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Re: [Qemu-devel] [PATCH] monitor: fix dangling CPU pointer
From: |
Greg Kurz |
Subject: |
Re: [Qemu-devel] [PATCH] monitor: fix dangling CPU pointer |
Date: |
Mon, 16 Oct 2017 17:59:25 +0200 |
On Mon, 16 Oct 2017 16:31:07 +0200
Igor Mammedov <address@hidden> wrote:
> On Mon, 16 Oct 2017 13:24:20 +0200
> Greg Kurz <address@hidden> wrote:
>
> > On Mon, 16 Oct 2017 10:41:39 +0200
> > Igor Mammedov <address@hidden> wrote:
> >
> > > On Fri, 13 Oct 2017 13:47:51 +0200
> > > Greg Kurz <address@hidden> wrote:
> > >
> > > [...]
> > >
> > > > Note that the resolution should really return a CPU object, otherwise
> > > > we have a bug. This is achieved by relying on object_resolve_path()
> > > > and CPU() instead of calling object_resolve_path_type(path, TYPE_CPU).
> > > >
> > > I'm not sure what you are trying to say here, could you explain
> > > a bit more why CPU(object_resolve_path()) is chosen vs
> > > object_resolve_path_type(path, TYPE_CPU)
> > >
> >
> > IIUC, if we use object_resolve_path_type(path, TYPE_CPU) and path doesn't
> > point to a CPU object, it will return NULL (see object_resolve_abs_path())
> > just like if the CPU got hot-unplugged.
> >
> > My point is that the path we got from object_get_canonical_path() did
> > point to a CPU: if later on this path resolves to an object that isn't
> > a CPU, then some code somewhere used the same QOM path for some unrelated
> > object. I tend to think this is a bug in QEMU and we shouldn't silently
> > ignore it.
> sometimes QOM path to a cpu object could be:
> 1. arbitrary if set explicitly by board
> 2. /unattached/device[X] or /peripheral-anon/device[X]
> potentially might end-up with another device at the same path
> in case of hot-remove + migration
> 3. /peripheral
> hot-remove named (i.e. non null 'id') cpu and then plug a non cpu
> device with the same 'id',
> which is legitimate thing to do
>
Ok, I didn't think of these cases...
> I'd use object_resolve_path_type(path, TYPE_CPU) and
> gracefully error out in case it returns NULL.
>
I'll do that. Thanks for the detailed explanation.
> > Makes sense ?
> >
> > >
> > > > Suggested-by: Igor Mammedov <address@hidden>
> > > > Signed-off-by: Greg Kurz <address@hidden>
> > > > ---
> > > > monitor.c | 25 ++++++++++++++++++++-----
> > > > 1 file changed, 20 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/monitor.c b/monitor.c
> > > > index fe0d1bdbb461..8489b2ad99c0 100644
> > > > --- a/monitor.c
> > > > +++ b/monitor.c
> > > > @@ -200,7 +200,7 @@ struct Monitor {
> > > >
> > > > ReadLineState *rs;
> > > > MonitorQMP qmp;
> > > > - CPUState *mon_cpu;
> > > > + gchar *mon_cpu_path;
> > > > BlockCompletionFunc *password_completion_cb;
> > > > void *password_opaque;
> > > > mon_cmd_t *cmd_table;
> > > > @@ -579,6 +579,7 @@ static void monitor_data_init(Monitor *mon)
> > > >
> > > > static void monitor_data_destroy(Monitor *mon)
> > > > {
> > > > + g_free(mon->mon_cpu_path);
> > > > qemu_chr_fe_deinit(&mon->chr, false);
> > > > if (monitor_is_qmp(mon)) {
> > > > json_message_parser_destroy(&mon->qmp.parser);
> > > > @@ -1047,20 +1048,34 @@ int monitor_set_cpu(int cpu_index)
> > > > if (cpu == NULL) {
> > > > return -1;
> > > > }
> > > > - cur_mon->mon_cpu = cpu;
> > > > + g_free(cur_mon->mon_cpu_path);
> > > > + cur_mon->mon_cpu_path = object_get_canonical_path(OBJECT(cpu));
> > > > return 0;
> > > > }
> > > >
> > > > CPUState *mon_get_cpu(void)
> > > > {
> > > > - if (!cur_mon->mon_cpu) {
> > > > + CPUState *cpu;
> > > > +
> > > > + if (cur_mon->mon_cpu_path) {
> > > > + Object *obj = object_resolve_path(cur_mon->mon_cpu_path, NULL);
> > > > +
> > > > + if (!obj) {
> > > > + g_free(cur_mon->mon_cpu_path);
> > > > + cur_mon->mon_cpu_path = NULL;
> > > > + } else {
> > > > + cpu = CPU(obj);
> > > this potentially might abort if obj couldn't be cast to TYPE_CPU
> > >
> >
> > This is deliberate... is there a case where cur_mon->mon_cpu_path would
> > legitimately point to something that isn't of type TYPE_CPU ?
> >
> > >
> > > > + }
> > > > + }
> > > > + if (!cur_mon->mon_cpu_path) {
> > > > if (!first_cpu) {
> > > > return NULL;
> > > > }
> > > > monitor_set_cpu(first_cpu->cpu_index);
> > > > + cpu = first_cpu;
> > > > }
> > > > - cpu_synchronize_state(cur_mon->mon_cpu);
> > > > - return cur_mon->mon_cpu;
> > > > + cpu_synchronize_state(cpu);
> > > > + return cpu;
> > > > }
> > > >
> > > > CPUArchState *mon_get_cpu_env(void)
> > > >
> > > >
> > >
> >
> >
>