[binutils-gdb] [gdb] Block SIGTERM in worker threads

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6418644b0d09af7d1334cc034a7bf8674c061d6e

commit 6418644b0d09af7d1334cc034a7bf8674c061d6e
Author: Tom de Vries <tdevries@suse.de>
Date:   Thu Jun 30 13:31:06 2022 +0200

    [gdb] Block SIGTERM in worker threads
    
    With gdb build with gcc-12 and -fsanitize=thread, and test-case
    gdb.base/gdb-sigterm.exp, I run into:
    ...
    WARNING: ThreadSanitizer: data race (pid=9722)^M
      Write of size 4 at 0x00000325bc68 by thread T1:^M
      #0 handle_sigterm(int) src/gdb/event-top.c:1211 (gdb+0x8ec01f)^M
      ...
      Previous read of size 4 at 0x00000325bc68 by main thread:^M
        [failed to restore the stack]^M
    ^M
      Location is global 'sync_quit_force_run' of size 4 at \
      0x00000325bc68 (gdb+0x325bc68)^M
      ...
    SUMMARY: ThreadSanitizer: data race gdb/event-top.c:1211 in \
      handle_sigterm(int)^M
    ...
    and 3 more data races involving handle_sigterm and locations:
    - active_ext_lang
    - quit_flag
    - heap block of size 40
      (XNEW (async_signal_handler) in create_async_signal_handler)
    
    This was reported in PR29297.
    
    The testcase executes a "kill -TERM $gdb_pid", which generates a
    process-directed signal.
    
    A process-directed signal can be delivered to any thread, and what we see
    here is the fallout of the signal being delivered to a worker thread rather
    than the main thread.
    
    Fix this by blocking SIGTERM in the worker threads.
    
    [ I have not been able to reproduce this after it occurred for the first time,
    so unfortunately I cannot confirm that the patch fixes the problem. ]
    
    Tested on x86_64-linux, with and without -fsanitize=thread.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29297

Diff:
---
 gdbsupport/block-signals.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gdbsupport/block-signals.h b/gdbsupport/block-signals.h
index cf97208c750..4703690a4ec 100644
--- a/gdbsupport/block-signals.h
+++ b/gdbsupport/block-signals.h
@@ -42,6 +42,7 @@ public:
     sigaddset (&mask, SIGCHLD);
     sigaddset (&mask, SIGALRM);
     sigaddset (&mask, SIGWINCH);
+    sigaddset (&mask, SIGTERM);
     gdb_sigmask (SIG_BLOCK, &mask, &m_old_mask);
 #endif
   }