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    SubjectRe: [PATCH block/for-linus] block: don't release bdi while request_queue has live references
    Date
    Tejun Heo <tj@kernel.org> writes:

    [snip]

    Thanks for the nice write-up of the problem. This looks good to me.
    The only minor nit I have is that you might want to rename
    cgwb_bdi_destroy to cgwb_bdi_unregister.

    Reviewed-by: Jeff Moyer <jmoyer@redhat.com>


    > Signed-off-by: Tejun Heo <tj@kernel.org>
    > Fixes: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback")
    > Cc: stable@vger.kernel.org # v4.2+
    > Reported-and-tested-by: Andrey Konovalov <andreyknvl@google.com>
    > Link: http://lkml.kernel.org/g/CAAeHK+zUJ74Zn17=rOyxacHU18SgCfC6bsYW=6kCY5GXJBwGfQ@mail.gmail.com
    > ---
    > block/blk-core.c | 2 +-
    > block/blk-sysfs.c | 1 +
    > include/linux/backing-dev.h | 6 +++++-
    > mm/backing-dev.c | 12 +++++++++++-
    > 4 files changed, 18 insertions(+), 3 deletions(-)
    >
    > diff --git a/block/blk-core.c b/block/blk-core.c
    > index 60912e9..ae49240 100644
    > --- a/block/blk-core.c
    > +++ b/block/blk-core.c
    > @@ -576,7 +576,7 @@ void blk_cleanup_queue(struct request_queue *q)
    > q->queue_lock = &q->__queue_lock;
    > spin_unlock_irq(lock);
    >
    > - bdi_destroy(&q->backing_dev_info);
    > + bdi_unregister(&q->backing_dev_info);
    >
    > /* @q is and will stay empty, shutdown and put */
    > blk_put_queue(q);
    > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
    > index 3e44a9d..07b42f5 100644
    > --- a/block/blk-sysfs.c
    > +++ b/block/blk-sysfs.c
    > @@ -540,6 +540,7 @@ static void blk_release_queue(struct kobject *kobj)
    > struct request_queue *q =
    > container_of(kobj, struct request_queue, kobj);
    >
    > + bdi_exit(&q->backing_dev_info);
    > blkcg_exit_queue(q);
    >
    > if (q->elevator) {
    > diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
    > index 0fe9df9..fe0ab98 100644
    > --- a/include/linux/backing-dev.h
    > +++ b/include/linux/backing-dev.h
    > @@ -18,13 +18,17 @@
    > #include <linux/slab.h>
    >
    > int __must_check bdi_init(struct backing_dev_info *bdi);
    > -void bdi_destroy(struct backing_dev_info *bdi);
    > +void bdi_exit(struct backing_dev_info *bdi);
    >
    > __printf(3, 4)
    > int bdi_register(struct backing_dev_info *bdi, struct device *parent,
    > const char *fmt, ...);
    > int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
    > +void bdi_unregister(struct backing_dev_info *bdi);
    > +
    > int __must_check bdi_setup_and_register(struct backing_dev_info *, char *);
    > +void bdi_destroy(struct backing_dev_info *bdi);
    > +
    > void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
    > bool range_cyclic, enum wb_reason reason);
    > void wb_start_background_writeback(struct bdi_writeback *wb);
    > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
    > index dac5bf5..dc07d88 100644
    > --- a/mm/backing-dev.c
    > +++ b/mm/backing-dev.c
    > @@ -823,7 +823,7 @@ static void bdi_remove_from_list(struct backing_dev_info *bdi)
    > synchronize_rcu_expedited();
    > }
    >
    > -void bdi_destroy(struct backing_dev_info *bdi)
    > +void bdi_unregister(struct backing_dev_info *bdi)
    > {
    > /* make sure nobody finds us on the bdi_list anymore */
    > bdi_remove_from_list(bdi);
    > @@ -835,9 +835,19 @@ void bdi_destroy(struct backing_dev_info *bdi)
    > device_unregister(bdi->dev);
    > bdi->dev = NULL;
    > }
    > +}
    >
    > +void bdi_exit(struct backing_dev_info *bdi)
    > +{
    > + WARN_ON_ONCE(bdi->dev);
    > wb_exit(&bdi->wb);
    > }
    > +
    > +void bdi_destroy(struct backing_dev_info *bdi)
    > +{
    > + bdi_unregister(bdi);
    > + bdi_exit(bdi);
    > +}
    > EXPORT_SYMBOL(bdi_destroy);
    >
    > /*
    > --
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