• Gerd Rausch's avatar
    net/rds: Get rid of "wait_clean_list_grace" and add locking · c9467447
    Gerd Rausch authored
    Waiting for activity on the "clean_list" to quiesce is no substitute
    for proper locking.
    
    We can have multiple threads competing for "llist_del_first"
    via "rds_ib_reuse_mr", and a single thread competing
    for "llist_del_all" and "llist_del_first" via "rds_ib_flush_mr_pool".
    
    Since "llist_del_first" depends on "list->first->next" not to change
    in the midst of the operation, simply waiting for all current calls
    to "rds_ib_reuse_mr" to quiesce across all CPUs is woefully inadequate:
    
    By the time "wait_clean_list_grace" is done iterating over all CPUs to see
    that there is no concurrent caller to "rds_ib_reuse_mr", a new caller may
    have just shown up on the first CPU.
    
    Furthermore, <linux/llist.h> explicitly calls out the need for locking:
     * Cases where locking is needed:
     * If we have multiple consumers with llist_del_first used in one consumer,
     * and llist_del_first or llist_del_all used in other consumers,
     * then a lock is needed.
    
    Also, while at it, drop the unused "pool" parameter
    from "list_to_llist_nodes".
    Signed-off-by: default avatarGerd Rausch <gerd.rausch@oracle.com>
    Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@oracle.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    c9467447
ib_rdma.c 16 KB