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    Subject[PATCH 06/17] fs: icache lock lru/writeback lists
    Date
    From: Nick Piggin <npiggin@suse.de>

    The inode moves between different lists protected by the inode_lock. Introduce
    a new lock that protects all of the lists (dirty, unused, in use, etc) that the
    inode will move around as it changes state. As this is mostly a list for
    protecting the writeback lists, name it wb_inode_list_lock and nest all the
    list manipulations in this lock inside the current inode_lock scope.

    Signed-off-by: Nick Piggin <npiggin@suse.de>
    Signed-off-by: Dave Chinner <dchinner@redhat.com>
    ---
    fs/fs-writeback.c | 48 +++++++++++++++++++++++++++++++++++++++++++-
    fs/inode.c | 44 +++++++++++++++++++++++++++++++++-------
    include/linux/writeback.h | 1 +
    mm/backing-dev.c | 4 +++
    4 files changed, 87 insertions(+), 10 deletions(-)

    diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
    index 2edaad7..fb7b723 100644
    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -161,6 +161,7 @@ static void redirty_tail(struct inode *inode)
    {
    struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

    + assert_spin_locked(&wb_inode_list_lock);
    if (!list_empty(&wb->b_dirty)) {
    struct inode *tail;

    @@ -178,6 +179,7 @@ static void requeue_io(struct inode *inode)
    {
    struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

    + assert_spin_locked(&wb_inode_list_lock);
    list_move(&inode->i_list, &wb->b_more_io);
    }

    @@ -218,6 +220,7 @@ static void move_expired_inodes(struct list_head *delaying_queue,
    struct inode *inode;
    int do_sb_sort = 0;

    + assert_spin_locked(&wb_inode_list_lock);
    while (!list_empty(delaying_queue)) {
    inode = list_entry(delaying_queue->prev, struct inode, i_list);
    if (older_than_this &&
    @@ -281,11 +284,13 @@ static void inode_wait_for_writeback(struct inode *inode)

    wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
    while (inode->i_state & I_SYNC) {
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lock);
    __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
    spin_lock(&inode_lock);
    spin_lock(&inode->i_lock);
    + spin_lock(&wb_inode_list_lock);
    }
    }

    @@ -339,6 +344,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
    /* Set I_SYNC, reset I_DIRTY_PAGES */
    inode->i_state |= I_SYNC;
    inode->i_state &= ~I_DIRTY_PAGES;
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lock);

    @@ -375,6 +381,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)

    spin_lock(&inode_lock);
    spin_lock(&inode->i_lock);
    + spin_lock(&wb_inode_list_lock);
    inode->i_state &= ~I_SYNC;
    if (!(inode->i_state & I_FREEING)) {
    if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
    @@ -461,11 +468,18 @@ static bool pin_sb_for_writeback(struct super_block *sb)
    static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
    struct writeback_control *wbc, bool only_this_sb)
    {
    +again:
    while (!list_empty(&wb->b_io)) {
    long pages_skipped;
    struct inode *inode = list_entry(wb->b_io.prev,
    struct inode, i_list);

    + if (!spin_trylock(&inode->i_lock)) {
    + spin_unlock(&wb_inode_list_lock);
    + spin_lock(&wb_inode_list_lock);
    + goto again;
    + }
    +
    if (inode->i_sb != sb) {
    if (only_this_sb) {
    /*
    @@ -474,9 +488,12 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
    * to it back onto the dirty list.
    */
    redirty_tail(inode);
    + spin_unlock(&inode->i_lock);
    continue;
    }

    + spin_unlock(&inode->i_lock);
    +
    /*
    * The inode belongs to a different superblock.
    * Bounce back to the caller to unpin this and
    @@ -485,10 +502,9 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
    return 0;
    }

