Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH -mm] swsusp: freeze user space processes first | Date | Sun, 5 Feb 2006 11:34:18 +0100 |
| |
Hi,
On Sunday 05 February 2006 10:38, Andrew Morton wrote: > "Rafael J. Wysocki" <rjw@sisk.pl> wrote: > > This patch allows swsusp to freeze processes successfully under heavy load > > by freezing userspace processes before kernel threads. > > > > ... > > > > /* 0 = success, else # of processes that we failed to stop */ > > int freeze_processes(void) > > { > > - int todo; > > + int todo, nr_user, user_frozen; > > unsigned long start_time; > > struct task_struct *g, *p; > > unsigned long flags; > > > > printk( "Stopping tasks: " ); > > start_time = jiffies; > > + user_frozen = 0; > > do { > > - todo = 0; > > + nr_user = todo = 0; > > read_lock(&tasklist_lock); > > do_each_thread(g, p) { > > if (!freezeable(p)) > > continue; > > if (frozen(p)) > > continue; > > - > > - freeze(p); > > - spin_lock_irqsave(&p->sighand->siglock, flags); > > - signal_wake_up(p, 0); > > - spin_unlock_irqrestore(&p->sighand->siglock, flags); > > - todo++; > > + if (p->mm && !(p->flags & PF_BORROWED_MM)) { > > + /* The task is a user-space one. > > + * Freeze it unless there's a vfork completion > > + * pending > > + */ > > + if (!p->vfork_done) > > + freeze_process(p); > > + nr_user++; > > + } else { > > + /* Freeze only if the user space is frozen */ > > + if (user_frozen) > > + freeze_process(p); > > + todo++; > > + } > > } while_each_thread(g, p); > > read_unlock(&tasklist_lock); > > + todo += nr_user; > > + if (!user_frozen && !nr_user) { > > + sys_sync(); > > + start_time = jiffies; > > + } > > + user_frozen = !nr_user; > > yield(); /* Yield is okay here */ > > - if (todo && time_after(jiffies, start_time + TIMEOUT)) { > > - printk( "\n" ); > > - printk(KERN_ERR " stopping tasks timed out (%d tasks remaining)\n", todo ); > > + if (todo && time_after(jiffies, start_time + TIMEOUT)) > > break; > > The logic in that loop makes my brain burst. > > What happens if a process does vfork();sleep(100000000)?
The freezing of processes will fail due to the timeout.
Without the if (!p->vfork_done) it would fail too, because the child would be frozen and the parent would wait for the vfork completion in the TASK_UNINTERRUPTIBLE state (ie. unfreezeable). But in that case we have a race between the "freezer" and the child process (ie. if the child gets frozen before it completes the vfork completion, the paret will be unfreezeable) which sometimes leads to a failure when it should not. [We have a test case showing this.]
Greetings, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |