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 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
  * All Rights Reserved.
  */
 #ifndef __XFS_LOG_PRIV_H__
 #define __XFS_LOG_PRIV_H__
 
 struct xfs_buf;
 struct xlog;
 struct xlog_ticket;
 struct xfs_mount;
 
 /*
  * get client id from packed copy.
  *
  * this hack is here because the xlog_pack code copies four bytes
  * of xlog_op_header containing the fields oh_clientid, oh_flags
  * and oh_res2 into the packed copy.
  *
  * later on this four byte chunk is treated as an int and the
  * client id is pulled out.
  *
  * this has endian issues, of course.
  */
 static inline uint xlog_get_client_id(__be32 i)
 {
     return be32_to_cpu(i) >> 24;
 }
 
 /*
  * In core log state
  */
 enum xlog_iclog_state {
     XLOG_STATE_ACTIVE,  /* Current IC log being written to */
     XLOG_STATE_WANT_SYNC,   /* Want to sync this iclog; no more writes */
     XLOG_STATE_SYNCING, /* This IC log is syncing */
     XLOG_STATE_DONE_SYNC,   /* Done syncing to disk */
     XLOG_STATE_CALLBACK,    /* Callback functions now */
     XLOG_STATE_DIRTY,   /* Dirty IC log, not ready for ACTIVE status */
 };
 
 #define XLOG_STATE_STRINGS \
     { XLOG_STATE_ACTIVE,    "XLOG_STATE_ACTIVE" }, \
     { XLOG_STATE_WANT_SYNC, "XLOG_STATE_WANT_SYNC" }, \
     { XLOG_STATE_SYNCING,   "XLOG_STATE_SYNCING" }, \
     { XLOG_STATE_DONE_SYNC, "XLOG_STATE_DONE_SYNC" }, \
     { XLOG_STATE_CALLBACK,  "XLOG_STATE_CALLBACK" }, \
     { XLOG_STATE_DIRTY, "XLOG_STATE_DIRTY" }
 
 /*
  * In core log flags
  */
 #define XLOG_ICL_NEED_FLUSH (1u << 0)   /* iclog needs REQ_PREFLUSH */
 #define XLOG_ICL_NEED_FUA   (1u << 1)   /* iclog needs REQ_FUA */
 
 #define XLOG_ICL_STRINGS \
     { XLOG_ICL_NEED_FLUSH,  "XLOG_ICL_NEED_FLUSH" }, \
     { XLOG_ICL_NEED_FUA,    "XLOG_ICL_NEED_FUA" }
 
 
 /*
  * Log ticket flags
  */
 #define XLOG_TIC_PERM_RESERV    (1u << 0)   /* permanent reservation */
 
