From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 3372C385BF81; Thu, 2 Jul 2020 21:47:42 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 3372C385BF81 From: "simark at simark dot ca" To: gdb-prs@sourceware.org Subject: [Bug gdb/26199] New: GDB goes in busy loop when interrupting non-stop program Date: Thu, 02 Jul 2020 21:47:42 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gdb X-Bugzilla-Component: gdb X-Bugzilla-Version: HEAD X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: simark at simark dot ca X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: unassigned at sourceware dot org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://sourceware.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gdb-prs@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-prs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 02 Jul 2020 21:47:42 -0000 https://sourceware.org/bugzilla/show_bug.cgi?id=3D26199 Bug ID: 26199 Summary: GDB goes in busy loop when interrupting non-stop program Product: gdb Version: HEAD Status: NEW Severity: normal Priority: P2 Component: gdb Assignee: unassigned at sourceware dot org Reporter: simark at simark dot ca Target Milestone: --- When interrupting a program in non-stop, the program gets interrupted correctly, but GDB busy loops (the event loop is always woken up). This is what I did: 1. Start GDB: ./gdb -nx --data-directory=3Ddata-directory -ex "set non-stop= 1" --args /bin/sleep 60 2. Run the program with "run" 3. Interrupt with ^C. 4. Look into htop, see GDB taking 100% CPU Debugging `handle_file_event`, we see that the event source that wakes up t= he event loop is the linux-nat one: (top-gdb) p file_ptr.proc=20 $5 =3D (handler_func *) 0xb9cccd ^^^^^^^^^^^^^^^^^^^- the linux-nat callback Debugging fetch_inferior_event and do_target_wait, we see that we don't actually call `wait` on the linux-nat target, because inferior_matches retu= rns false: auto inferior_matches =3D [&wait_ptid] (inferior *inf) { return (inf->process_target () !=3D NULL && (threads_are_executing (inf->process_target ()) || threads_are_resumed_pending_p (inf)) && ptid_t (inf->pid).matches (wait_ptid)); }; because `threads_are_executing` is false. So what I'm guess happens is: 1. User types ctrl-c, that writes in the linux-nat pipe, waking up the event source 2. linux-nat's wait gets called, the SIGINT event is returned, but before returning, it marks the pipe again, in order for wait to get called again: /* If we requested any event, and something came out, assume there may be more. If we requested a specific lwp or process, also assume there may be more. */ if (target_is_async_p () && ((ourstatus->kind !=3D TARGET_WAITKIND_IGNORE && ourstatus->kind !=3D TARGET_WAITKIND_NO_RESUMED) || ptid !=3D minus_one_ptid)) async_file_mark (); 3. The SIGINT event is handled, the program is stopped, the stop notificati= on is printed 4. The event loop is woken up again because of the `async_file_mark` of ste= p 2. 5. Because `inferior_matches` returns false, we never call linux-nat's wait= , so the pipe stays readable. Rinse and repeat. The first commit that does this is the multi-target one (5b6d1e4fa4fc6 "Multi-target support"). --=20 You are receiving this mail because: You are on the CC list for the bug.=