    - spin_lock(&inode->i_lock);
    if (inode->i_state & (I_NEW | I_WILL_FREE)) {
    - spin_unlock(&inode->i_lock);
    requeue_io(inode);
    + spin_unlock(&inode->i_lock);
    continue;
    }
    /*
    @@ -511,11 +527,13 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
    */
    redirty_tail(inode);
    }
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lock);
    iput(inode);
    cond_resched();
    spin_lock(&inode_lock);
    + spin_lock(&wb_inode_list_lock);
    if (wbc->nr_to_write <= 0) {
    wbc->more_io = 1;
    return 1;
    @@ -535,6 +553,9 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
    if (!wbc->wb_start)
    wbc->wb_start = jiffies; /* livelock avoidance */
    spin_lock(&inode_lock);
    +again:
    + spin_lock(&wb_inode_list_lock);
    +
    if (!wbc->for_kupdate || list_empty(&wb->b_io))
    queue_io(wb, wbc->older_than_this);

    @@ -544,7 +565,12 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
    struct super_block *sb = inode->i_sb;

    if (!pin_sb_for_writeback(sb)) {
    + if (!spin_trylock(&inode->i_lock)) {
    + spin_unlock(&wb_inode_list_lock);
    + goto again;
    + }
    requeue_io(inode);
    + spin_unlock(&inode->i_lock);
    continue;
    }
    ret = writeback_sb_inodes(sb, wb, wbc, false);
    @@ -553,6 +579,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
    if (ret)
    break;
    }
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode_lock);
    /* Leave any unwritten inodes on b_io */
    }
    @@ -563,9 +590,11 @@ static void __writeback_inodes_sb(struct super_block *sb,
    WARN_ON(!rwsem_is_locked(&sb->s_umount));

    spin_lock(&inode_lock);
    + spin_lock(&wb_inode_list_lock);
    if (!wbc->for_kupdate || list_empty(&wb->b_io))
    queue_io(wb, wbc->older_than_this);
    writeback_sb_inodes(sb, wb, wbc, true);
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode_lock);
    }

    @@ -676,13 +705,22 @@ static long wb_writeback(struct bdi_writeback *wb,
    * become available for writeback. Otherwise
    * we'll just busyloop.
    */
    +retry:
    spin_lock(&inode_lock);
    + spin_lock(&wb_inode_list_lock);
    if (!list_empty(&wb->b_more_io)) {
    inode = list_entry(wb->b_more_io.prev,
    struct inode, i_list);
    + if (!spin_trylock(&inode->i_lock)) {
    + spin_unlock(&wb_inode_list_lock);
    + spin_unlock(&inode_lock);
    + goto retry;
    + }
    trace_wbc_writeback_wait(&wbc, wb->bdi);
    inode_wait_for_writeback(inode);
    + spin_unlock(&inode->i_lock);
    }
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode_lock);
    }

    @@ -993,8 +1031,10 @@ void __mark_inode_dirty(struct inode *inode, int flags)
    wakeup_bdi = true;
    }

    + spin_lock(&wb_inode_list_lock);
    inode->dirtied_when = jiffies;
    list_move(&inode->i_list, &bdi->wb.b_dirty);
    + spin_unlock(&wb_inode_list_lock);
    }
    }
    out:
    @@ -1183,7 +1223,9 @@ int write_inode_now(struct inode *inode, int sync)
    might_sleep();
    spin_lock(&inode_lock);
    spin_lock(&inode->i_lock);
    + spin_lock(&wb_inode_list_lock);
    ret = writeback_single_inode(inode, &wbc);
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lock);
    if (sync)
    @@ -1209,7 +1251,9 @@ int sync_inode(struct inode *inode, struct writeback_control *wbc)

