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    Subject[PATCH 4/4] fs: remove inode_lock from iput_final and prune_icache
    Date
    From: Dave Chinner <dchinner@redhat.com>

    Now that inode state changes are protected by the inode->i_lock and
    the inode LRU manipulations by the inode_lru_lock, we can remove the
    inode_lock from prune_icache and the initial part of iput_final().

    instead of using the inode_lock to protect the inode during
    iput_final, use the inode->i_lock instead. This protects the inode
    against new references being taken while we change the inode state
    to I_FREEING, as well as preventing prune_icache from grabbing the
    inode while we are manipulating it. Hence we no longer need the
    iṉode_lock in iput_final prior to setting I_FREEING on the inode.

    For prune_icache, we no longer need the inode_lock to protect the
    LRU list, and the inodes themselves are protected against freeing
    races by the inode->i_lock. Hence we can lift the inode_lock from
    prune_icache as well.

    Signed-off-by: Dave Chinner <dchinner@redhat.com>
    ---
    fs/inode.c | 19 +++++--------------
    1 files changed, 5 insertions(+), 14 deletions(-)

    diff --git a/fs/inode.c b/fs/inode.c
    index e04371e..b5f1585 100644
    --- a/fs/inode.c
    +++ b/fs/inode.c
    @@ -634,7 +634,6 @@ static void prune_icache(int nr_to_scan)
    unsigned long reap = 0;

    down_read(&iprune_sem);
    - spin_lock(&inode_lock);
    spin_lock(&inode_lru_lock);
    for (nr_scanned = 0; nr_scanned < nr_to_scan; nr_scanned++) {
    struct inode *inode;
    @@ -660,8 +659,8 @@ static void prune_icache(int nr_to_scan)
    */
    if (atomic_read(&inode->i_count) ||
    (inode->i_state & ~I_REFERENCED)) {
    - spin_unlock(&inode->i_lock);
    list_del_init(&inode->i_lru);
    + spin_unlock(&inode->i_lock);
    percpu_counter_dec(&nr_inodes_unused);
    continue;
    }
    @@ -669,20 +668,18 @@ static void prune_icache(int nr_to_scan)
    /* recently referenced inodes get one more pass */
    if (inode->i_state & I_REFERENCED) {
    inode->i_state &= ~I_REFERENCED;
    - spin_unlock(&inode->i_lock);
    list_move(&inode->i_lru, &inode_lru);
    + spin_unlock(&inode->i_lock);
    continue;
    }
    if (inode_has_buffers(inode) || inode->i_data.nrpages) {
    __iget(inode);
    spin_unlock(&inode->i_lock);
    spin_unlock(&inode_lru_lock);
    - spin_unlock(&inode_lock);
    if (remove_inode_buffers(inode))
    reap += invalidate_mapping_pages(&inode->i_data,
    0, -1);
    iput(inode);
    - spin_lock(&inode_lock);
    spin_lock(&inode_lru_lock);

    if (inode != list_entry(inode_lru.next,
    @@ -701,8 +698,8 @@ static void prune_icache(int nr_to_scan)
    spin_unlock(&inode->i_lock);

    /*
    - * Move the inode off the IO lists and LRU once I_FREEING is
    - * set so that it won't get moved back on there if it is dirty.
    + * Move the inode off the LRU once I_FREEING is set so that it
    + * won't get moved back on there if it is dirty.
    */
    list_move(&inode->i_lru, &freeable);
    percpu_counter_dec(&nr_inodes_unused);
    @@ -712,7 +709,6 @@ static void prune_icache(int nr_to_scan)
    else
    __count_vm_events(PGINODESTEAL, reap);
    spin_unlock(&inode_lru_lock);
    - spin_unlock(&inode_lock);

    dispose_list(&freeable);
    up_read(&iprune_sem);
    @@ -1429,7 +1425,6 @@ static void iput_final(struct inode *inode)
    const struct super_operations *op = inode->i_sb->s_op;
    int drop;

    - spin_lock(&inode->i_lock);
    WARN_ON(inode->i_state & I_NEW);

    if (op && op->drop_inode)
    @@ -1442,16 +1437,13 @@ static void iput_final(struct inode *inode)
    if (!(inode->i_state & (I_DIRTY|I_SYNC)))
    inode_lru_list_add(inode);
    spin_unlock(&inode->i_lock);
    - spin_unlock(&inode_lock);
    return;
    }

    if (!drop) {
    inode->i_state |= I_WILL_FREE;
    spin_unlock(&inode->i_lock);
    - spin_unlock(&inode_lock);
    write_inode_now(inode, 1);
    - spin_lock(&inode_lock);
    spin_lock(&inode->i_lock);
    WARN_ON(inode->i_state & I_NEW);
    inode->i_state &= ~I_WILL_FREE;
    @@ -1460,7 +1452,6 @@ static void iput_final(struct inode *inode)
    inode->i_state |= I_FREEING;
    inode_lru_list_del(inode);
    spin_unlock(&inode->i_lock);
    - spin_unlock(&inode_lock);

    dispose_one_inode(inode);
    }
    @@ -1479,7 +1470,7 @@ void iput(struct inode *inode)
    if (inode) {
    BUG_ON(inode->i_state & I_CLEAR);

    - if (atomic_dec_and_lock(&inode->i_count, &inode_lock))
    + if (atomic_dec_and_lock(&inode->i_count, &inode->i_lock))
    iput_final(inode);
    }
    }
    --
    1.7.1
    --
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