 #define XLOG_TIC_FLAGS \
     { XLOG_TIC_PERM_RESERV, "XLOG_TIC_PERM_RESERV" }
 
 /*
  * Below are states for covering allocation transactions.
  * By covering, we mean changing the h_tail_lsn in the last on-disk
  * log write such that no allocation transactions will be re-done during
  * recovery after a system crash. Recovery starts at the last on-disk
  * log write.
  *
  * These states are used to insert dummy log entries to cover
  * space allocation transactions which can undo non-transactional changes
  * after a crash. Writes to a file with space
  * already allocated do not result in any transactions. Allocations
  * might include space beyond the EOF. So if we just push the EOF a
  * little, the last transaction for the file could contain the wrong
  * size. If there is no file system activity, after an allocation
  * transaction, and the system crashes, the allocation transaction
  * will get replayed and the file will be truncated. This could
  * be hours/days/... after the allocation occurred.
  *
  * The fix for this is to do two dummy transactions when the
  * system is idle. We need two dummy transaction because the h_tail_lsn
  * in the log record header needs to point beyond the last possible
  * non-dummy transaction. The first dummy changes the h_tail_lsn to
  * the first transaction before the dummy. The second dummy causes
  * h_tail_lsn to point to the first dummy. Recovery starts at h_tail_lsn.
  *
  * These dummy transactions get committed when everything
  * is idle (after there has been some activity).
  *
  * There are 5 states used to control this.
  *
  *  IDLE -- no logging has been done on the file system or
  *      we are done covering previous transactions.
  *  NEED -- logging has occurred and we need a dummy transaction
  *      when the log becomes idle.
  *  DONE -- we were in the NEED state and have committed a dummy
  *      transaction.
  *  NEED2 -- we detected that a dummy transaction has gone to the
  *      on disk log with no other transactions.
  *  DONE2 -- we committed a dummy transaction when in the NEED2 state.
  *
  * There are two places where we switch states:
  *
  * 1.) In xfs_sync, when we detect an idle log and are in NEED or NEED2.
  *  We commit the dummy transaction and switch to DONE or DONE2,
  *  respectively. In all other states, we don't do anything.
  *
  * 2.) When we finish writing the on-disk log (xlog_state_clean_log).
  *
  *  No matter what state we are in, if this isn't the dummy
  *  transaction going out, the next state is NEED.
  *  So, if we aren't in the DONE or DONE2 states, the next state
  *  is NEED. We can't be finishing a write of the dummy record
  *  unless it was committed and the state switched to DONE or DONE2.
  *
  *  If we are in the DONE state and this was a write of the
  *      dummy transaction, we move to NEED2.
  *
  *  If we are in the DONE2 state and this was a write of the
  *      dummy transaction, we move to IDLE.
  *
  *
  * Writing only one dummy transaction can get appended to
  * one file space allocation. When this happens, the log recovery
  * code replays the space allocation and a file could be truncated.
  * This is why we have the NEED2 and DONE2 states before going idle.
  */
 
 #define XLOG_STATE_COVER_IDLE   0
 #define XLOG_STATE_COVER_NEED   1
 #define XLOG_STATE_COVER_DONE   2
 #define XLOG_STATE_COVER_NEED2  3
 #define XLOG_STATE_COVER_DONE2  4
 
 #define XLOG_COVER_OPS      5
 
 typedef struct xlog_ticket {
     struct list_head    t_queue;    /* reserve/write queue */
     struct task_struct  *t_task;    /* task that owns this ticket */
     xlog_tid_t      t_tid;      /* transaction identifier */
     atomic_t        t_ref;      /* ticket reference count */
     int         t_curr_res; /* current reservation */
     int         t_unit_res; /* unit reservation */
     char            t_ocnt;     /* original unit count */
     char            t_cnt;      /* current unit count */
     uint8_t         t_flags;    /* properties of reservation */
     int         t_iclog_hdrs;   /* iclog hdrs in t_curr_res */
 } xlog_ticket_t;
 
 /*
  * - A log record header is 512 bytes.  There is plenty of room to grow the
  *  xlog_rec_header_t into the reserved space.
  * - ic_data follows, so a write to disk can start at the beginning of
  *  the iclog.
  * - ic_forcewait is used to implement synchronous forcing of the iclog to disk.
  * - ic_next is the pointer to the next iclog in the ring.
  * - ic_log is a pointer back to the global log structure.
  * - ic_size is the full size of the log buffer, minus the cycle headers.
  * - ic_offset is the current number of bytes written to in this iclog.
  * - ic_refcnt is bumped when someone is writing to the log.
  * - ic_state is the state of the iclog.
  *
  * Because of cacheline contention on large machines, we need to separate
  * various resources onto different cachelines. To start with, make the
  * structure cacheline aligned. The following fields can be contended on
  * by independent processes:
  *
  *  - ic_callbacks
  *  - ic_refcnt
  *  - fields protected by the global l_icloglock
  *
  * so we need to ensure that these fields are located in separate cachelines.
  * We'll put all the read-only and l_icloglock fields in the first cacheline,
  * and move everything else out to subsequent cachelines.
  */
 typedef struct xlog_in_core {
     wait_queue_head_t   ic_force_wait;
     wait_queue_head_t   ic_write_wait;
     struct xlog_in_core *ic_next;
     struct xlog_in_core *ic_prev;
     struct xlog     *ic_log;
     u32         ic_size;
     u32         ic_offset;
     enum xlog_iclog_state   ic_state;
     unsigned int        ic_flags;
     void            *ic_datap;  /* pointer to iclog data */
     struct list_head    ic_callbacks;
 
