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       1                 :            : /* SPDX-License-Identifier: GPL-2.0 */
       2                 :            : #ifndef __LINUX_SEQLOCK_H
       3                 :            : #define __LINUX_SEQLOCK_H
       4                 :            : /*
       5                 :            :  * Reader/writer consistent mechanism without starving writers. This type of
       6                 :            :  * lock for data where the reader wants a consistent set of information
       7                 :            :  * and is willing to retry if the information changes. There are two types
       8                 :            :  * of readers:
       9                 :            :  * 1. Sequence readers which never block a writer but they may have to retry
      10                 :            :  *    if a writer is in progress by detecting change in sequence number.
      11                 :            :  *    Writers do not wait for a sequence reader.
      12                 :            :  * 2. Locking readers which will wait if a writer or another locking reader
      13                 :            :  *    is in progress. A locking reader in progress will also block a writer
      14                 :            :  *    from going forward. Unlike the regular rwlock, the read lock here is
      15                 :            :  *    exclusive so that only one locking reader can get it.
      16                 :            :  *
      17                 :            :  * This is not as cache friendly as brlock. Also, this may not work well
      18                 :            :  * for data that contains pointers, because any writer could
      19                 :            :  * invalidate a pointer that a reader was following.
      20                 :            :  *
      21                 :            :  * Expected non-blocking reader usage:
      22                 :            :  *      do {
      23                 :            :  *          seq = read_seqbegin(&foo);
      24                 :            :  *      ...
      25                 :            :  *      } while (read_seqretry(&foo, seq));
      26                 :            :  *
      27                 :            :  *
      28                 :            :  * On non-SMP the spin locks disappear but the writer still needs
      29                 :            :  * to increment the sequence variables because an interrupt routine could
      30                 :            :  * change the state of the data.
      31                 :            :  *
      32                 :            :  * Based on x86_64 vsyscall gettimeofday 
      33                 :            :  * by Keith Owens and Andrea Arcangeli
      34                 :            :  */
      35                 :            : 
      36                 :            : #include <linux/spinlock.h>
      37                 :            : #include <linux/preempt.h>
      38                 :            : #include <linux/lockdep.h>
      39                 :            : #include <linux/compiler.h>
      40                 :            : #include <asm/processor.h>
      41                 :            : 
      42                 :            : /*
      43                 :            :  * Version using sequence counter only.
      44                 :            :  * This can be used when code has its own mutex protecting the
      45                 :            :  * updating starting before the write_seqcountbeqin() and ending
      46                 :            :  * after the write_seqcount_end().
      47                 :            :  */
      48                 :            : typedef struct seqcount {
      49                 :            :         unsigned sequence;
      50                 :            : #ifdef CONFIG_DEBUG_LOCK_ALLOC
      51                 :            :         struct lockdep_map dep_map;
      52                 :            : #endif
      53                 :            : } seqcount_t;
      54                 :            : 
      55                 :            : static inline void __seqcount_init(seqcount_t *s, const char *name,
      56                 :            :                                           struct lock_class_key *key)
      57                 :            : {
      58                 :            :         /*
      59                 :            :          * Make sure we are not reinitializing a held lock:
      60                 :            :          */
      61                 :            :         lockdep_init_map(&s->dep_map, name, key, 0);
      62                 :          3 :         s->sequence = 0;
      63                 :            : }
      64                 :            : 
      65                 :            : #ifdef CONFIG_DEBUG_LOCK_ALLOC
      66                 :            : # define SEQCOUNT_DEP_MAP_INIT(lockname) \
      67                 :            :                 .dep_map = { .name = #lockname } \
      68                 :            : 
      69                 :            : # define seqcount_init(s)                               \
      70                 :            :         do {                                            \
      71                 :            :                 static struct lock_class_key __key;     \
      72                 :            :                 __seqcount_init((s), #s, &__key);   \
      73                 :            :         } while (0)
      74                 :            : 
      75                 :            : static inline void seqcount_lockdep_reader_access(const seqcount_t *s)
      76                 :            : {
      77                 :            :         seqcount_t *l = (seqcount_t *)s;
