Messages in this thread | | | Date | Tue, 26 Feb 2013 08:37:44 -0800 | Subject | Re: [PATCH v2 2/3] freezer: do not send a fake signal to a PF_DUMPCORE thread | From | Mandeep Singh Baines <> |
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On Sun, Feb 24, 2013 at 10:36 AM, Oleg Nesterov <oleg@redhat.com> wrote: > A coredumping thread can't be frozen anyway but the fake signal sent > by freeze_task() can confuse dump_write/wait_for_dump_helpers/etc > and interrupt the coredump. > > We are going to make the do_coredump() paths freezable but the fake > TIF_SIGPENDING doesn't help, it only makes sense when we assume that > the target can return to user-mode and call get_signal_to_deliver(). > > Change freeze_task() to check PF_DUMPCORE along with PF_KTHREAD. We > need to recheck PF_DUMPCORE under ->siglock to avoid the race with > zap_threads() which can set this flag right before we take the lock. >
Won't this prevent suspend?
If there is a wait_event_interruptible in the coredump path, you'll wake it up but it will simply go back to sleep. So try_to_freeze_tasks will fail waiting for the coredump thread to enter the freezer.
Regards, Mandeep
> Signed-off-by: Oleg Nesterov <oleg@redhat.com> > --- > kernel/freezer.c | 19 ++++++++++++------- > 1 files changed, 12 insertions(+), 7 deletions(-) > > diff --git a/kernel/freezer.c b/kernel/freezer.c > index c38893b..595afab 100644 > --- a/kernel/freezer.c > +++ b/kernel/freezer.c > @@ -85,14 +85,21 @@ bool __refrigerator(bool check_kthr_stop) > } > EXPORT_SYMBOL(__refrigerator); > > -static void fake_signal_wake_up(struct task_struct *p) > +static bool fake_signal_wake_up(struct task_struct *p) > { > unsigned long flags; > + bool ret = false; > + > + if (p->flags & (PF_KTHREAD | PF_DUMPCORE)) > + return ret; > > if (lock_task_sighand(p, &flags)) { > - signal_wake_up(p, 0); > + ret = !(p->flags & PF_DUMPCORE); > + if (ret) > + signal_wake_up(p, 0); > unlock_task_sighand(p, &flags); > } > + return ret; > } > > /** > @@ -100,8 +107,8 @@ static void fake_signal_wake_up(struct task_struct *p) > * @p: task to send the request to > * > * If @p is freezing, the freeze request is sent either by sending a fake > - * signal (if it's not a kernel thread) or waking it up (if it's a kernel > - * thread). > + * signal (if it's not a kernel thread or a coredumping thread) or waking > + * it up otherwise. > * > * RETURNS: > * %false, if @p is not freezing or already frozen; %true, otherwise > @@ -116,9 +123,7 @@ bool freeze_task(struct task_struct *p) > return false; > } > > - if (!(p->flags & PF_KTHREAD)) > - fake_signal_wake_up(p); > - else > + if (!fake_signal_wake_up(p)) > wake_up_state(p, TASK_INTERRUPTIBLE); > > spin_unlock_irqrestore(&freezer_lock, flags); > -- > 1.5.5.1 > >
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