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    Subject[PATCH 3.16 269/328] bcache: add separate workqueue for journal_write to avoid deadlock
    3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Guoju Fang <fangguoju@gmail.com>

    commit 0f843e65d9eef4936929bb036c5f771fb261eea4 upstream.

    After write SSD completed, bcache schedules journal_write work to
    system_wq, which is a public workqueue in system, without WQ_MEM_RECLAIM
    flag. system_wq is also a bound wq, and there may be no idle kworker on
    current processor. Creating a new kworker may unfortunately need to
    reclaim memory first, by shrinking cache and slab used by vfs, which
    depends on bcache device. That's a deadlock.

    This patch create a new workqueue for journal_write with WQ_MEM_RECLAIM
    flag. It's rescuer thread will work to avoid the deadlock.

    Signed-off-by: Guoju Fang <fangguoju@gmail.com>
    Signed-off-by: Coly Li <colyli@suse.de>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/md/bcache/bcache.h | 1 +
    drivers/md/bcache/journal.c | 6 +++---
    drivers/md/bcache/super.c | 8 ++++++++
    3 files changed, 12 insertions(+), 3 deletions(-)

    --- a/drivers/md/bcache/bcache.h
    +++ b/drivers/md/bcache/bcache.h
    @@ -898,6 +898,7 @@ void bch_prio_write(struct cache *);
    void bch_write_bdev_super(struct cached_dev *, struct closure *);

    extern struct workqueue_struct *bcache_wq;
    +extern struct workqueue_struct *bch_journal_wq;
    extern const char * const bch_cache_modes[];
    extern struct mutex bch_register_lock;
    extern struct list_head bch_cache_sets;
    --- a/drivers/md/bcache/journal.c
    +++ b/drivers/md/bcache/journal.c
    @@ -454,7 +454,7 @@ static void do_journal_discard(struct ca

    closure_get(&ca->set->cl);
    INIT_WORK(&ja->discard_work, journal_discard_work);
    - schedule_work(&ja->discard_work);
    + queue_work(bch_journal_wq, &ja->discard_work);
    }
    }

    @@ -559,7 +559,7 @@ static void journal_write_done(struct cl
    : &j->w[0];

    __closure_wake_up(&w->wait);
    - continue_at_nobarrier(cl, journal_write, system_wq);
    + continue_at_nobarrier(cl, journal_write, bch_journal_wq);
    }

    static void journal_write_unlock(struct closure *cl)
    @@ -592,7 +592,7 @@ static void journal_write_unlocked(struc
    spin_unlock(&c->journal.lock);

    btree_flush_write(c);
    - continue_at(cl, journal_write, system_wq);
    + continue_at(cl, journal_write, bch_journal_wq);
    return;
    }

    --- a/drivers/md/bcache/super.c
    +++ b/drivers/md/bcache/super.c
    @@ -56,6 +56,7 @@ static int bcache_major;
    static DEFINE_IDA(bcache_minor);
    static wait_queue_head_t unregister_wait;
    struct workqueue_struct *bcache_wq;
    +struct workqueue_struct *bch_journal_wq;

    #define BTREE_MAX_PAGES (256 * 1024 / PAGE_SIZE)

    @@ -2112,6 +2113,9 @@ static void bcache_exit(void)
    kobject_put(bcache_kobj);
    if (bcache_wq)
    destroy_workqueue(bcache_wq);
    + if (bch_journal_wq)
    + destroy_workqueue(bch_journal_wq);
    +
    if (bcache_major)
    unregister_blkdev(bcache_major, "bcache");
    unregister_reboot_notifier(&reboot);
    @@ -2142,6 +2146,10 @@ static int __init bcache_init(void)
    if (!bcache_wq)
    goto err;

    + bch_journal_wq = alloc_workqueue("bch_journal", WQ_MEM_RECLAIM, 0);
    + if (!bch_journal_wq)
    + goto err;
    +
    bcache_kobj = kobject_create_and_add("bcache", fs_kobj);
    if (!bcache_kobj)
    goto err;
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