      78                 :            :         unsigned long flags;
      79                 :            : 
      80                 :            :         local_irq_save(flags);
      81                 :            :         seqcount_acquire_read(&l->dep_map, 0, 0, _RET_IP_);
      82                 :            :         seqcount_release(&l->dep_map, 1, _RET_IP_);
      83                 :            :         local_irq_restore(flags);
      84                 :            : }
      85                 :            : 
      86                 :            : #else
      87                 :            : # define SEQCOUNT_DEP_MAP_INIT(lockname)
      88                 :            : # define seqcount_init(s) __seqcount_init(s, NULL, NULL)
      89                 :            : # define seqcount_lockdep_reader_access(x)
      90                 :            : #endif
      91                 :            : 
      92                 :            : #define SEQCNT_ZERO(lockname) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(lockname)}
      93                 :            : 
      94                 :            : 
      95                 :            : /**
      96                 :            :  * __read_seqcount_begin - begin a seq-read critical section (without barrier)
      97                 :            :  * @s: pointer to seqcount_t
      98                 :            :  * Returns: count to be passed to read_seqcount_retry
      99                 :            :  *
     100                 :            :  * __read_seqcount_begin is like read_seqcount_begin, but has no smp_rmb()
     101                 :            :  * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
     102                 :            :  * provided before actually loading any of the variables that are to be
     103                 :            :  * protected in this critical section.
     104                 :            :  *
     105                 :            :  * Use carefully, only in critical code, and comment how the barrier is
     106                 :            :  * provided.
     107                 :            :  */
     108                 :            : static inline unsigned __read_seqcount_begin(const seqcount_t *s)
     109                 :            : {
     110                 :            :         unsigned ret;
     111                 :            : 
     112                 :            : repeat:
     113                 :            :         ret = READ_ONCE(s->sequence);
     114                 :          3 :         if (unlikely(ret & 1)) {
     115                 :          3 :                 cpu_relax();
     116                 :            :                 goto repeat;
     117                 :            :         }
     118                 :          3 :         return ret;
     119                 :            : }
     120                 :            : 
     121                 :            : /**
     122                 :            :  * raw_read_seqcount - Read the raw seqcount
     123                 :            :  * @s: pointer to seqcount_t
     124                 :            :  * Returns: count to be passed to read_seqcount_retry
     125                 :            :  *
     126                 :            :  * raw_read_seqcount opens a read critical section of the given
     127                 :            :  * seqcount without any lockdep checking and without checking or
     128                 :            :  * masking the LSB. Calling code is responsible for handling that.
     129                 :            :  */
     130                 :            : static inline unsigned raw_read_seqcount(const seqcount_t *s)
     131                 :            : {
     132                 :            :         unsigned ret = READ_ONCE(s->sequence);
     133                 :          3 :         smp_rmb();
     134                 :            :         return ret;
     135                 :            : }
     136                 :            : 
     137                 :            : /**
     138                 :            :  * raw_read_seqcount_begin - start seq-read critical section w/o lockdep
     139                 :            :  * @s: pointer to seqcount_t
     140                 :            :  * Returns: count to be passed to read_seqcount_retry
     141                 :            :  *
     142                 :            :  * raw_read_seqcount_begin opens a read critical section of the given
     143                 :            :  * seqcount, but without any lockdep checking. Validity of the critical
     144                 :            :  * section is tested by checking read_seqcount_retry function.
     145                 :            :  */
     146                 :            : static inline unsigned raw_read_seqcount_begin(const seqcount_t *s)
     147                 :            : {
     148                 :            :         unsigned ret = __read_seqcount_begin(s);
     149                 :          3 :         smp_rmb();
     150                 :            :         return ret;
     151                 :            : }
     152                 :            : 
     153                 :            : /**
     154                 :            :  * read_seqcount_begin - begin a seq-read critical section
     155                 :            :  * @s: pointer to seqcount_t
     156                 :            :  * Returns: count to be passed to read_seqcount_retry
     157                 :            :  *
     158                 :            :  * read_seqcount_begin opens a read critical section of the given seqcount.
     159                 :            :  * Validity of the critical section is tested by checking read_seqcount_retry
     160                 :            :  * function.
