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1 /*
2  * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
3  * All Rights Reserved.
4  *
5  * This program is free software; you can redistribute it and/or
6  * modify it under the terms of the GNU General Public License as
7  * published by the Free Software Foundation.
8  *
9  * This program is distributed in the hope that it would be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write the Free Software Foundation,
16  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
17  */
18 #ifndef	__XFS_LOG_PRIV_H__
19 #define __XFS_LOG_PRIV_H__
20 
21 struct xfs_buf;
22 struct xlog;
23 struct xlog_ticket;
24 struct xfs_mount;
25 struct xfs_log_callback;
26 
27 /*
28  * Flags for log structure
29  */
30 #define XLOG_ACTIVE_RECOVERY	0x2	/* in the middle of recovery */
31 #define	XLOG_RECOVERY_NEEDED	0x4	/* log was recovered */
32 #define XLOG_IO_ERROR		0x8	/* log hit an I/O error, and being
33 					   shutdown */
34 #define XLOG_TAIL_WARN		0x10	/* log tail verify warning issued */
35 
36 /*
37  * get client id from packed copy.
38  *
39  * this hack is here because the xlog_pack code copies four bytes
40  * of xlog_op_header containing the fields oh_clientid, oh_flags
41  * and oh_res2 into the packed copy.
42  *
43  * later on this four byte chunk is treated as an int and the
44  * client id is pulled out.
45  *
46  * this has endian issues, of course.
47  */
xlog_get_client_id(__be32 i)48 static inline uint xlog_get_client_id(__be32 i)
49 {
50 	return be32_to_cpu(i) >> 24;
51 }
52 
53 /*
54  * In core log state
55  */
56 #define XLOG_STATE_ACTIVE    0x0001 /* Current IC log being written to */
57 #define XLOG_STATE_WANT_SYNC 0x0002 /* Want to sync this iclog; no more writes */
58 #define XLOG_STATE_SYNCING   0x0004 /* This IC log is syncing */
59 #define XLOG_STATE_DONE_SYNC 0x0008 /* Done syncing to disk */
60 #define XLOG_STATE_DO_CALLBACK \
61 			     0x0010 /* Process callback functions */
62 #define XLOG_STATE_CALLBACK  0x0020 /* Callback functions now */
63 #define XLOG_STATE_DIRTY     0x0040 /* Dirty IC log, not ready for ACTIVE status*/
64 #define XLOG_STATE_IOERROR   0x0080 /* IO error happened in sync'ing log */
65 #define XLOG_STATE_IOABORT   0x0100 /* force abort on I/O completion (debug) */
66 #define XLOG_STATE_ALL	     0x7FFF /* All possible valid flags */
67 #define XLOG_STATE_NOTUSED   0x8000 /* This IC log not being used */
68 
69 /*
70  * Flags to log ticket
71  */
72 #define XLOG_TIC_INITED		0x1	/* has been initialized */
73 #define XLOG_TIC_PERM_RESERV	0x2	/* permanent reservation */
74 
75 #define XLOG_TIC_FLAGS \
76 	{ XLOG_TIC_INITED,	"XLOG_TIC_INITED" }, \
77 	{ XLOG_TIC_PERM_RESERV,	"XLOG_TIC_PERM_RESERV" }
78 
79 /*
80  * Below are states for covering allocation transactions.
81  * By covering, we mean changing the h_tail_lsn in the last on-disk
82  * log write such that no allocation transactions will be re-done during
83  * recovery after a system crash. Recovery starts at the last on-disk
84  * log write.
85  *
86  * These states are used to insert dummy log entries to cover
87  * space allocation transactions which can undo non-transactional changes
88  * after a crash. Writes to a file with space
89  * already allocated do not result in any transactions. Allocations
90  * might include space beyond the EOF. So if we just push the EOF a
91  * little, the last transaction for the file could contain the wrong
92  * size. If there is no file system activity, after an allocation
93  * transaction, and the system crashes, the allocation transaction
94  * will get replayed and the file will be truncated. This could
95  * be hours/days/... after the allocation occurred.
96  *
97  * The fix for this is to do two dummy transactions when the
98  * system is idle. We need two dummy transaction because the h_tail_lsn
99  * in the log record header needs to point beyond the last possible
100  * non-dummy transaction. The first dummy changes the h_tail_lsn to
101  * the first transaction before the dummy. The second dummy causes
102  * h_tail_lsn to point to the first dummy. Recovery starts at h_tail_lsn.
103  *
104  * These dummy transactions get committed when everything
105  * is idle (after there has been some activity).
106  *
107  * There are 5 states used to control this.
108  *
109  *  IDLE -- no logging has been done on the file system or
110  *		we are done covering previous transactions.
111  *  NEED -- logging has occurred and we need a dummy transaction
112  *		when the log becomes idle.
113  *  DONE -- we were in the NEED state and have committed a dummy
114  *		transaction.
115  *  NEED2 -- we detected that a dummy transaction has gone to the
116  *		on disk log with no other transactions.
117  *  DONE2 -- we committed a dummy transaction when in the NEED2 state.
118  *
119  * There are two places where we switch states:
120  *
121  * 1.) In xfs_sync, when we detect an idle log and are in NEED or NEED2.
122  *	We commit the dummy transaction and switch to DONE or DONE2,
123  *	respectively. In all other states, we don't do anything.
124  *
125  * 2.) When we finish writing the on-disk log (xlog_state_clean_log).
126  *
127  *	No matter what state we are in, if this isn't the dummy
128  *	transaction going out, the next state is NEED.
129  *	So, if we aren't in the DONE or DONE2 states, the next state
130  *	is NEED. We can't be finishing a write of the dummy record
131  *	unless it was committed and the state switched to DONE or DONE2.
132  *
133  *	If we are in the DONE state and this was a write of the
134  *		dummy transaction, we move to NEED2.
135  *
136  *	If we are in the DONE2 state and this was a write of the
137  *		dummy transaction, we move to IDLE.
138  *
139  *
140  * Writing only one dummy transaction can get appended to
141  * one file space allocation. When this happens, the log recovery
142  * code replays the space allocation and a file could be truncated.
143  * This is why we have the NEED2 and DONE2 states before going idle.
144  */
145 
146 #define XLOG_STATE_COVER_IDLE	0
147 #define XLOG_STATE_COVER_NEED	1
148 #define XLOG_STATE_COVER_DONE	2
149 #define XLOG_STATE_COVER_NEED2	3
150 #define XLOG_STATE_COVER_DONE2	4
151 
152 #define XLOG_COVER_OPS		5
153 
154 /* Ticket reservation region accounting */
155 #define XLOG_TIC_LEN_MAX	15
156 
157 /*
158  * Reservation region
159  * As would be stored in xfs_log_iovec but without the i_addr which
160  * we don't care about.
161  */
162 typedef struct xlog_res {
163 	uint	r_len;	/* region length		:4 */
164 	uint	r_type;	/* region's transaction type	:4 */
165 } xlog_res_t;
166 
167 typedef struct xlog_ticket {
168 	struct list_head   t_queue;	 /* reserve/write queue */
169 	struct task_struct *t_task;	 /* task that owns this ticket */
170 	xlog_tid_t	   t_tid;	 /* transaction identifier	 : 4  */
171 	atomic_t	   t_ref;	 /* ticket reference count       : 4  */
172 	int		   t_curr_res;	 /* current reservation in bytes : 4  */
173 	int		   t_unit_res;	 /* unit reservation in bytes    : 4  */
174 	char		   t_ocnt;	 /* original count		 : 1  */
175 	char		   t_cnt;	 /* current count		 : 1  */
176 	char		   t_clientid;	 /* who does this belong to;	 : 1  */
177 	char		   t_flags;	 /* properties of reservation	 : 1  */
178 
179         /* reservation array fields */
180 	uint		   t_res_num;                    /* num in array : 4 */
181 	uint		   t_res_num_ophdrs;		 /* num op hdrs  : 4 */
182 	uint		   t_res_arr_sum;		 /* array sum    : 4 */
183 	uint		   t_res_o_flow;		 /* sum overflow : 4 */
184 	xlog_res_t	   t_res_arr[XLOG_TIC_LEN_MAX];  /* array of res : 8 * 15 */
185 } xlog_ticket_t;
186 
187 /*
188  * - A log record header is 512 bytes.  There is plenty of room to grow the
189  *	xlog_rec_header_t into the reserved space.
190  * - ic_data follows, so a write to disk can start at the beginning of
191  *	the iclog.
192  * - ic_forcewait is used to implement synchronous forcing of the iclog to disk.
193  * - ic_next is the pointer to the next iclog in the ring.
194  * - ic_bp is a pointer to the buffer used to write this incore log to disk.
195  * - ic_log is a pointer back to the global log structure.
196  * - ic_callback is a linked list of callback function/argument pairs to be
197  *	called after an iclog finishes writing.
198  * - ic_size is the full size of the header plus data.
199  * - ic_offset is the current number of bytes written to in this iclog.
200  * - ic_refcnt is bumped when someone is writing to the log.
201  * - ic_state is the state of the iclog.
202  *
203  * Because of cacheline contention on large machines, we need to separate
204  * various resources onto different cachelines. To start with, make the
205  * structure cacheline aligned. The following fields can be contended on
206  * by independent processes:
207  *
208  *	- ic_callback_*
209  *	- ic_refcnt
210  *	- fields protected by the global l_icloglock
211  *
212  * so we need to ensure that these fields are located in separate cachelines.
213  * We'll put all the read-only and l_icloglock fields in the first cacheline,
214  * and move everything else out to subsequent cachelines.
215  */
216 typedef struct xlog_in_core {
217 	wait_queue_head_t	ic_force_wait;
218 	wait_queue_head_t	ic_write_wait;
219 	struct xlog_in_core	*ic_next;
220 	struct xlog_in_core	*ic_prev;
221 	struct xfs_buf		*ic_bp;
222 	struct xlog		*ic_log;
223 	int			ic_size;
224 	int			ic_offset;
225 	int			ic_bwritecnt;
226 	unsigned short		ic_state;
227 	char			*ic_datap;	/* pointer to iclog data */
228 
229 	/* Callback structures need their own cacheline */
230 	spinlock_t		ic_callback_lock ____cacheline_aligned_in_smp;
231 	struct xfs_log_callback	*ic_callback;
232 	struct xfs_log_callback	**ic_callback_tail;
233 
234 	/* reference counts need their own cacheline */
235 	atomic_t		ic_refcnt ____cacheline_aligned_in_smp;
236 	xlog_in_core_2_t	*ic_data;
237 #define ic_header	ic_data->hic_header
238 } xlog_in_core_t;
239 
240 /*
241  * The CIL context is used to aggregate per-transaction details as well be
242  * passed to the iclog for checkpoint post-commit processing.  After being
243  * passed to the iclog, another context needs to be allocated for tracking the
244  * next set of transactions to be aggregated into a checkpoint.
245  */
246 struct xfs_cil;
247 
248 struct xfs_cil_ctx {
249 	struct xfs_cil		*cil;
250 	xfs_lsn_t		sequence;	/* chkpt sequence # */
251 	xfs_lsn_t		start_lsn;	/* first LSN of chkpt commit */
252 	xfs_lsn_t		commit_lsn;	/* chkpt commit record lsn */
253 	struct xlog_ticket	*ticket;	/* chkpt ticket */
254 	int			nvecs;		/* number of regions */
255 	int			space_used;	/* aggregate size of regions */
256 	struct list_head	busy_extents;	/* busy extents in chkpt */
257 	struct xfs_log_vec	*lv_chain;	/* logvecs being pushed */
258 	struct xfs_log_callback	log_cb;		/* completion callback hook. */
259 	struct list_head	committing;	/* ctx committing list */
260 };
261 
262 /*
263  * Committed Item List structure
264  *
265  * This structure is used to track log items that have been committed but not
266  * yet written into the log. It is used only when the delayed logging mount
267  * option is enabled.
268  *
269  * This structure tracks the list of committing checkpoint contexts so
270  * we can avoid the problem of having to hold out new transactions during a
271  * flush until we have a the commit record LSN of the checkpoint. We can
272  * traverse the list of committing contexts in xlog_cil_push_lsn() to find a
273  * sequence match and extract the commit LSN directly from there. If the
274  * checkpoint is still in the process of committing, we can block waiting for
275  * the commit LSN to be determined as well. This should make synchronous
276  * operations almost as efficient as the old logging methods.
277  */
278 struct xfs_cil {
279 	struct xlog		*xc_log;
280 	struct list_head	xc_cil;
281 	spinlock_t		xc_cil_lock;
282 
283 	struct rw_semaphore	xc_ctx_lock ____cacheline_aligned_in_smp;
284 	struct xfs_cil_ctx	*xc_ctx;
285 
286 	spinlock_t		xc_push_lock ____cacheline_aligned_in_smp;
287 	xfs_lsn_t		xc_push_seq;
288 	struct list_head	xc_committing;
289 	wait_queue_head_t	xc_commit_wait;
290 	xfs_lsn_t		xc_current_sequence;
291 	struct work_struct	xc_push_work;
292 } ____cacheline_aligned_in_smp;
293 
294 /*
295  * The amount of log space we allow the CIL to aggregate is difficult to size.
296  * Whatever we choose, we have to make sure we can get a reservation for the
297  * log space effectively, that it is large enough to capture sufficient
298  * relogging to reduce log buffer IO significantly, but it is not too large for
299  * the log or induces too much latency when writing out through the iclogs. We
300  * track both space consumed and the number of vectors in the checkpoint
301  * context, so we need to decide which to use for limiting.
302  *
303  * Every log buffer we write out during a push needs a header reserved, which
304  * is at least one sector and more for v2 logs. Hence we need a reservation of
305  * at least 512 bytes per 32k of log space just for the LR headers. That means
306  * 16KB of reservation per megabyte of delayed logging space we will consume,
307  * plus various headers.  The number of headers will vary based on the num of
308  * io vectors, so limiting on a specific number of vectors is going to result
309  * in transactions of varying size. IOWs, it is more consistent to track and
310  * limit space consumed in the log rather than by the number of objects being
311  * logged in order to prevent checkpoint ticket overruns.
312  *
313  * Further, use of static reservations through the log grant mechanism is
314  * problematic. It introduces a lot of complexity (e.g. reserve grant vs write
315  * grant) and a significant deadlock potential because regranting write space
316  * can block on log pushes. Hence if we have to regrant log space during a log
317  * push, we can deadlock.
318  *
319  * However, we can avoid this by use of a dynamic "reservation stealing"
320  * technique during transaction commit whereby unused reservation space in the
321  * transaction ticket is transferred to the CIL ctx commit ticket to cover the
322  * space needed by the checkpoint transaction. This means that we never need to
323  * specifically reserve space for the CIL checkpoint transaction, nor do we
324  * need to regrant space once the checkpoint completes. This also means the
325  * checkpoint transaction ticket is specific to the checkpoint context, rather
326  * than the CIL itself.
327  *
328  * With dynamic reservations, we can effectively make up arbitrary limits for
329  * the checkpoint size so long as they don't violate any other size rules.
330  * Recovery imposes a rule that no transaction exceed half the log, so we are
331  * limited by that.  Furthermore, the log transaction reservation subsystem
332  * tries to keep 25% of the log free, so we need to keep below that limit or we
333  * risk running out of free log space to start any new transactions.
334  *
335  * In order to keep background CIL push efficient, we will set a lower
336  * threshold at which background pushing is attempted without blocking current
337  * transaction commits.  A separate, higher bound defines when CIL pushes are
338  * enforced to ensure we stay within our maximum checkpoint size bounds.
339  * threshold, yet give us plenty of space for aggregation on large logs.
340  */
341 #define XLOG_CIL_SPACE_LIMIT(log)	(log->l_logsize >> 3)
342 
343 /*
344  * ticket grant locks, queues and accounting have their own cachlines
345  * as these are quite hot and can be operated on concurrently.
346  */
347 struct xlog_grant_head {
348 	spinlock_t		lock ____cacheline_aligned_in_smp;
349 	struct list_head	waiters;
350 	atomic64_t		grant;
351 };
352 
353 /*
354  * The reservation head lsn is not made up of a cycle number and block number.
355  * Instead, it uses a cycle number and byte number.  Logs don't expect to
356  * overflow 31 bits worth of byte offset, so using a byte number will mean
357  * that round off problems won't occur when releasing partial reservations.
358  */
359 struct xlog {
360 	/* The following fields don't need locking */
361 	struct xfs_mount	*l_mp;	        /* mount point */
362 	struct xfs_ail		*l_ailp;	/* AIL log is working with */
363 	struct xfs_cil		*l_cilp;	/* CIL log is working with */
364 	struct xfs_buf		*l_xbuf;        /* extra buffer for log
365 						 * wrapping */
366 	struct xfs_buftarg	*l_targ;        /* buftarg of log */
367 	struct delayed_work	l_work;		/* background flush work */
368 	uint			l_flags;
369 	uint			l_quotaoffs_flag; /* XFS_DQ_*, for QUOTAOFFs */
370 	struct list_head	*l_buf_cancel_table;
371 	int			l_iclog_hsize;  /* size of iclog header */
372 	int			l_iclog_heads;  /* # of iclog header sectors */
373 	uint			l_sectBBsize;   /* sector size in BBs (2^n) */
374 	int			l_iclog_size;	/* size of log in bytes */
375 	int			l_iclog_size_log; /* log power size of log */
376 	int			l_iclog_bufs;	/* number of iclog buffers */
377 	xfs_daddr_t		l_logBBstart;   /* start block of log */
378 	int			l_logsize;      /* size of log in bytes */
379 	int			l_logBBsize;    /* size of log in BB chunks */
380 
381 	/* The following block of fields are changed while holding icloglock */
382 	wait_queue_head_t	l_flush_wait ____cacheline_aligned_in_smp;
383 						/* waiting for iclog flush */
384 	int			l_covered_state;/* state of "covering disk
385 						 * log entries" */
386 	xlog_in_core_t		*l_iclog;       /* head log queue	*/
387 	spinlock_t		l_icloglock;    /* grab to change iclog state */
388 	int			l_curr_cycle;   /* Cycle number of log writes */
389 	int			l_prev_cycle;   /* Cycle number before last
390 						 * block increment */
391 	int			l_curr_block;   /* current logical log block */
392 	int			l_prev_block;   /* previous logical log block */
393 
394 	/*
395 	 * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and
396 	 * read without needing to hold specific locks. To avoid operations
397 	 * contending with other hot objects, place each of them on a separate
398 	 * cacheline.
