From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57902) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V7QrW-0006CW-2R for qemu-devel@nongnu.org; Thu, 08 Aug 2013 10:06:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V7QrR-0002he-2G for qemu-devel@nongnu.org; Thu, 08 Aug 2013 10:06:46 -0400 Sender: fluxion Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable From: Michael Roth In-Reply-To: <20130808140308.20939.20529@loki> References: <1375960178-10882-1-git-send-email-james.hogan@imgtec.com> <20130808140308.20939.20529@loki> Message-ID: <20130808140637.20939.85485@loki> Date: Thu, 08 Aug 2013 09:06:37 -0500 Subject: Re: [Qemu-devel] [PATCH] qemu-char: fix infinite recursion connecting to monitor pty List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: James Hogan , qemu-devel Cc: "James Hogan , Anthony Liguori" , qemu-stable@nongnu.org Quoting Michael Roth (2013-08-08 09:03:08) > Quoting James Hogan (2013-08-08 06:09:38) > > Since commit bd5c51e (qemu-char: don't issue CHR_EVENT_OPEN in a BH), an > > infinite recursion occurs when putting the monitor on a pty (-monitor > > pty) and connecting a terminal to the slave port. > > = > > This is because of the qemu_chr_be_event(s, CHR_EVENT_OPENED) added to > > qemu_chr_be_generic_open(). This event is captured by monitor_event() > > which prints a welcome message to the character device. The flush of > > that welcome message retriggers another open event in pty_chr_state() > > because it checks s->connected, but only sets it to 1 after calling > > qemu_chr_be_generic_open(). > > = > > I've fixed this by setting s->connected =3D 1 before the call to > > qemu_chr_be_generic_open() instead of after, so that the recursive > > pty_chr_state() doesn't call it again. > > = > > An example snippet of repeating backtrace: > > ... > > #107486 0x007aec58 in monitor_flush (mon=3D0xf418b0) at qemu/monitor.c= :288 > > #107487 0x007aee7c in monitor_puts (mon=3D0xf418b0, str=3D0x1176d07 ""= ) at qemu/monitor.c:322 > > #107488 0x007aef20 in monitor_vprintf (mon=3D0xf418b0, fmt=3D0x8d4820 = "QEMU %s monitor - type 'help' for more information\n", > > ap=3D0x7f432be0) at qemu/monitor.c:339 > > #107489 0x007aefac in monitor_printf (mon=3D0xf418b0, fmt=3D0x8d4820 "= QEMU %s monitor - type 'help' for more information\n") > > at qemu/monitor.c:347 > > #107490 0x007ba4bc in monitor_event (opaque=3D0xf418b0, event=3D2) at = qemu/monitor.c:4699 > > #107491 0x00684c28 in qemu_chr_be_event (s=3D0xf37788, event=3D2) at q= emu/qemu-char.c:108 > > #107492 0x00684c70 in qemu_chr_be_generic_open (s=3D0xf37788) at qemu/= qemu-char.c:113 > > #107493 0x006880a4 in pty_chr_state (chr=3D0xf37788, connected=3D1) at= qemu/qemu-char.c:1145 > > #107494 0x00687fa4 in pty_chr_update_read_handler (chr=3D0xf37788) at = qemu/qemu-char.c:1121 > > #107495 0x00687c9c in pty_chr_write (chr=3D0xf37788, buf=3D0x70b3c008 =
, len=3D538720) > > at qemu/qemu-char.c:1063 > > #107496 0x00684cc4 in qemu_chr_fe_write (s=3D0xf37788, buf=3D0x70b3c00= 8
, len=3D538720) > > at qemu/qemu-char.c:118 > > ... > > = > > Signed-off-by: James Hogan > > Cc: Michael Roth > > Cc: Anthony Liguori > = > Thanks for the catch! > = > I reproduced the bug and can confirm the this fixes it. > = > Prior to bd5c51e, the code relied on deferring CHR_EVENT_OPENED via BH to > ensure setting s->connected =3D 1 was visible by the time the event was > processed, so this patch simply makes that ordering explicit. > = > Tested-by: Michael Roth > = > > --- > > Note the commit I mentioned Cc's gnu-stable@nongnu.org. Assuming this > > patch is acceptable it probably makes sense for it to follow the other > > patch into stable too. Agreed, CC'ing stable. > > = > > qemu-char.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > = > > diff --git a/qemu-char.c b/qemu-char.c > > index 16f3ad7..1be1cf6 100644 > > --- a/qemu-char.c > > +++ b/qemu-char.c > > @@ -1142,8 +1142,8 @@ static void pty_chr_state(CharDriverState *chr, i= nt connected) > > s->timer_tag =3D 0; > > } > > if (!s->connected) { > > - qemu_chr_be_generic_open(chr); > > s->connected =3D 1; > > + qemu_chr_be_generic_open(chr); > > s->fd_tag =3D io_add_watch_poll(s->fd, pty_chr_read_poll, = pty_chr_read, chr); > > } > > } > > -- = > > 1.8.1.2