     161                 :            :  */
     162                 :            : static inline unsigned read_seqcount_begin(const seqcount_t *s)
     163                 :            : {
     164                 :            :         seqcount_lockdep_reader_access(s);
     165                 :            :         return raw_read_seqcount_begin(s);
     166                 :            : }
     167                 :            : 
     168                 :            : /**
     169                 :            :  * raw_seqcount_begin - begin a seq-read critical section
     170                 :            :  * @s: pointer to seqcount_t
     171                 :            :  * Returns: count to be passed to read_seqcount_retry
     172                 :            :  *
     173                 :            :  * raw_seqcount_begin opens a read critical section of the given seqcount.
     174                 :            :  * Validity of the critical section is tested by checking read_seqcount_retry
     175                 :            :  * function.
     176                 :            :  *
     177                 :            :  * Unlike read_seqcount_begin(), this function will not wait for the count
     178                 :            :  * to stabilize. If a writer is active when we begin, we will fail the
     179                 :            :  * read_seqcount_retry() instead of stabilizing at the beginning of the
     180                 :            :  * critical section.
     181                 :            :  */
     182                 :            : static inline unsigned raw_seqcount_begin(const seqcount_t *s)
     183                 :            : {
     184                 :            :         unsigned ret = READ_ONCE(s->sequence);
     185                 :          3 :         smp_rmb();
     186                 :          3 :         return ret & ~1;
     187                 :            : }
     188                 :            : 
     189                 :            : /**
     190                 :            :  * __read_seqcount_retry - end a seq-read critical section (without barrier)
     191                 :            :  * @s: pointer to seqcount_t
     192                 :            :  * @start: count, from read_seqcount_begin
     193                 :            :  * Returns: 1 if retry is required, else 0
     194                 :            :  *
     195                 :            :  * __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb()
     196                 :            :  * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
     197                 :            :  * provided before actually loading any of the variables that are to be
     198                 :            :  * protected in this critical section.
     199                 :            :  *
     200                 :            :  * Use carefully, only in critical code, and comment how the barrier is
     201                 :            :  * provided.
     202                 :            :  */
     203                 :            : static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start)
     204                 :            : {
     205                 :          3 :         return unlikely(s->sequence != start);
     206                 :            : }
     207                 :            : 
     208                 :            : /**
     209                 :            :  * read_seqcount_retry - end a seq-read critical section
     210                 :            :  * @s: pointer to seqcount_t
     211                 :            :  * @start: count, from read_seqcount_begin
     212                 :            :  * Returns: 1 if retry is required, else 0
     213                 :            :  *
     214                 :            :  * read_seqcount_retry closes a read critical section of the given seqcount.
     215                 :            :  * If the critical section was invalid, it must be ignored (and typically
     216                 :            :  * retried).
     217                 :            :  */
     218                 :          3 : static inline int read_seqcount_retry(const seqcount_t *s, unsigned start)
     219                 :            : {
     220                 :          3 :         smp_rmb();
     221                 :          3 :         return __read_seqcount_retry(s, start);
     222                 :            : }
     223                 :            : 
     224                 :            : 
     225                 :            : 
     226                 :            : static inline void raw_write_seqcount_begin(seqcount_t *s)
     227                 :            : {
     228                 :          3 :         s->sequence++;
     229                 :          3 :         smp_wmb();
     230                 :            : }
     231                 :            : 
     232                 :            : static inline void raw_write_seqcount_end(seqcount_t *s)
     233                 :            : {
     234                 :          3 :         smp_wmb();
     235                 :          3 :         s->sequence++;
     236                 :            : }
     237                 :            : 
     238                 :            : /**
     239                 :            :  * raw_write_seqcount_barrier - do a seq write barrier
     240                 :            :  * @s: pointer to seqcount_t
     241                 :            :  *
     242                 :            :  * This can be used to provide an ordering guarantee instead of the
     243                 :            :  * usual consistency guarantee. It is one wmb cheaper, because we can
     244                 :            :  * collapse the two back-to-back wmb()s.
     245                 :            :  *
     246                 :            :  *      seqcount_t seq;
     247                 :            :  *      bool X = true, Y = false;
     248                 :            :  *
     249                 :            :  *      void read(void)
     250                 :            :  *      {
     251                 :            :  *              bool x, y;
     252                 :            :  *
     253                 :            :  *              do {
     254                 :            :  *                      int s = read_seqcount_begin(&seq);
     255                 :            :  *
     256                 :            :  *                      x = X; y = Y;
     257                 :            :  *
     258                 :            :  *              } while (read_seqcount_retry(&seq, s));
     259                 :            :  *
     260                 :            :  *              BUG_ON(!x && !y);
     261                 :            :  *      }
     262                 :            :  *
     263                 :            :  *      void write(void)
     264                 :            :  *      {
     265                 :            :  *              Y = true;
     266                 :            :  *
     267                 :            :  *              raw_write_seqcount_barrier(seq);
     268                 :            :  *
     269                 :            :  *              X = false;
     270                 :            :  *      }
     271                 :            :  */
     272                 :            : static inline void raw_write_seqcount_barrier(seqcount_t *s)
     273                 :            : {
     274                 :          3 :         s->sequence++;
     275                 :          3 :         smp_wmb();
     276                 :          3 :         s->sequence++;
     277                 :            : }
     278                 :            : 
     279                 :          3 : static inline int raw_read_seqcount_latch(seqcount_t *s)
     280                 :            : {
     281                 :            :         /* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */
     282                 :          3 :         int seq = READ_ONCE(s->sequence); /* ^^^ */
     283                 :          3 :         return seq;
     284                 :            : }
     285                 :            : 
     286                 :            : /**
     287                 :            :  * raw_write_seqcount_latch - redirect readers to even/odd copy
     288                 :            :  * @s: pointer to seqcount_t
     289                 :            :  *
     290                 :            :  * The latch technique is a multiversion concurrency control method that allows
     291                 :            :  * queries during non-atomic modifications. If you can guarantee queries never
     292                 :            :  * interrupt the modification -- e.g. the concurrency is strictly between CPUs
     293                 :            :  * -- you most likely do not need this.
     294                 :            :  *
     295                 :            :  * Where the traditional RCU/lockless data structures rely on atomic
     296                 :            :  * modifications to ensure queries observe either the old or the new state the
     297                 :            :  * latch allows the same for non-atomic updates. The trade-off is doubling the
     298                 :            :  * cost of storage; we have to maintain two copies of the entire data
     299                 :            :  * structure.
     300                 :            :  *
     301                 :            :  * Very simply put: we first modify one copy and then the other. This ensures
     302                 :            :  * there is always one copy in a stable state, ready to give us an answer.
     303                 :            :  *
     304                 :            :  * The basic form is a data structure like:
     305                 :            :  *
     306                 :            :  * struct latch_struct {
     307                 :            :  *      seqcount_t              seq;
     308                 :            :  *      struct data_struct      data[2];
     309                 :            :  * };
     310                 :            :  *
     311                 :            :  * Where a modification, which is assumed to be externally serialized, does the
     312                 :            :  * following:
     313                 :            :  *
     314                 :            :  * void latch_modify(struct latch_struct *latch, ...)
     315                 :            :  * {
     316                 :            :  *      smp_wmb();      <- Ensure that the last data[1] update is visible
     317                 :            :  *      latch->seq++;
     318                 :            :  *      smp_wmb();      <- Ensure that the seqcount update is visible
     319                 :            :  *
     320                 :            :  *      modify(latch->data[0], ...);
     321                 :            :  *
     322                 :            :  *      smp_wmb();      <- Ensure that the data[0] update is visible
     323                 :            :  *      latch->seq++;
     324                 :            :  *      smp_wmb();      <- Ensure that the seqcount update is visible
     325                 :            :  *
     326                 :            :  *      modify(latch->data[1], ...);
     327                 :            :  * }
     328                 :            :  *
     329                 :            :  * The query will have a form like:
     330                 :            :  *
     331                 :            :  * struct entry *latch_query(struct latch_struct *latch, ...)