    spin_lock(&inode_lock);
    spin_lock(&inode->i_lock);
    + spin_lock(&wb_inode_list_lock);
    ret = writeback_single_inode(inode, wbc);
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lock);
    return ret;
    diff --git a/fs/inode.c b/fs/inode.c
    index 2e8ab8e..e15620f 100644
    --- a/fs/inode.c
    +++ b/fs/inode.c
    @@ -31,6 +31,8 @@
    * s_inodes, i_sb_list
    * inode_hash_lock protects:
    * inode hash table, i_hash
    + * wb_inode_list_lock protects:
    + * inode_in_use, inode_unused, b_io, b_more_io, b_dirty, i_list
    * inode->i_lock protects:
    * i_state, i_count
    *
    @@ -38,6 +40,7 @@
    * inode_lock
    * sb_inode_list_lock
    * inode->i_lock
    + * wb_inode_list_lock
    * inode_hash_lock
    */
    /*
    @@ -99,6 +102,7 @@ static struct hlist_head *inode_hashtable __read_mostly;
    */
    DEFINE_SPINLOCK(inode_lock);
    DEFINE_SPINLOCK(sb_inode_list_lock);
    +DEFINE_SPINLOCK(wb_inode_list_lock);
    DEFINE_SPINLOCK(inode_hash_lock);

    /*
    @@ -304,8 +308,11 @@ void __iget(struct inode *inode)
    if (inode->i_count > 1)
    return;

    - if (!(inode->i_state & (I_DIRTY|I_SYNC)))
    + if (!(inode->i_state & (I_DIRTY|I_SYNC))) {
    + spin_lock(&wb_inode_list_lock);
    list_move(&inode->i_list, &inode_in_use);
    + spin_unlock(&wb_inode_list_lock);
    + }
    inodes_stat.nr_unused--;
    }

    @@ -408,7 +415,9 @@ static int invalidate_list(struct list_head *head, struct list_head *dispose)
    }
    invalidate_inode_buffers(inode);
    if (!inode->i_count) {
    + spin_lock(&wb_inode_list_lock);
    list_move(&inode->i_list, dispose);
    + spin_unlock(&wb_inode_list_lock);
    WARN_ON(inode->i_state & I_NEW);
    inode->i_state |= I_FREEING;
    spin_unlock(&inode->i_lock);
    @@ -486,6 +495,8 @@ static void prune_icache(int nr_to_scan)

    down_read(&iprune_sem);
    spin_lock(&inode_lock);
    +again:
    + spin_lock(&wb_inode_list_lock);
    for (nr_scanned = 0; nr_scanned < nr_to_scan; nr_scanned++) {
    struct inode *inode;

    @@ -494,13 +505,17 @@ static void prune_icache(int nr_to_scan)

    inode = list_entry(inode_unused.prev, struct inode, i_list);

    - spin_lock(&inode->i_lock);
    + if (!spin_trylock(&inode->i_lock)) {
    + spin_unlock(&wb_inode_list_lock);
    + goto again;
    + }
    if (inode->i_state || inode->i_count) {
    list_move(&inode->i_list, &inode_unused);
    spin_unlock(&inode->i_lock);
    continue;
    }
    if (inode_has_buffers(inode) || inode->i_data.nrpages) {
    + spin_unlock(&wb_inode_list_lock);
    __iget(inode);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lock);
    @@ -509,11 +524,16 @@ static void prune_icache(int nr_to_scan)
    0, -1);
    iput(inode);
    spin_lock(&inode_lock);
    +again2:
    + spin_lock(&wb_inode_list_lock);

    if (inode != list_entry(inode_unused.next,
    struct inode, i_list))
    continue; /* wrong inode or list_empty */
    - spin_lock(&inode->i_lock);
    + if (!spin_trylock(&inode->i_lock)) {
    + spin_unlock(&wb_inode_list_lock);
    + goto again2;
    + }
    if (!can_unuse(inode)) {
    spin_unlock(&inode->i_lock);
    continue;
    @@ -531,6 +551,7 @@ static void prune_icache(int nr_to_scan)
    else
    __count_vm_events(PGINODESTEAL, reap);
    spin_unlock(&inode_lock);
    + spin_unlock(&wb_inode_list_lock);

