1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
4  * All Rights Reserved.
5  */
6 #ifndef	__XFS_LOG_PRIV_H__
7 #define __XFS_LOG_PRIV_H__
8 
9 struct xfs_buf;
10 struct xlog;
11 struct xlog_ticket;
12 struct xfs_mount;
13 struct xfs_log_callback;
14 
15 /*
16  * Flags for log structure
17  */
18 #define XLOG_ACTIVE_RECOVERY	0x2	/* in the middle of recovery */
19 #define	XLOG_RECOVERY_NEEDED	0x4	/* log was recovered */
20 #define XLOG_IO_ERROR		0x8	/* log hit an I/O error, and being
21 					   shutdown */
22 #define XLOG_TAIL_WARN		0x10	/* log tail verify warning issued */
23 
24 /*
25  * get client id from packed copy.
26  *
27  * this hack is here because the xlog_pack code copies four bytes
28  * of xlog_op_header containing the fields oh_clientid, oh_flags
29  * and oh_res2 into the packed copy.
30  *
31  * later on this four byte chunk is treated as an int and the
32  * client id is pulled out.
33  *
34  * this has endian issues, of course.
35  */
xlog_get_client_id(__be32 i)36 static inline uint xlog_get_client_id(__be32 i)
37 {
38 	return be32_to_cpu(i) >> 24;
39 }
40 
41 /*
42  * In core log state
43  */
44 #define XLOG_STATE_ACTIVE    0x0001 /* Current IC log being written to */
45 #define XLOG_STATE_WANT_SYNC 0x0002 /* Want to sync this iclog; no more writes */
46 #define XLOG_STATE_SYNCING   0x0004 /* This IC log is syncing */
47 #define XLOG_STATE_DONE_SYNC 0x0008 /* Done syncing to disk */
48 #define XLOG_STATE_DO_CALLBACK \
49 			     0x0010 /* Process callback functions */
50 #define XLOG_STATE_CALLBACK  0x0020 /* Callback functions now */
51 #define XLOG_STATE_DIRTY     0x0040 /* Dirty IC log, not ready for ACTIVE status*/
52 #define XLOG_STATE_IOERROR   0x0080 /* IO error happened in sync'ing log */
53 #define XLOG_STATE_IOABORT   0x0100 /* force abort on I/O completion (debug) */
54 #define XLOG_STATE_ALL	     0x7FFF /* All possible valid flags */
55 #define XLOG_STATE_NOTUSED   0x8000 /* This IC log not being used */
56 
57 /*
58  * Flags to log ticket
59  */
60 #define XLOG_TIC_INITED		0x1	/* has been initialized */
61 #define XLOG_TIC_PERM_RESERV	0x2	/* permanent reservation */
62 
63 #define XLOG_TIC_FLAGS \
64 	{ XLOG_TIC_INITED,	"XLOG_TIC_INITED" }, \
65 	{ XLOG_TIC_PERM_RESERV,	"XLOG_TIC_PERM_RESERV" }
66 
67 /*
68  * Below are states for covering allocation transactions.
69  * By covering, we mean changing the h_tail_lsn in the last on-disk
70  * log write such that no allocation transactions will be re-done during
71  * recovery after a system crash. Recovery starts at the last on-disk
72  * log write.
73  *
74  * These states are used to insert dummy log entries to cover
75  * space allocation transactions which can undo non-transactional changes
76  * after a crash. Writes to a file with space
77  * already allocated do not result in any transactions. Allocations
78  * might include space beyond the EOF. So if we just push the EOF a
79  * little, the last transaction for the file could contain the wrong
80  * size. If there is no file system activity, after an allocation
81  * transaction, and the system crashes, the allocation transaction
82  * will get replayed and the file will be truncated. This could
83  * be hours/days/... after the allocation occurred.
