Root/block/blk-flush.c

1/*
2 * Functions to sequence FLUSH and FUA writes.
3 *
4 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
5 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
6 *
7 * This file is released under the GPLv2.
8 *
9 * REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three
10 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
11 * properties and hardware capability.
12 *
13 * If a request doesn't have data, only REQ_FLUSH makes sense, which
14 * indicates a simple flush request. If there is data, REQ_FLUSH indicates
15 * that the device cache should be flushed before the data is executed, and
16 * REQ_FUA means that the data must be on non-volatile media on request
17 * completion.
18 *
19 * If the device doesn't have writeback cache, FLUSH and FUA don't make any
20 * difference. The requests are either completed immediately if there's no
21 * data or executed as normal requests otherwise.
22 *
23 * If the device has writeback cache and supports FUA, REQ_FLUSH is
24 * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
25 *
26 * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
27 * translated to PREFLUSH and REQ_FUA to POSTFLUSH.
28 *
29 * The actual execution of flush is double buffered. Whenever a request
30 * needs to execute PRE or POSTFLUSH, it queues at
31 * q->flush_queue[q->flush_pending_idx]. Once certain criteria are met, a
32 * flush is issued and the pending_idx is toggled. When the flush
33 * completes, all the requests which were pending are proceeded to the next
34 * step. This allows arbitrary merging of different types of FLUSH/FUA
35 * requests.
36 *
37 * Currently, the following conditions are used to determine when to issue
38 * flush.
39 *
40 * C1. At any given time, only one flush shall be in progress. This makes
41 * double buffering sufficient.
42 *
43 * C2. Flush is deferred if any request is executing DATA of its sequence.
44 * This avoids issuing separate POSTFLUSHes for requests which shared
45 * PREFLUSH.
46 *
47 * C3. The second condition is ignored if there is a request which has
48 * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
49 * starvation in the unlikely case where there are continuous stream of
50 * FUA (without FLUSH) requests.
51 *
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
53 * is beneficial.
54 *
55 * Note that a sequenced FLUSH/FUA request with DATA is completed twice.
56 * Once while executing DATA and again after the whole sequence is
57 * complete. The first completion updates the contained bio but doesn't
58 * finish it so that the bio submitter is notified only after the whole
59 * sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in
60 * req_bio_endio().
61 *
62 * The above peculiarity requires that each FLUSH/FUA request has only one
63 * bio attached to it, which is guaranteed as they aren't allowed to be
64 * merged in the usual way.
65 */
66
67#include <linux/kernel.h>
68#include <linux/module.h>
69#include <linux/bio.h>
70#include <linux/blkdev.h>
71#include <linux/gfp.h>
72
73#include "blk.h"
74
75/* FLUSH/FUA sequences */
76enum {
77    REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
78    REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
79    REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
80    REQ_FSEQ_DONE = (1 << 3),
81
82    REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
83                  REQ_FSEQ_POSTFLUSH,
84
85    /*
86     * If flush has been pending longer than the following timeout,
87     * it's issued even if flush_data requests are still in flight.
88     */
89    FLUSH_PENDING_TIMEOUT = 5 * HZ,
90};
91
92static bool blk_kick_flush(struct request_queue *q);
93
94static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
95{
96    unsigned int policy = 0;
97
98    if (blk_rq_sectors(rq))
99        policy |= REQ_FSEQ_DATA;
100
101    if (fflags & REQ_FLUSH) {
102        if (rq->cmd_flags & REQ_FLUSH)
103            policy |= REQ_FSEQ_PREFLUSH;
104        if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
105            policy |= REQ_FSEQ_POSTFLUSH;
106    }
107    return policy;
108}
109
110static unsigned int blk_flush_cur_seq(struct request *rq)
111{
112    return 1 << ffz(rq->flush.seq);
113}
114
115static void blk_flush_restore_request(struct request *rq)
116{
117    /*
118     * After flush data completion, @rq->bio is %NULL but we need to
119     * complete the bio again. @rq->biotail is guaranteed to equal the
120     * original @rq->bio. Restore it.
121     */
122    rq->bio = rq->biotail;
123
124    /* make @rq a normal request */
125    rq->cmd_flags &= ~REQ_FLUSH_SEQ;
126    rq->end_io = rq->flush.saved_end_io;
127}
128
129/**
130 * blk_flush_complete_seq - complete flush sequence
131 * @rq: FLUSH/FUA request being sequenced
132 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
133 * @error: whether an error occurred
134 *
135 * @rq just completed @seq part of its flush sequence, record the
136 * completion and trigger the next step.
137 *
138 * CONTEXT:
139 * spin_lock_irq(q->queue_lock)
140 *
141 * RETURNS:
142 * %true if requests were added to the dispatch queue, %false otherwise.
