freezer: restructure __refrigerator()

If another freeze happens before all tasks leave FROZEN state after
being thawed, the freezer can see the existing FROZEN and consider the
tasks to be frozen but they can clear FROZEN without checking the new
freezing().

Oleg suggested restructuring __refrigerator() such that there's single
condition check section inside freezer_lock and sigpending is cleared
afterwards, which fixes the problem and simplifies the code.
Restructure accordingly.

-v2: Frozen loop exited without releasing freezer_lock.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>

diff --git a/kernel/freezer.c b/kernel/freezer.c
index b1e7a7b3d2cd60d02587b7e31f2c233edf791978..c3496c6a91b2c447173b30e360e3a89352e69b87 100644 (file)
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -52,39 +52,29 @@ bool __refrigerator(bool check_kthr_stop)
        /* Hmm, should we be allowed to suspend when there are realtime
           processes around? */
        bool was_frozen = false;
-       long save;
+       long save = current->state;
 
-       /*
-        * No point in checking freezing() again - the caller already did.
-        * Proceed to enter FROZEN.
-        */
-       spin_lock_irq(&freezer_lock);
-repeat:
-       current->flags |= PF_FROZEN;
-       spin_unlock_irq(&freezer_lock);
-
-       save = current->state;
        pr_debug("%s entered refrigerator\n", current->comm);
 
-       spin_lock_irq(&current->sighand->siglock);
-       recalc_sigpending(); /* We sent fake signal, clean it up */
-       spin_unlock_irq(&current->sighand->siglock);
-
        for (;;) {
                set_current_state(TASK_UNINTERRUPTIBLE);
+
+               spin_lock_irq(&freezer_lock);
+               current->flags |= PF_FROZEN;
                if (!freezing(current) ||
                    (check_kthr_stop && kthread_should_stop()))
+                       current->flags &= ~PF_FROZEN;
+               spin_unlock_irq(&freezer_lock);
+
+               if (!(current->flags & PF_FROZEN))
                        break;
                was_frozen = true;
                schedule();
        }
 
-       /* leave FROZEN */
-       spin_lock_irq(&freezer_lock);
-       if (freezing(current))
-               goto repeat;
-       current->flags &= ~PF_FROZEN;
-       spin_unlock_irq(&freezer_lock);
+       spin_lock_irq(&current->sighand->siglock);
+       recalc_sigpending(); /* We sent fake signal, clean it up */
+       spin_unlock_irq(&current->sighand->siglock);
 
        pr_debug("%s left refrigerator\n", current->comm);