84  *
85  * The fix for this is to do two dummy transactions when the
86  * system is idle. We need two dummy transaction because the h_tail_lsn
87  * in the log record header needs to point beyond the last possible
88  * non-dummy transaction. The first dummy changes the h_tail_lsn to
89  * the first transaction before the dummy. The second dummy causes
90  * h_tail_lsn to point to the first dummy. Recovery starts at h_tail_lsn.
91  *
92  * These dummy transactions get committed when everything
93  * is idle (after there has been some activity).
94  *
95  * There are 5 states used to control this.
96  *
97  *  IDLE -- no logging has been done on the file system or
98  *		we are done covering previous transactions.
99  *  NEED -- logging has occurred and we need a dummy transaction
100  *		when the log becomes idle.
101  *  DONE -- we were in the NEED state and have committed a dummy
102  *		transaction.
103  *  NEED2 -- we detected that a dummy transaction has gone to the
104  *		on disk log with no other transactions.
105  *  DONE2 -- we committed a dummy transaction when in the NEED2 state.
106  *
107  * There are two places where we switch states:
108  *
109  * 1.) In xfs_sync, when we detect an idle log and are in NEED or NEED2.
110  *	We commit the dummy transaction and switch to DONE or DONE2,
111  *	respectively. In all other states, we don't do anything.
112  *
113  * 2.) When we finish writing the on-disk log (xlog_state_clean_log).
114  *
115  *	No matter what state we are in, if this isn't the dummy
116  *	transaction going out, the next state is NEED.
117  *	So, if we aren't in the DONE or DONE2 states, the next state
118  *	is NEED. We can't be finishing a write of the dummy record
119  *	unless it was committed and the state switched to DONE or DONE2.
120  *
121  *	If we are in the DONE state and this was a write of the
122  *		dummy transaction, we move to NEED2.
123  *
124  *	If we are in the DONE2 state and this was a write of the
125  *		dummy transaction, we move to IDLE.
126  *
127  *
128  * Writing only one dummy transaction can get appended to
129  * one file space allocation. When this happens, the log recovery
130  * code replays the space allocation and a file could be truncated.
131  * This is why we have the NEED2 and DONE2 states before going idle.
132  */
133 
134 #define XLOG_STATE_COVER_IDLE	0
135 #define XLOG_STATE_COVER_NEED	1
136 #define XLOG_STATE_COVER_DONE	2
137 #define XLOG_STATE_COVER_NEED2	3
138 #define XLOG_STATE_COVER_DONE2	4
139 
140 #define XLOG_COVER_OPS		5
141 
142 /* Ticket reservation region accounting */
143 #define XLOG_TIC_LEN_MAX	15
144 
145 /*
146  * Reservation region
147  * As would be stored in xfs_log_iovec but without the i_addr which
148  * we don't care about.
149  */
150 typedef struct xlog_res {
151 	uint	r_len;	/* region length		:4 */
152 	uint	r_type;	/* region's transaction type	:4 */
153 } xlog_res_t;
154 
155 typedef struct xlog_ticket {
156 	struct list_head   t_queue;	 /* reserve/write queue */
157 	struct task_struct *t_task;	 /* task that owns this ticket */
158 	xlog_tid_t	   t_tid;	 /* transaction identifier	 : 4  */
159 	atomic_t	   t_ref;	 /* ticket reference count       : 4  */
160 	int		   t_curr_res;	 /* current reservation in bytes : 4  */
161 	int		   t_unit_res;	 /* unit reservation in bytes    : 4  */
162 	char		   t_ocnt;	 /* original count		 : 1  */
163 	char		   t_cnt;	 /* current count		 : 1  */
164 	char		   t_clientid;	 /* who does this belong to;	 : 1  */
165 	char		   t_flags;	 /* properties of reservation	 : 1  */
166 
167         /* reservation array fields */
168 	uint		   t_res_num;                    /* num in array : 4 */
169 	uint		   t_res_num_ophdrs;		 /* num op hdrs  : 4 */
170 	uint		   t_res_arr_sum;		 /* array sum    : 4 */
171 	uint		   t_res_o_flow;		 /* sum overflow : 4 */
172 	xlog_res_t	   t_res_arr[XLOG_TIC_LEN_MAX];  /* array of res : 8 * 15 */
173 } xlog_ticket_t;
174 
175 /*
176  * - A log record header is 512 bytes.  There is plenty of room to grow the
177  *	xlog_rec_header_t into the reserved space.
178  * - ic_data follows, so a write to disk can start at the beginning of
179  *	the iclog.
180  * - ic_forcewait is used to implement synchronous forcing of the iclog to disk.
181  * - ic_next is the pointer to the next iclog in the ring.
182  * - ic_bp is a pointer to the buffer used to write this incore log to disk.
183  * - ic_log is a pointer back to the global log structure.
184  * - ic_callback is a linked list of callback function/argument pairs to be
185  *	called after an iclog finishes writing.
186  * - ic_size is the full size of the header plus data.
187  * - ic_offset is the current number of bytes written to in this iclog.
188  * - ic_refcnt is bumped when someone is writing to the log.
189  * - ic_state is the state of the iclog.
190  *
191  * Because of cacheline contention on large machines, we need to separate
192  * various resources onto different cachelines. To start with, make the
193  * structure cacheline aligned. The following fields can be contended on
194  * by independent processes:
195  *
196  *	- ic_callback_*
197  *	- ic_refcnt
198  *	- fields protected by the global l_icloglock
199  *
200  * so we need to ensure that these fields are located in separate cachelines.
201  * We'll put all the read-only and l_icloglock fields in the first cacheline,
202  * and move everything else out to subsequent cachelines.
203  */
204 typedef struct xlog_in_core {
205 	wait_queue_head_t	ic_force_wait;
206 	wait_queue_head_t	ic_write_wait;
207 	struct xlog_in_core	*ic_next;
208 	struct xlog_in_core	*ic_prev;
209 	struct xfs_buf		*ic_bp;
210 	struct xlog		*ic_log;
211 	int			ic_size;
212 	int			ic_offset;
213 	int			ic_bwritecnt;
214 	unsigned short		ic_state;
215 	char			*ic_datap;	/* pointer to iclog data */
216 
217 	/* Callback structures need their own cacheline */
218 	spinlock_t		ic_callback_lock ____cacheline_aligned_in_smp;
219 	struct xfs_log_callback	*ic_callback;
220 	struct xfs_log_callback	**ic_callback_tail;
221 
222 	/* reference counts need their own cacheline */
223 	atomic_t		ic_refcnt ____cacheline_aligned_in_smp;
224 	xlog_in_core_2_t	*ic_data;
225 #define ic_header	ic_data->hic_header
226 } xlog_in_core_t;
227 
228 /*
229  * The CIL context is used to aggregate per-transaction details as well be
230  * passed to the iclog for checkpoint post-commit processing.  After being
231  * passed to the iclog, another context needs to be allocated for tracking the
232  * next set of transactions to be aggregated into a checkpoint.
233  */
234 struct xfs_cil;
235 
236 struct xfs_cil_ctx {
237 	struct xfs_cil		*cil;
238 	xfs_lsn_t		sequence;	/* chkpt sequence # */
239 	xfs_lsn_t		start_lsn;	/* first LSN of chkpt commit */
240 	xfs_lsn_t		commit_lsn;	/* chkpt commit record lsn */
241 	struct xlog_ticket	*ticket;	/* chkpt ticket */
242 	int			nvecs;		/* number of regions */
243 	int			space_used;	/* aggregate size of regions */
244 	struct list_head	busy_extents;	/* busy extents in chkpt */
245 	struct xfs_log_vec	*lv_chain;	/* logvecs being pushed */
246 	struct xfs_log_callback	log_cb;		/* completion callback hook. */
247 	struct list_head	committing;	/* ctx committing list */
248 	struct work_struct	discard_endio_work;
249 };
250 
251 /*
252  * Committed Item List structure
253  *
254  * This structure is used to track log items that have been committed but not
255  * yet written into the log. It is used only when the delayed logging mount
256  * option is enabled.
257  *
258  * This structure tracks the list of committing checkpoint contexts so
259  * we can avoid the problem of having to hold out new transactions during a
260  * flush until we have a the commit record LSN of the checkpoint. We can
261  * traverse the list of committing contexts in xlog_cil_push_lsn() to find a
262  * sequence match and extract the commit LSN directly from there. If the
263  * checkpoint is still in the process of committing, we can block waiting for
264  * the commit LSN to be determined as well. This should make synchronous
265  * operations almost as efficient as the old logging methods.
266  */
267 struct xfs_cil {
268 	struct xlog		*xc_log;
269 	struct list_head	xc_cil;
270 	spinlock_t		xc_cil_lock;
271 
272 	struct rw_semaphore	xc_ctx_lock ____cacheline_aligned_in_smp;
273 	struct xfs_cil_ctx	*xc_ctx;
274 
275 	spinlock_t		xc_push_lock ____cacheline_aligned_in_smp;
276 	xfs_lsn_t		xc_push_seq;
277 	struct list_head	xc_committing;
278 	wait_queue_head_t	xc_commit_wait;
279 	xfs_lsn_t		xc_current_sequence;
280 	struct work_struct	xc_push_work;
281 } ____cacheline_aligned_in_smp;
282 
283 /*
284  * The amount of log space we allow the CIL to aggregate is difficult to size.
285  * Whatever we choose, we have to make sure we can get a reservation for the
286  * log space effectively, that it is large enough to capture sufficient
287  * relogging to reduce log buffer IO significantly, but it is not too large for
288  * the log or induces too much latency when writing out through the iclogs. We
289  * track both space consumed and the number of vectors in the checkpoint
290  * context, so we need to decide which to use for limiting.
291  *
292  * Every log buffer we write out during a push needs a header reserved, which
293  * is at least one sector and more for v2 logs. Hence we need a reservation of
294  * at least 512 bytes per 32k of log space just for the LR headers. That means
295  * 16KB of reservation per megabyte of delayed logging space we will consume,
296  * plus various headers.  The number of headers will vary based on the num of
297  * io vectors, so limiting on a specific number of vectors is going to result
298  * in transactions of varying size. IOWs, it is more consistent to track and
299  * limit space consumed in the log rather than by the number of objects being
300  * logged in order to prevent checkpoint ticket overruns.
301  *
302  * Further, use of static reservations through the log grant mechanism is
303  * problematic. It introduces a lot of complexity (e.g. reserve grant vs write
304  * grant) and a significant deadlock potential because regranting write space
305  * can block on log pushes. Hence if we have to regrant log space during a log
306  * push, we can deadlock.
307  *
308  * However, we can avoid this by use of a dynamic "reservation stealing"
309  * technique during transaction commit whereby unused reservation space in the
310  * transaction ticket is transferred to the CIL ctx commit ticket to cover the
311  * space needed by the checkpoint transaction. This means that we never need to
312  * specifically reserve space for the CIL checkpoint transaction, nor do we
313  * need to regrant space once the checkpoint completes. This also means the
314  * checkpoint transaction ticket is specific to the checkpoint context, rather
315  * than the CIL itself.
316  *
317  * With dynamic reservations, we can effectively make up arbitrary limits for
318  * the checkpoint size so long as they don't violate any other size rules.
319  * Recovery imposes a rule that no transaction exceed half the log, so we are
320  * limited by that.  Furthermore, the log transaction reservation subsystem
321  * tries to keep 25% of the log free, so we need to keep below that limit or we
322  * risk running out of free log space to start any new transactions.
323  *
324  * In order to keep background CIL push efficient, we will set a lower
325  * threshold at which background pushing is attempted without blocking current
326  * transaction commits.  A separate, higher bound defines when CIL pushes are
327  * enforced to ensure we stay within our maximum checkpoint size bounds.
328  * threshold, yet give us plenty of space for aggregation on large logs.
329  */
330 #define XLOG_CIL_SPACE_LIMIT(log)	(log->l_logsize >> 3)
331 
332 /*
333  * ticket grant locks, queues and accounting have their own cachlines
334  * as these are quite hot and can be operated on concurrently.
335  */
336 struct xlog_grant_head {
337 	spinlock_t		lock ____cacheline_aligned_in_smp;
338 	struct list_head	waiters;
339 	atomic64_t		grant;
340 };
341 
342 /*
343  * The reservation head lsn is not made up of a cycle number and block number.
344  * Instead, it uses a cycle number and byte number.  Logs don't expect to
345  * overflow 31 bits worth of byte offset, so using a byte number will mean
346  * that round off problems won't occur when releasing partial reservations.
347  */
348 struct xlog {
349 	/* The following fields don't need locking */
350 	struct xfs_mount	*l_mp;	        /* mount point */
351 	struct xfs_ail		*l_ailp;	/* AIL log is working with */
352 	struct xfs_cil		*l_cilp;	/* CIL log is working with */
353 	struct xfs_buf		*l_xbuf;        /* extra buffer for log
354 						 * wrapping */
355 	struct xfs_buftarg	*l_targ;        /* buftarg of log */
356 	struct delayed_work	l_work;		/* background flush work */
357 	uint			l_flags;
358 	uint			l_quotaoffs_flag; /* XFS_DQ_*, for QUOTAOFFs */
359 	struct list_head	*l_buf_cancel_table;
360 	int			l_iclog_hsize;  /* size of iclog header */
361 	int			l_iclog_heads;  /* # of iclog header sectors */
362 	uint			l_sectBBsize;   /* sector size in BBs (2^n) */
363 	int			l_iclog_size;	/* size of log in bytes */
364 	int			l_iclog_size_log; /* log power size of log */
365 	int			l_iclog_bufs;	/* number of iclog buffers */
366 	xfs_daddr_t		l_logBBstart;   /* start block of log */
367 	int			l_logsize;      /* size of log in bytes */
368 	int			l_logBBsize;    /* size of log in BB chunks */
369 
370 	/* The following block of fields are changed while holding icloglock */
371 	wait_queue_head_t	l_flush_wait ____cacheline_aligned_in_smp;
372 						/* waiting for iclog flush */
373 	int			l_covered_state;/* state of "covering disk
374 						 * log entries" */
375 	xlog_in_core_t		*l_iclog;       /* head log queue	*/
376 	spinlock_t		l_icloglock;    /* grab to change iclog state */
377 	int			l_curr_cycle;   /* Cycle number of log writes */
378 	int			l_prev_cycle;   /* Cycle number before last
379 						 * block increment */
380 	int			l_curr_block;   /* current logical log block */
381 	int			l_prev_block;   /* previous logical log block */
382 
383 	/*
384 	 * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and
385 	 * read without needing to hold specific locks. To avoid operations
386 	 * contending with other hot objects, place each of them on a separate
387 	 * cacheline.
388 	 */
389 	/* lsn of last LR on disk */
390 	atomic64_t		l_last_sync_lsn ____cacheline_aligned_in_smp;
391 	/* lsn of 1st LR with unflushed * buffers */
392 	atomic64_t		l_tail_lsn ____cacheline_aligned_in_smp;
393 
394 	struct xlog_grant_head	l_reserve_head;
395 	struct xlog_grant_head	l_write_head;
396 
397 	struct xfs_kobj		l_kobj;
398 
399 	/* The following field are used for debugging; need to hold icloglock */
400 #ifdef DEBUG
401 	void			*l_iclog_bak[XLOG_MAX_ICLOGS];
402 	/* log record crc error injection factor */
403 	uint32_t		l_badcrc_factor;
404 #endif
405 	/* log recovery lsn tracking (for buffer submission */
406 	xfs_lsn_t		l_recovery_lsn;
407 };
408 
409 #define XLOG_BUF_CANCEL_BUCKET(log, blkno) \
410 	((log)->l_buf_cancel_table + ((uint64_t)blkno % XLOG_BC_TABLE_SIZE))
411 
412 #define XLOG_FORCED_SHUTDOWN(log)	((log)->l_flags & XLOG_IO_ERROR)
413 
414 /* common routines */
415 extern int
416 xlog_recover(
417 	struct xlog		*log);
418 extern int
419 xlog_recover_finish(
420 	struct xlog		*log);
421 extern int
422 xlog_recover_cancel(struct xlog *);
423 
424 extern __le32	 xlog_cksum(struct xlog *log, struct xlog_rec_header *rhead,
425 			    char *dp, int size);
426 
427 extern kmem_zone_t *xfs_log_ticket_zone;
428 struct xlog_ticket *
429 xlog_ticket_alloc(
430 	struct xlog	*log,
431 	int		unit_bytes,
432 	int		count,
433 	char		client,
434 	bool		permanent,
435 	xfs_km_flags_t	alloc_flags);
436 
437 
438 static inline void
xlog_write_adv_cnt(void ** ptr,int * len,int * off,size_t bytes)439 xlog_write_adv_cnt(void **ptr, int *len, int *off, size_t bytes)
440 {
441 	*ptr += bytes;
442 	*len -= bytes;
443 	*off += bytes;
444 }
445 
446 void	xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
447 void	xlog_print_trans(struct xfs_trans *);
448 int
449 xlog_write(
450 	struct xlog		*log,
451 	struct xfs_log_vec	*log_vector,
452 	struct xlog_ticket	*tic,
453 	xfs_lsn_t		*start_lsn,
454 	struct xlog_in_core	**commit_iclog,
455 	uint			flags);
456 
457 /*
458  * When we crack an atomic LSN, we sample it first so that the value will not
459  * change while we are cracking it into the component values. This means we
460  * will always get consistent component values to work from. This should always
461  * be used to sample and crack LSNs that are stored and updated in atomic
462  * variables.
463  */
464 static inline void
xlog_crack_atomic_lsn(atomic64_t * lsn,uint * cycle,uint * block)465 xlog_crack_atomic_lsn(atomic64_t *lsn, uint *cycle, uint *block)
466 {
467 	xfs_lsn_t val = atomic64_read(lsn);
468 
469 	*cycle = CYCLE_LSN(val);
470 	*block = BLOCK_LSN(val);
471 }
472 
473 /*
474  * Calculate and assign a value to an atomic LSN variable from component pieces.
475  */
476 static inline void
xlog_assign_atomic_lsn(atomic64_t * lsn,uint cycle,uint block)477 xlog_assign_atomic_lsn(atomic64_t *lsn, uint cycle, uint block)
478 {
479 	atomic64_set(lsn, xlog_assign_lsn(cycle, block));
480 }
481 
482 /*
483  * When we crack the grant head, we sample it first so that the value will not
484  * change while we are cracking it into the component values. This means we
485  * will always get consistent component values to work from.
486  */
487 static inline void
xlog_crack_grant_head_val(int64_t val,int * cycle,int * space)488 xlog_crack_grant_head_val(int64_t val, int *cycle, int *space)
489 {
490 	*cycle = val >> 32;
491 	*space = val & 0xffffffff;
492 }
493 
494 static inline void
xlog_crack_grant_head(atomic64_t * head,int * cycle,int * space)495 xlog_crack_grant_head(atomic64_t *head, int *cycle, int *space)
496 {
497 	xlog_crack_grant_head_val(atomic64_read(head), cycle, space);
498 }
499 
500 static inline int64_t
xlog_assign_grant_head_val(int cycle,int space)501 xlog_assign_grant_head_val(int cycle, int space)
502 {
503 	return ((int64_t)cycle << 32) | space;
504 }
505 
506 static inline void
xlog_assign_grant_head(atomic64_t * head,int cycle,int space)507 xlog_assign_grant_head(atomic64_t *head, int cycle, int space)
508 {
509 	atomic64_set(head, xlog_assign_grant_head_val(cycle, space));
510 }
511 
512 /*
513  * Committed Item List interfaces
514  */
515 int	xlog_cil_init(struct xlog *log);
516 void	xlog_cil_init_post_recovery(struct xlog *log);
517 void	xlog_cil_destroy(struct xlog *log);
518 bool	xlog_cil_empty(struct xlog *log);
519 
520 /*
521  * CIL force routines
522  */
523 xfs_lsn_t
524 xlog_cil_force_lsn(
525 	struct xlog *log,
526 	xfs_lsn_t sequence);
527 
528 static inline void
xlog_cil_force(struct xlog * log)529 xlog_cil_force(struct xlog *log)
530 {
531 	xlog_cil_force_lsn(log, log->l_cilp->xc_current_sequence);
532 }
533 
534 /*
535  * Unmount record type is used as a pseudo transaction type for the ticket.
536  * It's value must be outside the range of XFS_TRANS_* values.
537  */
538 #define XLOG_UNMOUNT_REC_TYPE	(-1U)
539 
540 /*
541  * Wrapper function for waiting on a wait queue serialised against wakeups
542  * by a spinlock. This matches the semantics of all the wait queues used in the
543  * log code.
544  */
xlog_wait(wait_queue_head_t * wq,spinlock_t * lock)545 static inline void xlog_wait(wait_queue_head_t *wq, spinlock_t *lock)
546 {
547 	DECLARE_WAITQUEUE(wait, current);
548 
549 	add_wait_queue_exclusive(wq, &wait);
550 	__set_current_state(TASK_UNINTERRUPTIBLE);
551 	spin_unlock(lock);
552 	schedule();
553 	remove_wait_queue(wq, &wait);
554 }
555 
556 /*
557  * The LSN is valid so long as it is behind the current LSN. If it isn't, this
558  * means that the next log record that includes this metadata could have a
559  * smaller LSN. In turn, this means that the modification in the log would not
560  * replay.
561  */
562 static inline bool
xlog_valid_lsn(struct xlog * log,xfs_lsn_t lsn)563 xlog_valid_lsn(
564 	struct xlog	*log,
565 	xfs_lsn_t	lsn)
566 {
567 	int		cur_cycle;
568 	int		cur_block;
569 	bool		valid = true;
570 
571 	/*
572 	 * First, sample the current lsn without locking to avoid added
573 	 * contention from metadata I/O. The current cycle and block are updated
574 	 * (in xlog_state_switch_iclogs()) and read here in a particular order
575 	 * to avoid false negatives (e.g., thinking the metadata LSN is valid
576 	 * when it is not).
577 	 *
578 	 * The current block is always rewound before the cycle is bumped in
579 	 * xlog_state_switch_iclogs() to ensure the current LSN is never seen in
580 	 * a transiently forward state. Instead, we can see the LSN in a
581 	 * transiently behind state if we happen to race with a cycle wrap.
582 	 */
583 	cur_cycle = READ_ONCE(log->l_curr_cycle);
584 	smp_rmb();
585 	cur_block = READ_ONCE(log->l_curr_block);
586 
587 	if ((CYCLE_LSN(lsn) > cur_cycle) ||
588 	    (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block)) {
589 		/*
590 		 * If the metadata LSN appears invalid, it's possible the check
591 		 * above raced with a wrap to the next log cycle. Grab the lock
592 		 * to check for sure.
593 		 */
594 		spin_lock(&log->l_icloglock);
595 		cur_cycle = log->l_curr_cycle;
596 		cur_block = log->l_curr_block;
597 		spin_unlock(&log->l_icloglock);
598 
599 		if ((CYCLE_LSN(lsn) > cur_cycle) ||
600 		    (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block))
601 			valid = false;
602 	}
603 
604 	return valid;
605 }
606 
607 #endif	/* __XFS_LOG_PRIV_H__ */
608