lkml.org 
[lkml]   [2007]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: freezer problems
    Date
    On Wednesday, 21 February 2007 21:03, Oleg Nesterov wrote:
    > On 02/21, Rafael J. Wysocki wrote:
    > >
    > > On Wednesday, 21 February 2007 19:14, Paul E. McKenney wrote:
    > > > On Tue, Feb 20, 2007 at 07:29:01PM +0100, Rafael J. Wysocki wrote:
    > > > > On Tuesday, 20 February 2007 01:32, Rafael J. Wysocki wrote:
    > > > > > On Tuesday, 20 February 2007 01:12, Oleg Nesterov wrote:
    > > > > > Hm. In the case discussed above we have a task that's right before calling
    > > > > > frozen_process(), so we can't thaw it, because it's not frozen. It will be
    > > > > > frozen just in a while, but try_to_freeze_tasks() and thaw_tasks() have no
    > > > > > way to check this.
    > > > > >
    > > > > > I think to close this race the refrigerator should check TIF_FREEZE and set
    > > > > > PF_FROZEN _and_ reset TIF_FREEZE under a lock
    >
    > I personally think this is good. Not only this allows us to close the race,
    > I think we can do more.
    >
    > > that would also have to be
    > > > > > taken by try_to_freeze_tasks() in the beginning of the error path. This will
    > > > > > ensure that all tasks either freeze themselves before the error path in
    > > > > > try_to_freeze_tasks() is executed, or remain unfrozen.
    >
    > How about take this lock in thaw_tasks() instead/too ?

    Good point. If we take it in thaw_tasks(), then the tasks that have
    TIF_FREEZE set, but haven't entered the refrigerator yet, won't be able to
    enter the refrigerator until thaw_tasks() releases the lock ...
    >
    > Currently we need a separate loop in thaw_tasks() to handle PF_FREEZER_SKIP. This
    > means that PF_FREEZER_SKIP is not so generic: thaw_tasks() can't tolerate if such
    > a task was woken in between. What if we change thaw_process() to clear TIF_FREEZE ?

    ... and then we can drop the PF_FREEZER_SKIP-handling loop and change
    thaw_process() to clear TIF_FREEZE.

    > Note also that we can use task_lock() instead of global refrigerator_lock. This
    > means that thaw_process() should take it too, probably this is slowdown, but I
    > think not too much because thaw_process() is going to write to p->flags anyway.
    > In this case thaw_process() works perfectly as cancel_freezing_and_thaw() and
    > can be used to fix exec/coredump in future.

    Hm, I think we can try doing this too.

    I'll try to prepare a patch later today.

    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/

    \
     
     \ /
      Last update: 2007-02-21 21:55    [W:0.026 / U:209.840 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site