[committed][gdb/symtab] Fix data race in ~charset_vector
Tom de Vries
tdevries@suse.de
Thu Jul 14 06:19:25 GMT 2022
Hi,
When doing:
...
$ gdb ./outputs/gdb.ada/char_enum_unicode/foo -batch -ex "break foo.adb:26"
...
with a gdb build with -fsanitize=thread I run into a data race:
...
WARNING: ThreadSanitizer: data race (pid=30917)
Write of size 8 at 0x7b0400004070 by main thread:
#0 free <null> (libtsan.so.2+0x4c5e2)
#1 xfree<char> gdbsupport/gdb-xfree.h:37 (gdb+0x650f17)
#2 charset_vector::clear() gdb/charset.c:703 (gdb+0x651354)
#3 charset_vector::~charset_vector() gdb/charset.c:697 (gdb+0x6512d3)
#4 <null> <null> (libtsan.so.2+0x32643)
#5 captured_main_1 gdb/main.c:1310 (gdb+0xa3975a)
...
The problem is that we're freeing the charset_vector elements in the destructor,
which may still be used by a worker thread.
Fix this by not freeing the charset_vector elements in the destructor.
Tested on x86_64-linux.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29311
Committed to trunk.
Thanks,
- Tom
[gdb/symtab] Fix data race in ~charset_vector
---
gdb/charset.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/gdb/charset.c b/gdb/charset.c
index 74f742e0aa7..a6261fc505c 100644
--- a/gdb/charset.c
+++ b/gdb/charset.c
@@ -694,7 +694,13 @@ struct charset_vector
{
~charset_vector ()
{
- clear ();
+ /* Note that we do not call charset_vector::clear, which would also xfree
+ the elements. This destructor is only called after exit, at which point
+ those will be freed anyway on process exit, so not freeing them now is
+ not classified as a memory leak. OTOH, freeing them now might be
+ classified as a data race, because some worker thread might still be
+ accessing them. */
+ charsets.clear ();
}
void clear ()
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