     /* reference counts need their own cacheline */
     atomic_t        ic_refcnt ____cacheline_aligned_in_smp;
     xlog_in_core_2_t    *ic_data;
 #define ic_header   ic_data->hic_header
 #ifdef DEBUG
     bool            ic_fail_crc : 1;
 #endif
     struct semaphore    ic_sema;
     struct work_struct  ic_end_io_work;
     struct bio      ic_bio;
     struct bio_vec      ic_bvec[];
 } xlog_in_core_t;
 
 /*
  * The CIL context is used to aggregate per-transaction details as well be
  * passed to the iclog for checkpoint post-commit processing.  After being
  * passed to the iclog, another context needs to be allocated for tracking the
  * next set of transactions to be aggregated into a checkpoint.
  */
 struct xfs_cil;
 
 struct xfs_cil_ctx {
     struct xfs_cil      *cil;
     xfs_csn_t       sequence;   /* chkpt sequence # */
     xfs_lsn_t       start_lsn;  /* first LSN of chkpt commit */
     xfs_lsn_t       commit_lsn; /* chkpt commit record lsn */
     struct xlog_in_core *commit_iclog;
     struct xlog_ticket  *ticket;    /* chkpt ticket */
     atomic_t        space_used; /* aggregate size of regions */
     struct list_head    busy_extents;   /* busy extents in chkpt */
     struct list_head    log_items;  /* log items in chkpt */
     struct list_head    lv_chain;   /* logvecs being pushed */
     struct list_head    iclog_entry;
     struct list_head    committing; /* ctx committing list */
     struct work_struct  discard_endio_work;
     struct work_struct  push_work;
     atomic_t        order_id;
 };
 
 /*
  * Per-cpu CIL tracking items
  */
 struct xlog_cil_pcp {
     int32_t         space_used;
     uint32_t        space_reserved;
     struct list_head    busy_extents;
     struct list_head    log_items;
 };
 
 /*
  * Committed Item List structure
  *
  * This structure is used to track log items that have been committed but not
  * yet written into the log. It is used only when the delayed logging mount
  * option is enabled.
  *
  * This structure tracks the list of committing checkpoint contexts so
  * we can avoid the problem of having to hold out new transactions during a
  * flush until we have a the commit record LSN of the checkpoint. We can
  * traverse the list of committing contexts in xlog_cil_push_lsn() to find a
  * sequence match and extract the commit LSN directly from there. If the
  * checkpoint is still in the process of committing, we can block waiting for
  * the commit LSN to be determined as well. This should make synchronous
  * operations almost as efficient as the old logging methods.
  */
 struct xfs_cil {
     struct xlog     *xc_log;
     unsigned long       xc_flags;
     atomic_t        xc_iclog_hdrs;
     struct workqueue_struct *xc_push_wq;
 
     struct rw_semaphore xc_ctx_lock ____cacheline_aligned_in_smp;
     struct xfs_cil_ctx  *xc_ctx;
 
     spinlock_t      xc_push_lock ____cacheline_aligned_in_smp;
     xfs_csn_t       xc_push_seq;
     bool            xc_push_commit_stable;
     struct list_head    xc_committing;
     wait_queue_head_t   xc_commit_wait;
     wait_queue_head_t   xc_start_wait;
     xfs_csn_t       xc_current_sequence;
     wait_queue_head_t   xc_push_wait;   /* background push throttle */
 
     void __percpu       *xc_pcp;    /* percpu CIL structures */
 #ifdef CONFIG_HOTPLUG_CPU
     struct list_head    xc_pcp_list;
 #endif
 } ____cacheline_aligned_in_smp;
 
 /* xc_flags bit values */
 #define XLOG_CIL_EMPTY      1
 #define XLOG_CIL_PCP_SPACE  2
 
