/*
* Functions to sequence FLUSH and FUA writes.
*
* Copyright (C) 2011 Max Planck Institute for Gravitational Physics
* Copyright (C) 2011 Tejun Heo <tj@kernel.org>
*
* This file is released under the GPLv2.
*
* REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three
* optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
* properties and hardware capability.
*
* If a request doesn't have data, only REQ_FLUSH makes sense, which
* indicates a simple flush request. If there is data, REQ_FLUSH indicates
* that the device cache should be flushed before the data is executed, and
* REQ_FUA means that the data must be on non-volatile media on request
* completion.
*
* If the device doesn't have writeback cache, FLUSH and FUA don't make any
* difference. The requests are either completed immediately if there's no
* data or executed as normal requests otherwise.
*
* If the device has writeback cache and supports FUA, REQ_FLUSH is
* translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
*
* If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
* translated to PREFLUSH and REQ_FUA to POSTFLUSH.
*
* The actual execution of flush is double buffered. Whenever a request
* needs to execute PRE or POSTFLUSH, it queues at
* q->flush_queue[q->flush_pending_idx]. Once certain criteria are met, a
* flush is issued and the pending_idx is toggled. When the flush
* completes, all the requests which were pending are proceeded to the next
* step. This allows arbitrary merging of different types of FLUSH/FUA
* requests.
*
* Currently, the following conditions are used to determine when to issue
* flush.
*
* C1. At any given time, only one flush shall be in progress. This makes
* double buffering sufficient.
*
* C2. Flush is deferred if any request is executing DATA of its sequence.
* This avoids issuing separate POSTFLUSHes for requests which shared
* PREFLUSH.
*
* C3. The second condition is ignored if there is a request which has
* waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
* starvation in the unlikely case where there are continuous stream of
* FUA (without FLUSH) requests.
*
* For devices which support FUA, it isn't clear whether C2 (and thus C3)
* is beneficial.
*
* Note that a sequenced FLUSH/FUA request with DATA is completed twice.
* Once while executing DATA and again after the whole sequence is
* complete. The first completion updates the contained bio but doesn't
* finish it so that the bio submitter is notified only after the whole
* sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in
* req_bio_endio().
*
* The above peculiarity requires that each FLUSH/FUA request has only one
* bio attached to it, which is guaranteed as they aren't allowed to be
* merged in the usual way.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/gfp.h>
#include "blk.h"
/* FLUSH/FUA sequences */
enum {
REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
REQ_FSEQ_DONE = (1 << 3),
REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
REQ_FSEQ_POSTFLUSH,
/*
* If flush has been pending longer than the following timeout,
* it's issued even if flush_data requests are still in flight.
*/
FLUSH_PENDING_TIMEOUT = 5 * HZ,
};
static bool blk_kick_flush(struct request_queue *q);
static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
{
unsigned int policy = 0;
if (blk_rq_sectors(rq))
policy |= REQ_FSEQ_DATA;
if (fflags & REQ_FLUSH) {
if (rq->cmd_flags & REQ_FLUSH)
policy |= REQ_FSEQ_PREFLUSH;
if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
policy |= REQ_FSEQ_POSTFLUSH;
}
return policy;
}
static unsigned int blk_flush_cur_seq(struct request *rq)
{
return 1 << ffz(rq->flush.seq);
}
static void blk_flush_restore_request(struct request *rq)
{
/*
* After flush data completion, @rq->bio is %NULL but we need to
* complete the bio again. @rq->biotail is guaranteed to equal the
* original @rq->bio. Restore it.
*/
rq->bio = rq->biotail;
/* make @rq a normal request */
rq->cmd_flags &= ~REQ_FLUSH_SEQ;
rq->end_io = rq->flush.saved_end_io;
}
/**
* blk_flush_complete_seq - complete flush sequence
* @rq: FLUSH/FUA request being sequenced
* @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
* @error: whether an error occurred
*
* @rq just completed @seq part of its flush sequence, record the
* completion and trigger the next step.
*
* CONTEXT:
* spin_lock_irq(q->queue_lock)
*
* RETURNS:
* %true if requests were added to the dispatch queue, %false otherwise.
*/
static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
int error)
{
struct request_queue *q = rq->q;
struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
bool queued = false;
BUG_ON(rq->flush.seq & seq);
rq->flush.seq |= seq;
if (likely(!error))
seq = blk_flush_cur_seq(rq);
else
seq = REQ_FSEQ_DONE;
switch (seq) {
case REQ_FSEQ_PREFLUSH:
case REQ_FSEQ_POSTFLUSH:
/* queue for flush */
if (list_empty(pending))
q->flush_pending_since = jiffies;
list_move_tail(&rq->flush.list, pending);
break;
case REQ_FSEQ_DATA:
list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
list_add(&rq->queuelist, &q->queue_head);
queued = true;
break;
case REQ_FSEQ_DONE:
/*
* @rq was previously adjusted by blk_flush_issue() for
* flush sequencing and may already have gone through the
* flush data request completion path. Restore @rq for
* normal completion and end it.
*/
BUG_ON(!list_empty(&rq->queuelist));
list_del_init(&rq->flush.list);
blk_flush_restore_request(rq);
__blk_end_request_all(rq, error);
break;
default:
BUG();
}
return blk_kick_flush(q) | queued;
}
static void flush_end_io(struct request *flush_rq, int error)
{
struct request_queue *q = flush_rq->q;
struct list_head *running = &q->flush_queue[q->flush_running_idx];
bool queued = false;
struct request *rq, *n;
BUG_ON(q->flush_pending_idx == q->flush_running_idx);
/* account completion of the flush request */
q->flush_running_idx ^= 1;
elv_completed_request(q, flush_rq);
/* and push the waiting requests to the next stage */
list_for_each_entry_safe(rq, n, running, flush.list) {
unsigned int seq = blk_flush_cur_seq(rq);
BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
queued |= blk_flush_complete_seq(rq, seq, error);
}
/*
* Kick the queue to avoid stall for two cases:
* 1. Moving a request silently to empty queue_head may stall the
* queue.
* 2. When flush request is running in non-queueable queue, the
* queue is hold. Restart the queue after flush request is finished
* to avoid stall.
* This function is called from request completion path and calling
* directly into request_fn may confuse the driver. Always use
* kblockd.
*/
if (queued || q->flush_queue_delayed)
blk_run_queue_async(q);
q->flush_queue_delayed = 0;
}
/**
* blk_kick_flush - consider issuing flush request
* @q: request_queue being kicked
*
* Flush related states of @q have changed, consider issuing flush request.
* Please read the comment at the top of this file for more info.
*
* CONTEXT:
* spin_lock_irq(q->queue_lock)
*
* RETURNS:
* %true if flush was issued, %false otherwise.
*/
static bool blk_kick_flush(struct request_queue *q)
{
struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
struct request *first_rq =
list_first_entry(pending, struct request, flush.list);
/* C1 described at the top of this file */
if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
return false;
/* C2 and C3 */
if (!list_empty(&q->flush_data_in_flight) &&
time_before(jiffies,
q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
return false;
/*
* Issue flush and toggle pending_idx. This makes pending_idx
* different from running_idx, which means flush is in flight.
*/
blk_rq_init(q, &q->flush_rq);
q->flush_rq.cmd_type = REQ_TYPE_FS;
q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
q->flush_rq.rq_disk = first_rq->rq_disk;
q->flush_rq.end_io = flush_end_io;
q->flush_pending_idx ^= 1;
list_add_tail(&q->flush_rq.queuelist, &q->queue_head);
return true;
}
static void flush_data_end_io(struct request *rq, int error)
{
struct request_queue *q = rq->q;
/*
* After populating an empty queue, kick it to avoid stall. Read
* the comment in flush_end_io().
*/
if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
blk_run_queue_async(q);
}
/**
* blk_insert_flush - insert a new FLUSH/FUA request
* @rq: request to insert
*
* To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
* @rq is being submitted. Analyze what needs to be done and put it on the
* right queue.
*
* CONTEXT:
* spin_lock_irq(q->queue_lock)
*/
void blk_insert_flush(struct request *rq)
{
struct request_queue *q = rq->q;
unsigned int fflags = q->flush_flags; /* may change, cache */
unsigned int policy = blk_flush_policy(fflags, rq);
/*
* @policy now records what operations need to be done. Adjust
* REQ_FLUSH and FUA for the driver.
*/
rq->cmd_flags &= ~REQ_FLUSH;
if (!(fflags & REQ_FUA))
rq->cmd_flags &= ~REQ_FUA;
/*
* An empty flush handed down from a stacking driver may
* translate into nothing if the underlying device does not
* advertise a write-back cache. In this case, simply
* complete the request.
*/
if (!policy) {
__blk_end_bidi_request(rq, 0, 0, 0);
return;
}
BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
/*
* If there's data but flush is not necessary, the request can be
* processed directly without going through flush machinery. Queue
* for normal execution.
*/
if ((policy & REQ_FSEQ_DATA) &&
!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
list_add_tail(&rq->queuelist, &q->queue_head);
return;
}
/*
* @rq should go through flush machinery. Mark it part of flush
* sequence and submit for further processing.
*/
memset(&rq->flush, 0, sizeof(rq->flush));
INIT_LIST_HEAD(&rq->flush.list);
rq->cmd_flags |= REQ_FLUSH_SEQ;
rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
rq->end_io = flush_data_end_io;
blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
}
/**
* blk_abort_flushes - @q is being aborted, abort flush requests
* @q: request_queue being aborted
*
* To be called from elv_abort_queue(). @q is being aborted. Prepare all
* FLUSH/FUA requests for abortion.
*
* CONTEXT:
* spin_lock_irq(q->queue_lock)
*/
void blk_abort_flushes(struct request_queue *q)
{
struct request *rq, *n;
int i;
/*
* Requests in flight for data are already owned by the dispatch
* queue or the device driver. Just restore for normal completion.
*/
list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {
list_del_init(&rq->flush.list);
blk_flush_restore_request(rq);
}
/*
* We need to give away requests on flush queues. Restore for
* normal completion and put them on the dispatch queue.
*/
for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {
list_for_each_entry_safe(rq, n, &q->flush_queue[i],
flush.list) {
list_del_init(&rq->flush.list);
blk_flush_restore_request(rq);
list_add_tail(&rq->queuelist, &q->queue_head);
}
}
}
static void bio_end_flush(struct bio *bio, int err)
{
if (err)
clear_bit(BIO_UPTODATE, &bio->bi_flags);
if (bio->bi_private)
complete(bio->bi_private);
bio_put(bio);
}
/**
* blkdev_issue_flush - queue a flush
* @bdev: blockdev to issue flush for
* @gfp_mask: memory allocation flags (for bio_alloc)
* @error_sector: error sector
*
* Description:
* Issue a flush for the block device in question. Caller can supply
* room for storing the error offset in case of a flush error, if they
* wish to. If WAIT flag is not passed then caller may check only what
* request was pushed in some internal queue for later handling.
*/
int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
sector_t *error_sector)
{
DECLARE_COMPLETION_ONSTACK(wait);
struct request_queue *q;
struct bio *bio;
int ret = 0;
if (bdev->bd_disk == NULL)
return -ENXIO;
q = bdev_get_queue(bdev);
if (!q)
return -ENXIO;
/*
* some block devices may not have their queue correctly set up here
* (e.g. loop device without a backing file) and so issuing a flush
* here will panic. Ensure there is a request function before issuing
* the flush.
*/
if (!q->make_request_fn)
return -ENXIO;
bio = bio_alloc(gfp_mask, 0);
bio->bi_end_io = bio_end_flush;
bio->bi_bdev = bdev;
bio->bi_private = &wait;
bio_get(bio);
submit_bio(WRITE_FLUSH, bio);
wait_for_completion(&wait);
/*
* The driver must store the error location in ->bi_sector, if
* it supports it. For non-stacked drivers, this should be
* copied from blk_rq_pos(rq).
*/
if (error_sector)
*error_sector = bio->bi_sector;
if (!bio_flagged(bio, BIO_UPTODATE))
ret = -EIO;
bio_put(bio);
return ret;
}
EXPORT_SYMBOL(blkdev_issue_flush);
