From 37a222f59b4bb6836ec2e3b297cae33ceac7c963 Mon Sep 17 00:00:00 2001 Message-Id: <37a222f59b4bb6836ec2e3b297cae33ceac7c963.1368111914.git.minovotn@redhat.com> In-Reply-To: <405603258af5154387bea676be1f904b6713f6ae.1368111913.git.minovotn@redhat.com> References: <405603258af5154387bea676be1f904b6713f6ae.1368111913.git.minovotn@redhat.com> From: Amit Shah Date: Wed, 24 Apr 2013 08:18:37 +0200 Subject: [PATCH 63/65] qemu-char: do not operate on sources from finalize callbacks RH-Author: Amit Shah Message-id: Patchwork-id: 50841 O-Subject: [RHEL6.5 qemu-kvm PATCH 63/65] qemu-char: do not operate on sources from finalize callbacks Bugzilla: 909059 RH-Acked-by: Hans de Goede RH-Acked-by: Gerd Hoffmann RH-Acked-by: Paolo Bonzini From: Paolo Bonzini Due to a glib bug, the finalize callback is called with the GMainContext lock held. Thus, any operation on the context from the callback will cause recursive locking and a deadlock. This happens, for example, when a client disconnects from a socket chardev. The fix for this is somewhat ugly, because we need to forego polymorphism and implement our own function to destroy IOWatchPoll sources. The right thing to do here would be child sources, but we support older glib versions that do not have them. Not coincidentially, glib developers found and fixed the deadlock as part of implementing child sources. Signed-off-by: Paolo Bonzini Tested-by: Sander Eikelenboom Message-id: 1366385529-10329-5-git-send-email-pbonzini@redhat.com Signed-off-by: Anthony Liguori (cherry picked from commit 2b316774f60291f57ca9ecb6a9f0712c532cae34) Signed-off-by: Amit Shah Conflicts: qemu-char.c --- qemu-char.c | 55 ++++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 40 insertions(+), 15 deletions(-) Signed-off-by: Michal Novotny --- qemu-char.c | 55 ++++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 40 insertions(+), 15 deletions(-) diff --git a/qemu-char.c b/qemu-char.c index 4db0a22..f02706d 100644 --- a/qemu-char.c +++ b/qemu-char.c @@ -590,12 +590,18 @@ static gboolean io_watch_poll_dispatch(GSource *source, GSourceFunc callback, static void io_watch_poll_finalize(GSource *source) { + /* Due to a glib bug, removing the last reference to a source + * inside a finalize callback causes recursive locking (and a + * deadlock). This is not a problem inside other callbacks, + * including dispatch callbacks, so we call io_remove_watch_poll + * to remove this source. At this point, iwp->src must + * be NULL, or we would leak it. + * + * This would be solved much more elegantly by child sources, + * but we support older glib versions that do not have them. + */ IOWatchPoll *iwp = io_watch_poll_from_source(source); - if (iwp->src) { - g_source_destroy(iwp->src); - g_source_unref(iwp->src); - iwp->src = NULL; - } + assert(iwp->src == NULL); } static GSourceFuncs io_watch_poll_funcs = { @@ -626,6 +632,25 @@ static guint io_add_watch_poll(GIOChannel *channel, return tag; } +static void io_remove_watch_poll(guint tag) +{ + GSource *source; + IOWatchPoll *iwp; + + g_return_if_fail (tag > 0); + + source = g_main_context_find_source_by_id(NULL, tag); + g_return_if_fail (source != NULL); + + iwp = io_watch_poll_from_source(source); + if (iwp->src) { + g_source_destroy(iwp->src); + g_source_unref(iwp->src); + iwp->src = NULL; + } + g_source_destroy(&iwp->parent); +} + static GIOChannel *io_channel_from_fd(int fd) { GIOChannel *chan; @@ -731,7 +756,7 @@ static gboolean fd_chr_read(GIOChannel *chan, GIOCondition cond, void *opaque) len, &bytes_read, NULL); if (status == G_IO_STATUS_EOF) { if (s->fd_in_tag) { - g_source_remove(s->fd_in_tag); + io_remove_watch_poll(s->fd_in_tag); s->fd_in_tag = 0; } qemu_chr_be_event(chr, CHR_EVENT_CLOSED); @@ -764,7 +789,7 @@ static void fd_chr_update_read_handler(CharDriverState *chr) FDCharDriver *s = chr->opaque; if (s->fd_in_tag) { - g_source_remove(s->fd_in_tag); + io_remove_watch_poll(s->fd_in_tag); s->fd_in_tag = 0; } @@ -778,7 +803,7 @@ static void fd_chr_close(struct CharDriverState *chr) FDCharDriver *s = chr->opaque; if (s->fd_in_tag) { - g_source_remove(s->fd_in_tag); + io_remove_watch_poll(s->fd_in_tag); s->fd_in_tag = 0; } @@ -1090,7 +1115,7 @@ static void pty_chr_state(CharDriverState *chr, int connected) if (!connected) { if (s->fd_tag) { - g_source_remove(s->fd_tag); + io_remove_watch_poll(s->fd_tag); s->fd_tag = 0; } s->connected = 0; @@ -1118,7 +1143,7 @@ static void pty_chr_close(struct CharDriverState *chr) int fd; if (s->fd_tag) { - g_source_remove(s->fd_tag); + io_remove_watch_poll(s->fd_tag); s->fd_tag = 0; } fd = g_io_channel_unix_get_fd(s->fd); @@ -2021,7 +2046,7 @@ static gboolean udp_chr_read(GIOChannel *chan, GIOCondition cond, void *opaque) s->bufptr = s->bufcnt; if (status != G_IO_STATUS_NORMAL) { if (s->tag) { - g_source_remove(s->tag); + io_remove_watch_poll(s->tag); s->tag = 0; } return FALSE; @@ -2042,7 +2067,7 @@ static void udp_chr_update_read_handler(CharDriverState *chr) NetCharDriver *s = chr->opaque; if (s->tag) { - g_source_remove(s->tag); + io_remove_watch_poll(s->tag); s->tag = 0; } @@ -2055,7 +2080,7 @@ static void udp_chr_close(CharDriverState *chr) { NetCharDriver *s = chr->opaque; if (s->tag) { - g_source_remove(s->tag); + io_remove_watch_poll(s->tag); s->tag = 0; } if (s->chan) { @@ -2282,7 +2307,7 @@ static gboolean tcp_chr_read(GIOChannel *chan, GIOCondition cond, void *opaque) s->listen_tag = g_io_add_watch(s->listen_chan, G_IO_IN, tcp_chr_accept, chr); } if (s->tag) { - g_source_remove(s->tag); + io_remove_watch_poll(s->tag); s->tag = 0; } g_io_channel_unref(s->chan); @@ -2384,7 +2409,7 @@ static void tcp_chr_close(CharDriverState *chr) TCPCharDriver *s = chr->opaque; if (s->fd >= 0) { if (s->tag) { - g_source_remove(s->tag); + io_remove_watch_poll(s->tag); s->tag = 0; } if (s->chan) { -- 1.7.11.7