 /*
  * The amount of log space we allow the CIL to aggregate is difficult to size.
  * Whatever we choose, we have to make sure we can get a reservation for the
  * log space effectively, that it is large enough to capture sufficient
  * relogging to reduce log buffer IO significantly, but it is not too large for
  * the log or induces too much latency when writing out through the iclogs. We
  * track both space consumed and the number of vectors in the checkpoint
  * context, so we need to decide which to use for limiting.
  *
  * Every log buffer we write out during a push needs a header reserved, which
  * is at least one sector and more for v2 logs. Hence we need a reservation of
  * at least 512 bytes per 32k of log space just for the LR headers. That means
  * 16KB of reservation per megabyte of delayed logging space we will consume,
  * plus various headers.  The number of headers will vary based on the num of
  * io vectors, so limiting on a specific number of vectors is going to result
  * in transactions of varying size. IOWs, it is more consistent to track and
  * limit space consumed in the log rather than by the number of objects being
  * logged in order to prevent checkpoint ticket overruns.
  *
  * Further, use of static reservations through the log grant mechanism is
  * problematic. It introduces a lot of complexity (e.g. reserve grant vs write
  * grant) and a significant deadlock potential because regranting write space
  * can block on log pushes. Hence if we have to regrant log space during a log
  * push, we can deadlock.
  *
  * However, we can avoid this by use of a dynamic "reservation stealing"
  * technique during transaction commit whereby unused reservation space in the
  * transaction ticket is transferred to the CIL ctx commit ticket to cover the
  * space needed by the checkpoint transaction. This means that we never need to
  * specifically reserve space for the CIL checkpoint transaction, nor do we
  * need to regrant space once the checkpoint completes. This also means the
  * checkpoint transaction ticket is specific to the checkpoint context, rather
  * than the CIL itself.
  *
  * With dynamic reservations, we can effectively make up arbitrary limits for
  * the checkpoint size so long as they don't violate any other size rules.
  * Recovery imposes a rule that no transaction exceed half the log, so we are
  * limited by that.  Furthermore, the log transaction reservation subsystem
  * tries to keep 25% of the log free, so we need to keep below that limit or we
  * risk running out of free log space to start any new transactions.
  *
  * In order to keep background CIL push efficient, we only need to ensure the
  * CIL is large enough to maintain sufficient in-memory relogging to avoid
  * repeated physical writes of frequently modified metadata. If we allow the CIL
  * to grow to a substantial fraction of the log, then we may be pinning hundreds
  * of megabytes of metadata in memory until the CIL flushes. This can cause
  * issues when we are running low on memory - pinned memory cannot be reclaimed,
  * and the CIL consumes a lot of memory. Hence we need to set an upper physical
  * size limit for the CIL that limits the maximum amount of memory pinned by the
  * CIL but does not limit performance by reducing relogging efficiency
  * significantly.
  *
  * As such, the CIL push threshold ends up being the smaller of two thresholds:
  * - a threshold large enough that it allows CIL to be pushed and progress to be
  *   made without excessive blocking of incoming transaction commits. This is
  *   defined to be 12.5% of the log space - half the 25% push threshold of the
  *   AIL.
  * - small enough that it doesn't pin excessive amounts of memory but maintains
  *   close to peak relogging efficiency. This is defined to be 16x the iclog
  *   buffer window (32MB) as measurements have shown this to be roughly the
  *   point of diminishing performance increases under highly concurrent
  *   modification workloads.
  *
  * To prevent the CIL from overflowing upper commit size bounds, we introduce a
  * new threshold at which we block committing transactions until the background
  * CIL commit commences and switches to a new context. While this is not a hard
  * limit, it forces the process committing a transaction to the CIL to block and
  * yeild the CPU, giving the CIL push work a chance to be scheduled and start
  * work. This prevents a process running lots of transactions from overfilling
  * the CIL because it is not yielding the CPU. We set the blocking limit at
  * twice the background push space threshold so we keep in line with the AIL
  * push thresholds.
  *
  * Note: this is not a -hard- limit as blocking is applied after the transaction
  * is inserted into the CIL and the push has been triggered. It is largely a
  * throttling mechanism that allows the CIL push to be scheduled and run. A hard
  * limit will be difficult to implement without introducing global serialisation
  * in the CIL commit fast path, and it's not at all clear that we actually need
  * such hard limits given the ~7 years we've run without a hard limit before
  * finding the first situation where a checkpoint size overflow actually
  * occurred. Hence the simple throttle, and an ASSERT check to tell us that
  * we've overrun the max size.
  */
 #define XLOG_CIL_SPACE_LIMIT(log)   \
     min_t(int, (log)->l_logsize >> 3, BBTOB(XLOG_TOTAL_REC_SHIFT(log)) << 4)
 
