding the output mutex in Editline, while the default event thread is trying to update the stausline.

rdar://149251156

---

Full diff: https://github.com/llvm/llvm-project/pull/135956.diff

1 Files Affected:

• (modified) lldb/source/Host/common/Editline.cpp (+4-1)

diff --git a/lldb/source/Host/common/Editline.cpp b/lldb/source/Host/common/Editline.cpp
index 29abaf7c65f28..6900da9909eb8 100644
--- a/lldb/source/Host/common/Editline.cpp
+++ b/lldb/source/Host/common/Editline.cpp
@@ -567,8 +567,11 @@ int Editline::GetCharacter(EditLineGetCharType *c) {
     m_needs_prompt_repaint = false;
   }
 
-  if (m_redraw_callback)
+  if (m_redraw_callback) {
+    m_locked_output.reset();
     m_redraw_callback();
+    m_locked_output.emplace(m_output_stream_sp->Lock());
+  }
 
   if (m_multiline_enabled) {
     // Detect when the number of rows used for this input line changes due to

[jasonmolenda]

Looks good, thanks!