     332                 :            :  * {
     333                 :            :  *      struct entry *entry;
     334                 :            :  *      unsigned seq, idx;
     335                 :            :  *
     336                 :            :  *      do {
     337                 :            :  *              seq = raw_read_seqcount_latch(&latch->seq);
     338                 :            :  *
     339                 :            :  *              idx = seq & 0x01;
     340                 :            :  *              entry = data_query(latch->data[idx], ...);
     341                 :            :  *
     342                 :            :  *              smp_rmb();
     343                 :            :  *      } while (seq != latch->seq);
     344                 :            :  *
     345                 :            :  *      return entry;
     346                 :            :  * }
     347                 :            :  *
     348                 :            :  * So during the modification, queries are first redirected to data[1]. Then we
     349                 :            :  * modify data[0]. When that is complete, we redirect queries back to data[0]
     350                 :            :  * and we can modify data[1].
     351                 :            :  *
     352                 :            :  * NOTE: The non-requirement for atomic modifications does _NOT_ include
     353                 :            :  *       the publishing of new entries in the case where data is a dynamic
     354                 :            :  *       data structure.
     355                 :            :  *
     356                 :            :  *       An iteration might start in data[0] and get suspended long enough
     357                 :            :  *       to miss an entire modification sequence, once it resumes it might
     358                 :            :  *       observe the new entry.
     359                 :            :  *
     360                 :            :  * NOTE: When data is a dynamic data structure; one should use regular RCU
     361                 :            :  *       patterns to manage the lifetimes of the objects within.
     362                 :            :  */
     363                 :          3 : static inline void raw_write_seqcount_latch(seqcount_t *s)
     364                 :            : {
     365                 :          3 :        smp_wmb();      /* prior stores before incrementing "sequence" */
     366                 :          3 :        s->sequence++;
     367                 :          3 :        smp_wmb();      /* increment "sequence" before following stores */
     368                 :          3 : }
     369                 :            : 
     370                 :            : /*
     371                 :            :  * Sequence counter only version assumes that callers are using their
     372                 :            :  * own mutexing.
     373                 :            :  */
     374                 :            : static inline void write_seqcount_begin_nested(seqcount_t *s, int subclass)
     375                 :            : {
     376                 :            :         raw_write_seqcount_begin(s);
     377                 :            :         seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
     378                 :            : }
     379                 :            : 
     380                 :            : static inline void write_seqcount_begin(seqcount_t *s)
     381                 :            : {
     382                 :            :         write_seqcount_begin_nested(s, 0);
     383                 :            : }
     384                 :            : 
     385                 :            : static inline void write_seqcount_end(seqcount_t *s)
     386                 :            : {
     387                 :            :         seqcount_release(&s->dep_map, 1, _RET_IP_);
     388                 :            :         raw_write_seqcount_end(s);
     389                 :            : }
     390                 :            : 
     391                 :            : /**
     392                 :            :  * write_seqcount_invalidate - invalidate in-progress read-side seq operations
     393                 :            :  * @s: pointer to seqcount_t
     394                 :            :  *
     395                 :            :  * After write_seqcount_invalidate, no read-side seq operations will complete
     396                 :            :  * successfully and see data older than this.
     397                 :            :  */
     398                 :            : static inline void write_seqcount_invalidate(seqcount_t *s)
     399                 :            : {
     400                 :          3 :         smp_wmb();
     401                 :          3 :         s->sequence+=2;
     402                 :            : }
     403                 :            : 
     404                 :            : typedef struct {
     405                 :            :         struct seqcount seqcount;
     406                 :            :         spinlock_t lock;
     407                 :            : } seqlock_t;
     408                 :            : 
     409                 :            : /*
     410                 :            :  * These macros triggered gcc-3.x compile-time problems.  We think these are
     411                 :            :  * OK now.  Be cautious.