 #define XLOG_CIL_BLOCKING_SPACE_LIMIT(log)  \
     (XLOG_CIL_SPACE_LIMIT(log) * 2)
 
 /*
  * ticket grant locks, queues and accounting have their own cachlines
  * as these are quite hot and can be operated on concurrently.
  */
 struct xlog_grant_head {
     spinlock_t      lock ____cacheline_aligned_in_smp;
     struct list_head    waiters;
     atomic64_t      grant;
 };
 
 /*
  * The reservation head lsn is not made up of a cycle number and block number.
  * Instead, it uses a cycle number and byte number.  Logs don't expect to
  * overflow 31 bits worth of byte offset, so using a byte number will mean
  * that round off problems won't occur when releasing partial reservations.
  */
 struct xlog {
     /* The following fields don't need locking */
     struct xfs_mount    *l_mp;          /* mount point */
     struct xfs_ail      *l_ailp;    /* AIL log is working with */
     struct xfs_cil      *l_cilp;    /* CIL log is working with */
     struct xfs_buftarg  *l_targ;        /* buftarg of log */
     struct workqueue_struct *l_ioend_workqueue; /* for I/O completions */
     struct delayed_work l_work;     /* background flush work */
     long            l_opstate;  /* operational state */
     uint            l_quotaoffs_flag; /* XFS_DQ_*, for QUOTAOFFs */
     struct list_head    *l_buf_cancel_table;
     int         l_iclog_hsize;  /* size of iclog header */
     int         l_iclog_heads;  /* # of iclog header sectors */
     uint            l_sectBBsize;   /* sector size in BBs (2^n) */
     int         l_iclog_size;   /* size of log in bytes */
     int         l_iclog_bufs;   /* number of iclog buffers */
     xfs_daddr_t     l_logBBstart;   /* start block of log */
     int         l_logsize;      /* size of log in bytes */
     int         l_logBBsize;    /* size of log in BB chunks */
 
     /* The following block of fields are changed while holding icloglock */
     wait_queue_head_t   l_flush_wait ____cacheline_aligned_in_smp;
                         /* waiting for iclog flush */
     int         l_covered_state;/* state of "covering disk
                          * log entries" */
     xlog_in_core_t      *l_iclog;       /* head log queue   */
     spinlock_t      l_icloglock;    /* grab to change iclog state */
     int         l_curr_cycle;   /* Cycle number of log writes */
     int         l_prev_cycle;   /* Cycle number before last
                          * block increment */
     int         l_curr_block;   /* current logical log block */
     int         l_prev_block;   /* previous logical log block */
 
     /*
      * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and
      * read without needing to hold specific locks. To avoid operations
      * contending with other hot objects, place each of them on a separate
      * cacheline.
      */
     /* lsn of last LR on disk */
     atomic64_t      l_last_sync_lsn ____cacheline_aligned_in_smp;
     /* lsn of 1st LR with unflushed * buffers */
     atomic64_t      l_tail_lsn ____cacheline_aligned_in_smp;
 
     struct xlog_grant_head  l_reserve_head;
     struct xlog_grant_head  l_write_head;
 
     struct xfs_kobj     l_kobj;
 
     /* log recovery lsn tracking (for buffer submission */
     xfs_lsn_t       l_recovery_lsn;
 
     uint32_t        l_iclog_roundoff;/* padding roundoff */
 
     /* Users of log incompat features should take a read lock. */
     struct rw_semaphore l_incompat_users;
 };
 
 /*
  * Bits for operational state
  */
 #define XLOG_ACTIVE_RECOVERY    0   /* in the middle of recovery */
 #define XLOG_RECOVERY_NEEDED    1   /* log was recovered */
 #define XLOG_IO_ERROR       2   /* log hit an I/O error, and being
                    shutdown */
 #define XLOG_TAIL_WARN      3   /* log tail verify warning issued */
 
 static inline bool
 xlog_recovery_needed(struct xlog *log)
 {
     return test_bit(XLOG_RECOVERY_NEEDED, &log->l_opstate);
 }
 
 static inline bool
 xlog_in_recovery(struct xlog *log)
 {
     return test_bit(XLOG_ACTIVE_RECOVERY, &log->l_opstate);
 }
 
 static inline bool
 xlog_is_shutdown(struct xlog *log)
 {
     return test_bit(XLOG_IO_ERROR, &log->l_opstate);
 }
 