    dispose_list(&freeable);
    up_read(&iprune_sem);
    @@ -654,7 +675,9 @@ __inode_add_to_lists(struct super_block *sb, struct hlist_head *head,
    spin_lock(&sb_inode_list_lock);
    list_add(&inode->i_sb_list, &sb->s_inodes);
    spin_unlock(&sb_inode_list_lock);
    + spin_lock(&wb_inode_list_lock);
    list_add(&inode->i_list, &inode_in_use);
    + spin_unlock(&wb_inode_list_lock);
    if (head) {
    spin_lock(&inode_hash_lock);
    hlist_add_head(&inode->i_hash, head);
    @@ -1308,8 +1331,11 @@ static void iput_final(struct inode *inode)
    drop = generic_drop_inode(inode);

    if (!drop) {
    - if (!(inode->i_state & (I_DIRTY|I_SYNC)))
    + if (!(inode->i_state & (I_DIRTY|I_SYNC))) {
    + spin_lock(&wb_inode_list_lock);
    list_move(&inode->i_list, &inode_unused);
    + spin_unlock(&wb_inode_list_lock);
    + }
    inodes_stat.nr_unused++;
    if (sb->s_flags & MS_ACTIVE) {
    spin_unlock(&inode->i_lock);
    @@ -1333,7 +1359,9 @@ static void iput_final(struct inode *inode)
    hlist_del_init(&inode->i_hash);
    spin_unlock(&inode_hash_lock);
    }
    + spin_lock(&wb_inode_list_lock);
    list_del_init(&inode->i_list);
    + spin_unlock(&wb_inode_list_lock);
    list_del_init(&inode->i_sb_list);
    spin_unlock(&sb_inode_list_lock);
    WARN_ON(inode->i_state & I_NEW);
    @@ -1366,17 +1394,17 @@ void iput(struct inode *inode)
    if (inode) {
    BUG_ON(inode->i_state & I_CLEAR);

    -retry:
    +retry1:
    spin_lock(&inode->i_lock);
    if (inode->i_count == 1) {
    if (!spin_trylock(&inode_lock)) {
    +retry2:
    spin_unlock(&inode->i_lock);
    - goto retry;
    + goto retry1;
    }
    if (!spin_trylock(&sb_inode_list_lock)) {
    spin_unlock(&inode_lock);
    - spin_unlock(&inode->i_lock);
    - goto retry;
    + goto retry2;
    }
    inode->i_count--;
    iput_final(inode);
    diff --git a/include/linux/writeback.h b/include/linux/writeback.h
    index 35d6e81..8b9c24f 100644
    --- a/include/linux/writeback.h
    +++ b/include/linux/writeback.h
    @@ -11,6 +11,7 @@ struct backing_dev_info;

    extern spinlock_t inode_lock;
    extern spinlock_t sb_inode_list_lock;
    +extern spinlock_t wb_inode_list_lock;
    extern spinlock_t inode_hash_lock;
    extern struct list_head inode_in_use;
    extern struct list_head inode_unused;
    diff --git a/mm/backing-dev.c b/mm/backing-dev.c
    index c2bf86f..b1e2987 100644
    --- a/mm/backing-dev.c
    +++ b/mm/backing-dev.c
    @@ -73,12 +73,14 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)

    nr_wb = nr_dirty = nr_io = nr_more_io = 0;
    spin_lock(&inode_lock);
    + spin_lock(&wb_inode_list_lock);
    list_for_each_entry(inode, &wb->b_dirty, i_list)
    nr_dirty++;
    list_for_each_entry(inode, &wb->b_io, i_list)
    nr_io++;
    list_for_each_entry(inode, &wb->b_more_io, i_list)
    nr_more_io++;
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode_lock);

    global_dirty_limits(&background_thresh, &dirty_thresh);
    @@ -681,9 +683,11 @@ void bdi_destroy(struct backing_dev_info *bdi)
    struct bdi_writeback *dst = &default_backing_dev_info.wb;

    spin_lock(&inode_lock);
    + spin_lock(&wb_inode_list_lock);
    list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
    list_splice(&bdi->wb.b_io, &dst->b_io);
    list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
    + spin_unlock(&wb_inode_list_lock);
    spin_unlock(&inode_lock);
    }

    --
    1.7.1


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