     412                 :            :  */
     413                 :            : #define __SEQLOCK_UNLOCKED(lockname)                    \
     414                 :            :         {                                               \
     415                 :            :                 .seqcount = SEQCNT_ZERO(lockname),      \
     416                 :            :                 .lock = __SPIN_LOCK_UNLOCKED(lockname)  \
     417                 :            :         }
     418                 :            : 
     419                 :            : #define seqlock_init(x)                                 \
     420                 :            :         do {                                            \
     421                 :            :                 seqcount_init(&(x)->seqcount);           \
     422                 :            :                 spin_lock_init(&(x)->lock);              \
     423                 :            :         } while (0)
     424                 :            : 
     425                 :            : #define DEFINE_SEQLOCK(x) \
     426                 :            :                 seqlock_t x = __SEQLOCK_UNLOCKED(x)
     427                 :            : 
     428                 :            : /*
     429                 :            :  * Read side functions for starting and finalizing a read side section.
     430                 :            :  */
     431                 :            : static inline unsigned read_seqbegin(const seqlock_t *sl)
     432                 :            : {
     433                 :            :         return read_seqcount_begin(&sl->seqcount);
     434                 :            : }
     435                 :            : 
     436                 :            : static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
     437                 :            : {
     438                 :            :         return read_seqcount_retry(&sl->seqcount, start);
     439                 :            : }
     440                 :            : 
     441                 :            : /*
     442                 :            :  * Lock out other writers and update the count.
     443                 :            :  * Acts like a normal spin_lock/unlock.
     444                 :            :  * Don't need preempt_disable() because that is in the spin_lock already.
     445                 :            :  */
     446                 :            : static inline void write_seqlock(seqlock_t *sl)
     447                 :            : {
     448                 :            :         spin_lock(&sl->lock);
     449                 :            :         write_seqcount_begin(&sl->seqcount);
     450                 :            : }
     451                 :            : 
     452                 :            : static inline void write_sequnlock(seqlock_t *sl)
     453                 :            : {
     454                 :            :         write_seqcount_end(&sl->seqcount);
     455                 :            :         spin_unlock(&sl->lock);
     456                 :            : }
     457                 :            : 
     458                 :            : static inline void write_seqlock_bh(seqlock_t *sl)
     459                 :            : {
     460                 :            :         spin_lock_bh(&sl->lock);
     461                 :            :         write_seqcount_begin(&sl->seqcount);
     462                 :            : }
     463                 :            : 
     464                 :            : static inline void write_sequnlock_bh(seqlock_t *sl)
     465                 :            : {
     466                 :            :         write_seqcount_end(&sl->seqcount);
     467                 :            :         spin_unlock_bh(&sl->lock);
     468                 :            : }
     469                 :            : 
     470                 :            : static inline void write_seqlock_irq(seqlock_t *sl)
     471                 :            : {
     472                 :            :         spin_lock_irq(&sl->lock);
     473                 :            :         write_seqcount_begin(&sl->seqcount);
     474                 :            : }
     475                 :            : 
     476                 :            : static inline void write_sequnlock_irq(seqlock_t *sl)
     477                 :            : {
     478                 :            :         write_seqcount_end(&sl->seqcount);
     479                 :            :         spin_unlock_irq(&sl->lock);
     480                 :            : }
     481                 :            : 
     482                 :            : static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
     483                 :            : {
     484                 :            :         unsigned long flags;
     485                 :            : 
     486                 :          0 :         spin_lock_irqsave(&sl->lock, flags);
     487                 :            :         write_seqcount_begin(&sl->seqcount);
     488                 :            :         return flags;
     489                 :            : }
     490                 :            : 
     491                 :            : #define write_seqlock_irqsave(lock, flags)                              \
     492                 :            :         do { flags = __write_seqlock_irqsave(lock); } while (0)
     493                 :            : 
     494                 :            : static inline void
     495                 :            : write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
     496                 :            : {
     497                 :            :         write_seqcount_end(&sl->seqcount);
     498                 :            :         spin_unlock_irqrestore(&sl->lock, flags);
     499                 :            : }
     500                 :            : 
     501                 :            : /*
     502                 :            :  * A locking reader exclusively locks out other writers and locking readers,
     503                 :            :  * but doesn't update the sequence number. Acts like a normal spin_lock/unlock.
     504                 :            :  * Don't need preempt_disable() because that is in the spin_lock already.