 /*
  * Wait until the xlog_force_shutdown() has marked the log as shut down
  * so xlog_is_shutdown() will always return true.
  */
 static inline void
 xlog_shutdown_wait(
     struct xlog *log)
 {
     wait_var_event(&log->l_opstate, xlog_is_shutdown(log));
 }
 
 /* common routines */
 extern int
 xlog_recover(
     struct xlog     *log);
 extern int
 xlog_recover_finish(
     struct xlog     *log);
 extern void
 xlog_recover_cancel(struct xlog *);
 
 extern __le32    xlog_cksum(struct xlog *log, struct xlog_rec_header *rhead,
                 char *dp, int size);
 
 extern struct kmem_cache *xfs_log_ticket_cache;
 struct xlog_ticket *xlog_ticket_alloc(struct xlog *log, int unit_bytes,
         int count, bool permanent);
 
 void    xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
 void    xlog_print_trans(struct xfs_trans *);
 int xlog_write(struct xlog *log, struct xfs_cil_ctx *ctx,
         struct list_head *lv_chain, struct xlog_ticket *tic,
         uint32_t len);
 void    xfs_log_ticket_ungrant(struct xlog *log, struct xlog_ticket *ticket);
 void    xfs_log_ticket_regrant(struct xlog *log, struct xlog_ticket *ticket);
 
 void xlog_state_switch_iclogs(struct xlog *log, struct xlog_in_core *iclog,
         int eventual_size);
 int xlog_state_release_iclog(struct xlog *log, struct xlog_in_core *iclog,
         struct xlog_ticket *ticket);
 
 /*
  * When we crack an atomic LSN, we sample it first so that the value will not
  * change while we are cracking it into the component values. This means we
  * will always get consistent component values to work from. This should always
  * be used to sample and crack LSNs that are stored and updated in atomic
  * variables.
  */
 static inline void
 xlog_crack_atomic_lsn(atomic64_t *lsn, uint *cycle, uint *block)
 {
     xfs_lsn_t val = atomic64_read(lsn);
 
     *cycle = CYCLE_LSN(val);
     *block = BLOCK_LSN(val);
 }
 
 /*
  * Calculate and assign a value to an atomic LSN variable from component pieces.
  */
 static inline void
 xlog_assign_atomic_lsn(atomic64_t *lsn, uint cycle, uint block)
 {
     atomic64_set(lsn, xlog_assign_lsn(cycle, block));
 }
 
 /*
  * When we crack the grant head, we sample it first so that the value will not
  * change while we are cracking it into the component values. This means we
  * will always get consistent component values to work from.
  */
 static inline void
 xlog_crack_grant_head_val(int64_t val, int *cycle, int *space)
 {
     *cycle = val >> 32;
     *space = val & 0xffffffff;
 }
 
 static inline void
 xlog_crack_grant_head(atomic64_t *head, int *cycle, int *space)
 {
     xlog_crack_grant_head_val(atomic64_read(head), cycle, space);
 }
 
 static inline int64_t
 xlog_assign_grant_head_val(int cycle, int space)
 {
     return ((int64_t)cycle << 32) | space;
 }
 
 static inline void
 xlog_assign_grant_head(atomic64_t *head, int cycle, int space)
 {
     atomic64_set(head, xlog_assign_grant_head_val(cycle, space));
 }
 
 /*
  * Committed Item List interfaces
  */
 int xlog_cil_init(struct xlog *log);
 void    xlog_cil_init_post_recovery(struct xlog *log);
 void    xlog_cil_destroy(struct xlog *log);
 bool    xlog_cil_empty(struct xlog *log);
 void    xlog_cil_commit(struct xlog *log, struct xfs_trans *tp,
             xfs_csn_t *commit_seq, bool regrant);
 void    xlog_cil_set_ctx_write_state(struct xfs_cil_ctx *ctx,
             struct xlog_in_core *iclog);
 
