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    SubjectRe: [PATCH 1/2] bdi: make sure congestion states are clear on free
    On Fri 02-02-18 09:53:28, Tejun Heo wrote:
    > FUSE has a bug where it fails to clear congestion states if a
    > connection gets aborted while congested, which can leave
    > nr_wb_congested[] stuck until reboot causing wait_iff_congested() to
    > wait spuriously.
    >
    > While the bdi owner, FUSE, is primarily responsible for clearing
    > congestion states before destroying bdi_writebacks, bdi layer can
    > ensure that congestion states are not leaked beyond bdi_writeback
    > lifecycle.
    >
    > Signed-off-by: Tejun Heo <tj@kernel.org>
    > Reported-by: Joshua Miller <joshmiller@fb.com>
    > Cc: Johannes Weiner <hannes@cmpxchg.org>
    > Cc: Jan Kara <jack@suse.cz>
    > Cc: stable@vger.kernel.org

    Looks good. You can add:

    Reviewed-by: Jan Kara <jack@suse.cz>

    Honza

    > ---
    > include/linux/backing-dev.h | 14 +++++++++++++-
    > mm/backing-dev.c | 2 +-
    > 2 files changed, 14 insertions(+), 2 deletions(-)
    >
    > --- a/include/linux/backing-dev.h
    > +++ b/include/linux/backing-dev.h
    > @@ -220,6 +220,18 @@ static inline int bdi_sched_wait(void *w
    > return 0;
    > }
    >
    > +static inline void __wb_congested_free(struct bdi_writeback_congested *congested)
    > +{
    > + /*
    > + * Make sure congestion states are cleared before freeing to avoid
    > + * nr_wb_congested() corruption which can lead to misbehaving
    > + * wait_iff_congested().
    > + */
    > + clear_wb_congested(congested, BLK_RW_SYNC);
    > + clear_wb_congested(congested, BLK_RW_ASYNC);
    > + kfree(congested);
    > +}
    > +
    > #ifdef CONFIG_CGROUP_WRITEBACK
    >
    > struct bdi_writeback_congested *
    > @@ -409,7 +421,7 @@ wb_congested_get_create(struct backing_d
    > static inline void wb_congested_put(struct bdi_writeback_congested *congested)
    > {
    > if (atomic_dec_and_test(&congested->refcnt))
    > - kfree(congested);
    > + __wb_congested_free(congested);
    > }
    >
    > static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
    > --- a/mm/backing-dev.c
    > +++ b/mm/backing-dev.c
    > @@ -509,7 +509,7 @@ void wb_congested_put(struct bdi_writeba
    > }
    >
    > spin_unlock_irqrestore(&cgwb_lock, flags);
    > - kfree(congested);
    > + __wb_congested_free(congested);
    > }
    >
    > static void cgwb_release_workfn(struct work_struct *work)
    --
    Jan Kara <jack@suse.com>
    SUSE Labs, CR

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