     505                 :            :  */
     506                 :            : static inline void read_seqlock_excl(seqlock_t *sl)
     507                 :            : {
     508                 :            :         spin_lock(&sl->lock);
     509                 :            : }
     510                 :            : 
     511                 :            : static inline void read_sequnlock_excl(seqlock_t *sl)
     512                 :            : {
     513                 :            :         spin_unlock(&sl->lock);
     514                 :            : }
     515                 :            : 
     516                 :            : /**
     517                 :            :  * read_seqbegin_or_lock - begin a sequence number check or locking block
     518                 :            :  * @lock: sequence lock
     519                 :            :  * @seq : sequence number to be checked
     520                 :            :  *
     521                 :            :  * First try it once optimistically without taking the lock. If that fails,
     522                 :            :  * take the lock. The sequence number is also used as a marker for deciding
     523                 :            :  * whether to be a reader (even) or writer (odd).
     524                 :            :  * N.B. seq must be initialized to an even number to begin with.
     525                 :            :  */
     526                 :          3 : static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
     527                 :            : {
     528                 :          3 :         if (!(*seq & 1))    /* Even */
     529                 :          3 :                 *seq = read_seqbegin(lock);
     530                 :            :         else                    /* Odd */
     531                 :            :                 read_seqlock_excl(lock);
     532                 :          3 : }
     533                 :            : 
     534                 :            : static inline int need_seqretry(seqlock_t *lock, int seq)
     535                 :            : {
     536                 :          3 :         return !(seq & 1) && read_seqretry(lock, seq);
     537                 :            : }
     538                 :            : 
     539                 :            : static inline void done_seqretry(seqlock_t *lock, int seq)
     540                 :            : {
     541                 :          3 :         if (seq & 1)
     542                 :            :                 read_sequnlock_excl(lock);
     543                 :            : }
     544                 :            : 
     545                 :            : static inline void read_seqlock_excl_bh(seqlock_t *sl)
     546                 :            : {
     547                 :            :         spin_lock_bh(&sl->lock);
     548                 :            : }
     549                 :            : 
     550                 :            : static inline void read_sequnlock_excl_bh(seqlock_t *sl)
     551                 :            : {
     552                 :            :         spin_unlock_bh(&sl->lock);
     553                 :            : }
     554                 :            : 
     555                 :            : static inline void read_seqlock_excl_irq(seqlock_t *sl)
     556                 :            : {
     557                 :            :         spin_lock_irq(&sl->lock);
     558                 :            : }
     559                 :            : 
     560                 :            : static inline void read_sequnlock_excl_irq(seqlock_t *sl)
     561                 :            : {
     562                 :            :         spin_unlock_irq(&sl->lock);
     563                 :            : }
     564                 :            : 
     565                 :            : static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl)
     566                 :            : {
     567                 :            :         unsigned long flags;
     568                 :            : 
     569                 :          0 :         spin_lock_irqsave(&sl->lock, flags);
     570                 :            :         return flags;
     571                 :            : }
     572                 :            : 
     573                 :            : #define read_seqlock_excl_irqsave(lock, flags)                          \
     574                 :            :         do { flags = __read_seqlock_excl_irqsave(lock); } while (0)
     575                 :            : 
     576                 :            : static inline void
     577                 :            : read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
     578                 :            : {
     579                 :            :         spin_unlock_irqrestore(&sl->lock, flags);
     580                 :            : }
     581                 :            : 
     582                 :            : static inline unsigned long
     583                 :          3 : read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
     584                 :            : {
     585                 :            :         unsigned long flags = 0;
     586                 :            : 
     587                 :          3 :         if (!(*seq & 1))    /* Even */
     588                 :          3 :                 *seq = read_seqbegin(lock);
     589                 :            :         else                    /* Odd */
     590                 :            :                 read_seqlock_excl_irqsave(lock, flags);
     591                 :            : 
     592                 :          3 :         return flags;
     593                 :            : }
     594                 :            : 
     595                 :            : static inline void
     596                 :            : done_seqretry_irqrestore(seqlock_t *lock, int seq, unsigned long flags)
     597                 :            : {
     598                 :          3 :         if (seq & 1)
     599                 :            :                 read_sequnlock_excl_irqrestore(lock, flags);
     600                 :            : }
     601                 :            : #endif /* __LINUX_SEQLOCK_H */