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       1                 :            : /* SPDX-License-Identifier: GPL-2.0 */
       2                 :            : #ifndef IOCONTEXT_H
       3                 :            : #define IOCONTEXT_H
       4                 :            : 
       5                 :            : #include <linux/radix-tree.h>
       6                 :            : #include <linux/rcupdate.h>
       7                 :            : #include <linux/workqueue.h>
       8                 :            : 
       9                 :            : enum {
      10                 :            :         ICQ_EXITED              = 1 << 2,
      11                 :            :         ICQ_DESTROYED           = 1 << 3,
      12                 :            : };
      13                 :            : 
      14                 :            : /*
      15                 :            :  * An io_cq (icq) is association between an io_context (ioc) and a
      16                 :            :  * request_queue (q).  This is used by elevators which need to track
      17                 :            :  * information per ioc - q pair.
      18                 :            :  *
      19                 :            :  * Elevator can request use of icq by setting elevator_type->icq_size and
      20                 :            :  * ->icq_align.  Both size and align must be larger than that of struct
      21                 :            :  * io_cq and elevator can use the tail area for private information.  The
      22                 :            :  * recommended way to do this is defining a struct which contains io_cq as
      23                 :            :  * the first member followed by private members and using its size and
      24                 :            :  * align.  For example,
      25                 :            :  *
      26                 :            :  *      struct snail_io_cq {
      27                 :            :  *              struct io_cq    icq;
      28                 :            :  *              int             poke_snail;
      29                 :            :  *              int             feed_snail;
      30                 :            :  *      };
      31                 :            :  *
      32                 :            :  *      struct elevator_type snail_elv_type {
      33                 :            :  *              .ops =          { ... },
      34                 :            :  *              .icq_size =     sizeof(struct snail_io_cq),
      35                 :            :  *              .icq_align =    __alignof__(struct snail_io_cq),
      36                 :            :  *              ...
      37                 :            :  *      };
      38                 :            :  *
      39                 :            :  * If icq_size is set, block core will manage icq's.  All requests will
      40                 :            :  * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
      41                 :            :  * is called and be holding a reference to the associated io_context.
      42                 :            :  *
      43                 :            :  * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
      44                 :            :  * called and, on destruction, ->elevator_exit_icq_fn().  Both functions
      45                 :            :  * are called with both the associated io_context and queue locks held.
      46                 :            :  *
      47                 :            :  * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
      48                 :            :  * queue lock but the returned icq is valid only until the queue lock is
      49                 :            :  * released.  Elevators can not and should not try to create or destroy
      50                 :            :  * icq's.
      51                 :            :  *
      52                 :            :  * As icq's are linked from both ioc and q, the locking rules are a bit
      53                 :            :  * complex.
      54                 :            :  *
      55                 :            :  * - ioc lock nests inside q lock.
      56                 :            :  *
      57                 :            :  * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
      58                 :            :  *   q->icq_list and icq->q_node by q lock.
      59                 :            :  *
      60                 :            :  * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
      61                 :            :  *   itself is protected by q lock.  However, both the indexes and icq
      62                 :            :  *   itself are also RCU managed and lookup can be performed holding only
      63                 :            :  *   the q lock.
      64                 :            :  *
      65                 :            :  * - icq's are not reference counted.  They are destroyed when either the
      66                 :            :  *   ioc or q goes away.  Each request with icq set holds an extra
      67                 :            :  *   reference to ioc to ensure it stays until the request is completed.
      68                 :            :  *
      69                 :            :  * - Linking and unlinking icq's are performed while holding both ioc and q
      70                 :            :  *   locks.  Due to the lock ordering, q exit is simple but ioc exit
      71                 :            :  *   requires reverse-order double lock dance.
      72                 :            :  */
      73                 :            : struct io_cq {
      74                 :            :         struct request_queue    *q;
      75                 :            :         struct io_context       *ioc;
      76                 :            : 
      77                 :            :         /*
      78                 :            :          * q_node and ioc_node link io_cq through icq_list of q and ioc
      79                 :            :          * respectively.  Both fields are unused once ioc_exit_icq() is
      80                 :            :          * called and shared with __rcu_icq_cache and __rcu_head which are
      81                 :            :          * used for RCU free of io_cq.
      82                 :            :          */
      83                 :            :         union {
      84                 :            :                 struct list_head        q_node;
      85                 :            :                 struct kmem_cache       *__rcu_icq_cache;
      86                 :            :         };
      87                 :            :         union {
      88                 :            :                 struct hlist_node       ioc_node;
      89                 :            :                 struct rcu_head         __rcu_head;
      90                 :            :         };
      91                 :            : 
      92                 :            :         unsigned int            flags;
      93                 :            : };
      94                 :            : 
      95                 :            : /*
      96                 :            :  * I/O subsystem state of the associated processes.  It is refcounted
      97                 :            :  * and kmalloc'ed. These could be shared between processes.
      98                 :            :  */
      99                 :            : struct io_context {
     100                 :            :         atomic_long_t refcount;
     101                 :            :         atomic_t active_ref;
     102                 :            :         atomic_t nr_tasks;
     103                 :            : 
     104                 :            :         /* all the fields below are protected by this lock */
     105                 :            :         spinlock_t lock;
     106                 :            : 
     107                 :            :         unsigned short ioprio;
     108                 :            : 
     109                 :            :         /*
     110                 :            :          * For request batching
     111                 :            :          */
     112                 :            :         int nr_batch_requests;     /* Number of requests left in the batch */
     113                 :            :         unsigned long last_waited; /* Time last woken after wait for request */
     114                 :            : 
     115                 :            :         struct radix_tree_root  icq_tree;
     116                 :            :         struct io_cq __rcu      *icq_hint;
     117                 :            :         struct hlist_head       icq_list;
     118                 :            : 
     119                 :            :         struct work_struct release_work;
     120                 :            : };
     121                 :            : 
     122                 :            : /**
     123                 :            :  * get_io_context_active - get active reference on ioc
     124                 :            :  * @ioc: ioc of interest
     125                 :            :  *
     126                 :            :  * Only iocs with active reference can issue new IOs.  This function
     127                 :            :  * acquires an active reference on @ioc.  The caller must already have an
     128                 :            :  * active reference on @ioc.
     129                 :            :  */
     130                 :          0 : static inline void get_io_context_active(struct io_context *ioc)
     131                 :            : {
     132   [ #  #  #  # ]:          0 :         WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
     133   [ #  #  #  # ]:          0 :         WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
     134                 :          0 :         atomic_long_inc(&ioc->refcount);
     135                 :          0 :         atomic_inc(&ioc->active_ref);
     136                 :          0 : }
     137                 :            : 
     138                 :          0 : static inline void ioc_task_link(struct io_context *ioc)
     139                 :            : {
     140                 :          0 :         get_io_context_active(ioc);
     141                 :            : 
     142   [ #  #  #  # ]:          0 :         WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
     143                 :          0 :         atomic_inc(&ioc->nr_tasks);
     144                 :          0 : }
     145                 :            : 
     146                 :            : struct task_struct;
     147                 :            : #ifdef CONFIG_BLOCK
     148                 :            : void put_io_context(struct io_context *ioc);
     149                 :            : void put_io_context_active(struct io_context *ioc);
     150                 :            : void exit_io_context(struct task_struct *task);
     151                 :            : struct io_context *get_task_io_context(struct task_struct *task,
     152                 :            :                                        gfp_t gfp_flags, int node);
     153                 :            : #else
     154                 :            : struct io_context;
     155                 :            : static inline void put_io_context(struct io_context *ioc) { }
     156                 :            : static inline void exit_io_context(struct task_struct *task) { }
     157                 :            : #endif
     158                 :            : 
     159                 :            : #endif