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From: Tom de Vries <vries@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] [gdb/symtab] Fix data race in ~charset_vector Date: Thu, 14 Jul 2022 06:19:04 +0000 (GMT) [thread overview] Message-ID: <20220714061904.369DC3858D37@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=4f92e10cda142fd1f213e01a53ca687e38cddf22 commit 4f92e10cda142fd1f213e01a53ca687e38cddf22 Author: Tom de Vries <tdevries@suse.de> Date: Thu Jul 14 08:19:00 2022 +0200 [gdb/symtab] Fix data race in ~charset_vector 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 Diff: --- 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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