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    SubjectRe: 2.6.35.5: hibernation broken... AGAIN
    Date
    On Thursday, December 02, 2010, KAMEZAWA Hiroyuki wrote:
    > On Wed, 1 Dec 2010 23:23:31 +0100
    > "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
    >
    > > On Wednesday, December 01, 2010, Rafael J. Wysocki wrote:
    > > > On Wednesday, December 01, 2010, KAMEZAWA Hiroyuki wrote:
    > > > > On Wed, 1 Dec 2010 01:38:53 +0100
    > > > > "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
    > > > >
    > > > > > On Wednesday, December 01, 2010, Rafael J. Wysocki wrote:
    > > > > > > On Tuesday, November 30, 2010, Hugh Dickins wrote:
    > > > > > > > On Sat, 27 Nov 2010, Rafael J. Wysocki wrote:
    > > > > > > > > On Saturday, November 27, 2010, Ondrej Zary wrote:
    > > > > > ...
    > > > > > > >
    > > > > > > > Trivial point, I suppose, but it bothers me that PM is accumulating
    > > > > > > > wrappers around wrappers around gfp_allowed_mask. Looks like
    > > > > > > > clear_gfp_allowed_mask and set_gfp_allowed_mask (oddly asymmetrical)
    > > > > > > > were not really what we need. How about scrapping them, and putting
    > > > > > > > pm_restrict_gfp_mask() and pm_restore_gfp_mask() into page_alloc.c?
    > > > > > >
    > > > > > > Sure, that sounds like a good idea indeed.
    > > > > >
    > > > > > Below is an updated patch in which I tried to address your comments.
    > > > > >
    > > > > > I didn't find it very useful to couple pm_restore_gfp_mask() with the thawing
    > > > > > of tasks, but nevertheless I think all of the spots where it's needed are
    > > > > > covered now.
    > > > > >
    > > > > > The patch has only been compile-tested for now, so caveat emptor.
    > > > > >
    > > > >
    > > > > Hmm, can't we have some error check as
    > > > >
    > > > > > +static gfp_t saved_gfp_mask;
    > > > >
    > > > > atomic_t gfp_mask_save_mode_counter;
    > > > >
    > > > > > +
    > > > > > +void pm_restore_gfp_mask(void)
    > > > > > {
    > > > > > WARN_ON(!mutex_is_locked(&pm_mutex));
    > > > > > - gfp_allowed_mask = mask;
    > > > >
    > > > > if (atomic_dec_return(&gfp_mask_save_mode_counter))
    > > > > WARN_ONCE()
    > > > >
    > > > > > + if (saved_gfp_mask) {
    > > > > > + gfp_allowed_mask = saved_gfp_mask;
    > > > > > + saved_gfp_mask = 0;
    > > > > > + }
    > > > > > }
    > > > >
    > > > > > +void pm_restrict_gfp_mask(void)
    > > > > > {
    > > > > > - gfp_t ret = gfp_allowed_mask;
    > > > > > -
    > > > > > WARN_ON(!mutex_is_locked(&pm_mutex));
    > > > > > - gfp_allowed_mask &= ~mask;
    > > > > > - return ret;
    > > > > > + saved_gfp_mask = gfp_allowed_mask;
    > > > > > + gfp_allowed_mask &= ~GFP_IOFS;
    > > > >
    > > > > if (atomic_inc_return(&gfp_mask_save_mode_counter) > 1)
    > > > > WARN_ONCE()
    > > > >
    > > > > or some ?
    > > >
    > > > What exactly would that be useful for?
    > >
    > > Please note that pm_restore_gfp_mask() can be legitimately called before
    > > pm_restrict_gfp_mask() via the SNAPSHOT_CREATE_IMAGE hibernate ioctl, so the
    > > test you're suggesting wouldn't really work.
    > >
    >
    > Hm, I just wonder some tests not for breaking gfp_allowed_mask by
    > - double call

    That's easy. It's sufficient to do WARN_ON(saved_gfp_mask) at the beginning
    of pm_restrict_gfp_mask(). This also takes care of the "forget to restore"
    case to some extent, because pm_restrict_gfp_mask() will generally be only
    called twice in a row if there's a missing pm_restore_gfp_mask() in between.

    > - forget to restore

    This is kind of difficult in general. You can't detect a missing
    pm_restore_gfp_mask() other than by checking if pm_restrict_gfp_mask() is not
    called twice in a row IMHO.

    > That will be fatal.

    Yes, it will.

    > I'm not very interested in implementation detail

    Well ...

    Thanks,
    Rafael


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