 
 /*
  * CIL force routines
  */
 void xlog_cil_flush(struct xlog *log);
 xfs_lsn_t xlog_cil_force_seq(struct xlog *log, xfs_csn_t sequence);
 
 static inline void
 xlog_cil_force(struct xlog *log)
 {
     xlog_cil_force_seq(log, log->l_cilp->xc_current_sequence);
 }
 
 /*
  * Wrapper function for waiting on a wait queue serialised against wakeups
  * by a spinlock. This matches the semantics of all the wait queues used in the
  * log code.
  */
 static inline void
 xlog_wait(
     struct wait_queue_head  *wq,
     struct spinlock     *lock)
         __releases(lock)
 {
     DECLARE_WAITQUEUE(wait, current);
 
     add_wait_queue_exclusive(wq, &wait);
     __set_current_state(TASK_UNINTERRUPTIBLE);
     spin_unlock(lock);
     schedule();
     remove_wait_queue(wq, &wait);
 }
 
 int xlog_wait_on_iclog(struct xlog_in_core *iclog);
 
 /*
  * The LSN is valid so long as it is behind the current LSN. If it isn't, this
  * means that the next log record that includes this metadata could have a
  * smaller LSN. In turn, this means that the modification in the log would not
  * replay.
  */
 static inline bool
 xlog_valid_lsn(
     struct xlog *log,
     xfs_lsn_t   lsn)
 {
     int     cur_cycle;
     int     cur_block;
     bool        valid = true;
 
     /*
      * First, sample the current lsn without locking to avoid added
      * contention from metadata I/O. The current cycle and block are updated
      * (in xlog_state_switch_iclogs()) and read here in a particular order
      * to avoid false negatives (e.g., thinking the metadata LSN is valid
      * when it is not).
      *
      * The current block is always rewound before the cycle is bumped in
      * xlog_state_switch_iclogs() to ensure the current LSN is never seen in
      * a transiently forward state. Instead, we can see the LSN in a
      * transiently behind state if we happen to race with a cycle wrap.
      */
     cur_cycle = READ_ONCE(log->l_curr_cycle);
     smp_rmb();
     cur_block = READ_ONCE(log->l_curr_block);
 
     if ((CYCLE_LSN(lsn) > cur_cycle) ||
         (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block)) {
         /*
          * If the metadata LSN appears invalid, it's possible the check
          * above raced with a wrap to the next log cycle. Grab the lock
          * to check for sure.
          */
         spin_lock(&log->l_icloglock);
         cur_cycle = log->l_curr_cycle;
         cur_block = log->l_curr_block;
         spin_unlock(&log->l_icloglock);
 
         if ((CYCLE_LSN(lsn) > cur_cycle) ||
             (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block))
             valid = false;
     }
 
     return valid;
 }
 
 /*
  * Log vector and shadow buffers can be large, so we need to use kvmalloc() here
  * to ensure success. Unfortunately, kvmalloc() only allows GFP_KERNEL contexts
  * to fall back to vmalloc, so we can't actually do anything useful with gfp
  * flags to control the kmalloc() behaviour within kvmalloc(). Hence kmalloc()
  * will do direct reclaim and compaction in the slow path, both of which are
  * horrendously expensive. We just want kmalloc to fail fast and fall back to
  * vmalloc if it can't get somethign straight away from the free lists or
  * buddy allocator. Hence we have to open code kvmalloc outselves here.
  *
  * This assumes that the caller uses memalloc_nofs_save task context here, so
  * despite the use of GFP_KERNEL here, we are going to be doing GFP_NOFS
  * allocations. This is actually the only way to make vmalloc() do GFP_NOFS
  * allocations, so lets just all pretend this is a GFP_KERNEL context
  * operation....
  */
 static inline void *
 xlog_kvmalloc(
     size_t      buf_size)
 {
     gfp_t       flags = GFP_KERNEL;
     void        *p;
 
     flags &= ~__GFP_DIRECT_RECLAIM;
     flags |= __GFP_NOWARN | __GFP_NORETRY;
     do {
         p = kmalloc(buf_size, flags);
         if (!p)
             p = vmalloc(buf_size);
     } while (!p);
 
     return p;
 }
 
 /*
  * CIL CPU dead notifier
  */
 void xlog_cil_pcp_dead(struct xlog *log, unsigned int cpu);
 
 #endif  /* __XFS_LOG_PRIV_H__ */

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