143 */
144static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
145                   int error)
146{
147    struct request_queue *q = rq->q;
148    struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
149    bool queued = false;
150
151    BUG_ON(rq->flush.seq & seq);
152    rq->flush.seq |= seq;
153
154    if (likely(!error))
155        seq = blk_flush_cur_seq(rq);
156    else
157        seq = REQ_FSEQ_DONE;
158
159    switch (seq) {
160    case REQ_FSEQ_PREFLUSH:
161    case REQ_FSEQ_POSTFLUSH:
162        /* queue for flush */
163        if (list_empty(pending))
164            q->flush_pending_since = jiffies;
165        list_move_tail(&rq->flush.list, pending);
166        break;
167
168    case REQ_FSEQ_DATA:
169        list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
170        list_add(&rq->queuelist, &q->queue_head);
171        queued = true;
172        break;
173
174    case REQ_FSEQ_DONE:
175        /*
176         * @rq was previously adjusted by blk_flush_issue() for
177         * flush sequencing and may already have gone through the
178         * flush data request completion path. Restore @rq for
179         * normal completion and end it.
180         */
181        BUG_ON(!list_empty(&rq->queuelist));
182        list_del_init(&rq->flush.list);
183        blk_flush_restore_request(rq);
184        __blk_end_request_all(rq, error);
185        break;
186
187    default:
188        BUG();
189    }
190
191    return blk_kick_flush(q) | queued;
192}
193
194static void flush_end_io(struct request *flush_rq, int error)
195{
196    struct request_queue *q = flush_rq->q;
197    struct list_head *running = &q->flush_queue[q->flush_running_idx];
198    bool queued = false;
199    struct request *rq, *n;
200
201    BUG_ON(q->flush_pending_idx == q->flush_running_idx);
202
203    /* account completion of the flush request */
204    q->flush_running_idx ^= 1;
205    elv_completed_request(q, flush_rq);
206
207    /* and push the waiting requests to the next stage */
208    list_for_each_entry_safe(rq, n, running, flush.list) {
209        unsigned int seq = blk_flush_cur_seq(rq);
210
211        BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
212        queued |= blk_flush_complete_seq(rq, seq, error);
213    }
214
215    /*
216     * Kick the queue to avoid stall for two cases:
217     * 1. Moving a request silently to empty queue_head may stall the
218     * queue.
219     * 2. When flush request is running in non-queueable queue, the
220     * queue is hold. Restart the queue after flush request is finished
221     * to avoid stall.
222     * This function is called from request completion path and calling
223     * directly into request_fn may confuse the driver. Always use
224     * kblockd.
225     */
226    if (queued || q->flush_queue_delayed)
227        blk_run_queue_async(q);
228    q->flush_queue_delayed = 0;
229}
230
231/**
232 * blk_kick_flush - consider issuing flush request
233 * @q: request_queue being kicked
234 *
235 * Flush related states of @q have changed, consider issuing flush request.
236 * Please read the comment at the top of this file for more info.
237 *
238 * CONTEXT:
239 * spin_lock_irq(q->queue_lock)
240 *
241 * RETURNS:
242 * %true if flush was issued, %false otherwise.
243 */
244static bool blk_kick_flush(struct request_queue *q)
245{
246    struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
247    struct request *first_rq =
248        list_first_entry(pending, struct request, flush.list);
249
250    /* C1 described at the top of this file */
251    if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
252        return false;
253
254    /* C2 and C3 */
255    if (!list_empty(&q->flush_data_in_flight) &&
256        time_before(jiffies,
257            q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
258        return false;
259
260    /*
261     * Issue flush and toggle pending_idx. This makes pending_idx
262     * different from running_idx, which means flush is in flight.
263     */
264    blk_rq_init(q, &q->flush_rq);
265    q->flush_rq.cmd_type = REQ_TYPE_FS;
266    q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
267    q->flush_rq.rq_disk = first_rq->rq_disk;
268    q->flush_rq.end_io = flush_end_io;
269
270    q->flush_pending_idx ^= 1;
271    list_add_tail(&q->flush_rq.queuelist, &q->queue_head);
272    return true;
273}
274
275static void flush_data_end_io(struct request *rq, int error)
276{
277    struct request_queue *q = rq->q;
278
279    /*
280     * After populating an empty queue, kick it to avoid stall. Read
281     * the comment in flush_end_io().
282     */
283    if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
284        blk_run_queue_async(q);
285}
286
287/**
288 * blk_insert_flush - insert a new FLUSH/FUA request
289 * @rq: request to insert
290 *
291 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
292 * @rq is being submitted. Analyze what needs to be done and put it on the
293 * right queue.
294 *
295 * CONTEXT:
296 * spin_lock_irq(q->queue_lock)
297 */
298void blk_insert_flush(struct request *rq)
299{
300    struct request_queue *q = rq->q;
301    unsigned int fflags = q->flush_flags; /* may change, cache */
302    unsigned int policy = blk_flush_policy(fflags, rq);
303
304    /*
305     * @policy now records what operations need to be done. Adjust
306     * REQ_FLUSH and FUA for the driver.