399 	 */
400 	/* lsn of last LR on disk */
401 	atomic64_t		l_last_sync_lsn ____cacheline_aligned_in_smp;
402 	/* lsn of 1st LR with unflushed * buffers */
403 	atomic64_t		l_tail_lsn ____cacheline_aligned_in_smp;
404 
405 	struct xlog_grant_head	l_reserve_head;
406 	struct xlog_grant_head	l_write_head;
407 
408 	struct xfs_kobj		l_kobj;
409 
410 	/* The following field are used for debugging; need to hold icloglock */
411 #ifdef DEBUG
412 	void			*l_iclog_bak[XLOG_MAX_ICLOGS];
413 	/* log record crc error injection factor */
414 	uint32_t		l_badcrc_factor;
415 #endif
416 	/* log recovery lsn tracking (for buffer submission */
417 	xfs_lsn_t		l_recovery_lsn;
418 };
419 
420 #define XLOG_BUF_CANCEL_BUCKET(log, blkno) \
421 	((log)->l_buf_cancel_table + ((__uint64_t)blkno % XLOG_BC_TABLE_SIZE))
422 
423 #define XLOG_FORCED_SHUTDOWN(log)	((log)->l_flags & XLOG_IO_ERROR)
424 
425 /* common routines */
426 extern int
427 xlog_recover(
428 	struct xlog		*log);
429 extern int
430 xlog_recover_finish(
431 	struct xlog		*log);
432 extern int
433 xlog_recover_cancel(struct xlog *);
434 
435 extern __le32	 xlog_cksum(struct xlog *log, struct xlog_rec_header *rhead,
436 			    char *dp, int size);
437 
438 extern kmem_zone_t *xfs_log_ticket_zone;
439 struct xlog_ticket *
440 xlog_ticket_alloc(
441 	struct xlog	*log,
442 	int		unit_bytes,
443 	int		count,
444 	char		client,
445 	bool		permanent,
446 	xfs_km_flags_t	alloc_flags);
447 
448 
449 static inline void
xlog_write_adv_cnt(void ** ptr,int * len,int * off,size_t bytes)450 xlog_write_adv_cnt(void **ptr, int *len, int *off, size_t bytes)
451 {
452 	*ptr += bytes;
453 	*len -= bytes;
454 	*off += bytes;
455 }
456 
457 void	xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
458 int
459 xlog_write(
460 	struct xlog		*log,
461 	struct xfs_log_vec	*log_vector,
462 	struct xlog_ticket	*tic,
463 	xfs_lsn_t		*start_lsn,
464 	struct xlog_in_core	**commit_iclog,
465 	uint			flags);
466 
467 /*
468  * When we crack an atomic LSN, we sample it first so that the value will not
469  * change while we are cracking it into the component values. This means we
470  * will always get consistent component values to work from. This should always
471  * be used to sample and crack LSNs that are stored and updated in atomic
472  * variables.
473  */
474 static inline void
xlog_crack_atomic_lsn(atomic64_t * lsn,uint * cycle,uint * block)475 xlog_crack_atomic_lsn(atomic64_t *lsn, uint *cycle, uint *block)
476 {
477 	xfs_lsn_t val = atomic64_read(lsn);
478 
479 	*cycle = CYCLE_LSN(val);
480 	*block = BLOCK_LSN(val);
481 }
482 
483 /*
484  * Calculate and assign a value to an atomic LSN variable from component pieces.
485  */
486 static inline void
xlog_assign_atomic_lsn(atomic64_t * lsn,uint cycle,uint block)487 xlog_assign_atomic_lsn(atomic64_t *lsn, uint cycle, uint block)
488 {
489 	atomic64_set(lsn, xlog_assign_lsn(cycle, block));
490 }
491 
492 /*
493  * When we crack the grant head, we sample it first so that the value will not
494  * change while we are cracking it into the component values. This means we
495  * will always get consistent component values to work from.
496  */
497 static inline void
xlog_crack_grant_head_val(int64_t val,int * cycle,int * space)498 xlog_crack_grant_head_val(int64_t val, int *cycle, int *space)
499 {
500 	*cycle = val >> 32;
501 	*space = val & 0xffffffff;
502 }
503 
504 static inline void
xlog_crack_grant_head(atomic64_t * head,int * cycle,int * space)505 xlog_crack_grant_head(atomic64_t *head, int *cycle, int *space)
506 {
507 	xlog_crack_grant_head_val(atomic64_read(head), cycle, space);
508 }
509 
510 static inline int64_t
xlog_assign_grant_head_val(int cycle,int space)511 xlog_assign_grant_head_val(int cycle, int space)
512 {
513 	return ((int64_t)cycle << 32) | space;
514 }
515 
516 static inline void
xlog_assign_grant_head(atomic64_t * head,int cycle,int space)517 xlog_assign_grant_head(atomic64_t *head, int cycle, int space)
518 {
519 	atomic64_set(head, xlog_assign_grant_head_val(cycle, space));
520 }
521 
522 /*
523  * Committed Item List interfaces
524  */
525 int	xlog_cil_init(struct xlog *log);
526 void	xlog_cil_init_post_recovery(struct xlog *log);
527 void	xlog_cil_destroy(struct xlog *log);
528 bool	xlog_cil_empty(struct xlog *log);
529 
530 /*
531  * CIL force routines
532  */
533 xfs_lsn_t
534 xlog_cil_force_lsn(
535 	struct xlog *log,
536 	xfs_lsn_t sequence);
537 
538 static inline void
xlog_cil_force(struct xlog * log)539 xlog_cil_force(struct xlog *log)
540 {
541 	xlog_cil_force_lsn(log, log->l_cilp->xc_current_sequence);
542 }
543 
544 /*
545  * Unmount record type is used as a pseudo transaction type for the ticket.
546  * It's value must be outside the range of XFS_TRANS_* values.
547  */
548 #define XLOG_UNMOUNT_REC_TYPE	(-1U)
549 
550 /*
551  * Wrapper function for waiting on a wait queue serialised against wakeups
552  * by a spinlock. This matches the semantics of all the wait queues used in the
553  * log code.
554  */
xlog_wait(wait_queue_head_t * wq,spinlock_t * lock)555 static inline void xlog_wait(wait_queue_head_t *wq, spinlock_t *lock)
556 {
557 	DECLARE_WAITQUEUE(wait, current);
558 
559 	add_wait_queue_exclusive(wq, &wait);
560 	__set_current_state(TASK_UNINTERRUPTIBLE);
561 	spin_unlock(lock);
562 	schedule();
563 	remove_wait_queue(wq, &wait);
564 }
565 
566 /*
567  * The LSN is valid so long as it is behind the current LSN. If it isn't, this
568  * means that the next log record that includes this metadata could have a
569  * smaller LSN. In turn, this means that the modification in the log would not
570  * replay.
571  */
572 static inline bool
xlog_valid_lsn(struct xlog * log,xfs_lsn_t lsn)573 xlog_valid_lsn(
574 	struct xlog	*log,
575 	xfs_lsn_t	lsn)
576 {
577 	int		cur_cycle;
578 	int		cur_block;
579 	bool		valid = true;
580 
581 	/*
582 	 * First, sample the current lsn without locking to avoid added
583 	 * contention from metadata I/O. The current cycle and block are updated
584 	 * (in xlog_state_switch_iclogs()) and read here in a particular order
585 	 * to avoid false negatives (e.g., thinking the metadata LSN is valid
586 	 * when it is not).
587 	 *
588 	 * The current block is always rewound before the cycle is bumped in
589 	 * xlog_state_switch_iclogs() to ensure the current LSN is never seen in
590 	 * a transiently forward state. Instead, we can see the LSN in a
591 	 * transiently behind state if we happen to race with a cycle wrap.
592 	 */
593 	cur_cycle = ACCESS_ONCE(log->l_curr_cycle);
594 	smp_rmb();
595 	cur_block = ACCESS_ONCE(log->l_curr_block);
596 
597 	if ((CYCLE_LSN(lsn) > cur_cycle) ||
598 	    (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block)) {
599 		/*
600 		 * If the metadata LSN appears invalid, it's possible the check
601 		 * above raced with a wrap to the next log cycle. Grab the lock
602 		 * to check for sure.
603 		 */
604 		spin_lock(&log->l_icloglock);
605 		cur_cycle = log->l_curr_cycle;
606 		cur_block = log->l_curr_block;
607 		spin_unlock(&log->l_icloglock);
608 
609 		if ((CYCLE_LSN(lsn) > cur_cycle) ||
610 		    (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block))
611 			valid = false;
612 	}
613 
614 	return valid;
615 }
616 
617 #endif	/* __XFS_LOG_PRIV_H__ */
618