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monitor: maintain at most one G_IO_OUT watch 

When monitor_flush() is invoked repeatedly outside the monitor_unblocked()
callback, for example from tlb_info() -> ... -> print_pte(), several
watches may be added for the same event.

This is no problem per se because the extra monitor_unblocked() callbacks
are harmless if mon->outbuf is empty, the watches will be removed
gradually. However a big number of watches can grow "gpollfds" without
limit in glib_pollfds_fill(), triggering a -1/EINVAL condition in
g_poll().

Keep at most one such watch, by following the pattern observable in eg.
commits c874ea97 and c3d6b96e. The change has no effect when
monitor_unblocked() calls monitor_flush() (when the watch can either be
removed or renewed 1-for-1), but non-callback contexts won't create an
additional watch when the monitor already has one.

Related RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=970047

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1373998781-29561-3-git-send-email-lersek@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
master
Laszlo Ersek 2013-07-16 20:19:41 +02:00 committed by Anthony Liguori
parent ac8c26f633
commit 293d2a0014
1 changed files with 9 additions and 2 deletions
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11
monitor.c
View File

@ -189,6 +189,7 @@ struct Monitor {
int suspend_cnt;
bool skip_flush;
QString *outbuf;
guint watch;
ReadLineState *rs;
MonitorControl *mc;
CPUState *mon_cpu;
@ -263,7 +264,10 @@ int monitor_read_password(Monitor *mon, ReadLineFunc *readline_func,
static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond,
void *opaque)
{
monitor_flush(opaque);
Monitor *mon = opaque;
mon->watch = 0;
monitor_flush(mon);
return FALSE;
}
@ -294,7 +298,10 @@ void monitor_flush(Monitor *mon)
QDECREF(mon->outbuf);
mon->outbuf = tmp;
}
qemu_chr_fe_add_watch(mon->chr, G_IO_OUT, monitor_unblocked, mon);
if (mon->watch == 0) {
mon->watch = qemu_chr_fe_add_watch(mon->chr, G_IO_OUT,
monitor_unblocked, mon);
}
}
}