307     */
308    rq->cmd_flags &= ~REQ_FLUSH;
309    if (!(fflags & REQ_FUA))
310        rq->cmd_flags &= ~REQ_FUA;
311
312    /*
313     * An empty flush handed down from a stacking driver may
314     * translate into nothing if the underlying device does not
315     * advertise a write-back cache. In this case, simply
316     * complete the request.
317     */
318    if (!policy) {
319        __blk_end_bidi_request(rq, 0, 0, 0);
320        return;
321    }
322
323    BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
324
325    /*
326     * If there's data but flush is not necessary, the request can be
327     * processed directly without going through flush machinery. Queue
328     * for normal execution.
329     */
330    if ((policy & REQ_FSEQ_DATA) &&
331        !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
332        list_add_tail(&rq->queuelist, &q->queue_head);
333        return;
334    }
335
336    /*
337     * @rq should go through flush machinery. Mark it part of flush
338     * sequence and submit for further processing.
339     */
340    memset(&rq->flush, 0, sizeof(rq->flush));
341    INIT_LIST_HEAD(&rq->flush.list);
342    rq->cmd_flags |= REQ_FLUSH_SEQ;
343    rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
344    rq->end_io = flush_data_end_io;
345
346    blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
347}
348
349/**
350 * blk_abort_flushes - @q is being aborted, abort flush requests
351 * @q: request_queue being aborted
352 *
353 * To be called from elv_abort_queue(). @q is being aborted. Prepare all
354 * FLUSH/FUA requests for abortion.
355 *
356 * CONTEXT:
357 * spin_lock_irq(q->queue_lock)
358 */
359void blk_abort_flushes(struct request_queue *q)
360{
361    struct request *rq, *n;
362    int i;
363
364    /*
365     * Requests in flight for data are already owned by the dispatch
366     * queue or the device driver. Just restore for normal completion.
367     */
368    list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {
369        list_del_init(&rq->flush.list);
370        blk_flush_restore_request(rq);
371    }
372
373    /*
374     * We need to give away requests on flush queues. Restore for
375     * normal completion and put them on the dispatch queue.
376     */
377    for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {
378        list_for_each_entry_safe(rq, n, &q->flush_queue[i],
379                     flush.list) {
380            list_del_init(&rq->flush.list);
381            blk_flush_restore_request(rq);
382            list_add_tail(&rq->queuelist, &q->queue_head);
383        }
384    }
385}
386
387static void bio_end_flush(struct bio *bio, int err)
388{
389    if (err)
390        clear_bit(BIO_UPTODATE, &bio->bi_flags);
391    if (bio->bi_private)
392        complete(bio->bi_private);
393    bio_put(bio);
394}
395
396/**
397 * blkdev_issue_flush - queue a flush
398 * @bdev: blockdev to issue flush for
399 * @gfp_mask: memory allocation flags (for bio_alloc)
400 * @error_sector: error sector
401 *
402 * Description:
403 * Issue a flush for the block device in question. Caller can supply
404 * room for storing the error offset in case of a flush error, if they
405 * wish to. If WAIT flag is not passed then caller may check only what
406 * request was pushed in some internal queue for later handling.
407 */
408int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
409        sector_t *error_sector)
410{
411    DECLARE_COMPLETION_ONSTACK(wait);
412    struct request_queue *q;
413    struct bio *bio;
414    int ret = 0;
415
416    if (bdev->bd_disk == NULL)
417        return -ENXIO;
418
419    q = bdev_get_queue(bdev);
420    if (!q)
421        return -ENXIO;
422
423    /*
424     * some block devices may not have their queue correctly set up here
425     * (e.g. loop device without a backing file) and so issuing a flush
426     * here will panic. Ensure there is a request function before issuing
427     * the flush.
428     */
429    if (!q->make_request_fn)
430        return -ENXIO;
431
432    bio = bio_alloc(gfp_mask, 0);
433    bio->bi_end_io = bio_end_flush;
434    bio->bi_bdev = bdev;
435    bio->bi_private = &wait;
436
437    bio_get(bio);
438    submit_bio(WRITE_FLUSH, bio);
439    wait_for_completion_io(&wait);
440
441    /*
442     * The driver must store the error location in ->bi_sector, if
443     * it supports it. For non-stacked drivers, this should be
444     * copied from blk_rq_pos(rq).
445     */
446    if (error_sector)
447        *error_sector = bio->bi_sector;
448
449    if (!bio_flagged(bio, BIO_UPTODATE))
450        ret = -EIO;
451
452    bio_put(bio);
453    return ret;
454}
455EXPORT_SYMBOL(blkdev_issue_flush);
456

Archive Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive