![Tejun Heo](/assets/img/avatar_default.png)
blk-flush decomposes a flush into sequence of multiple requests. On completion of a request, the next one is queued; however, block layer must not implicitly call into q->request_fn() directly from completion path. This makes the queue behave unexpectedly when seen from the drivers and violates the assumption that q->request_fn() is called with process context + queue_lock. This patch makes blk-flush the following two changes to make sure q->request_fn() is not called directly from request completion path. - blk_flush_complete_seq_end_io() now asks __blk_run_queue() to always use kblockd instead of calling directly into q->request_fn(). - queue_next_fseq() uses ELEVATOR_INSERT_REQUEUE instead of ELEVATOR_INSERT_FRONT so that elv_insert() doesn't try to unplug the request queue directly. Reported by Jan in the following threads. http://thread.gmane.org/gmane.linux.ide/48778 http://thread.gmane.org/gmane.linux.ide/48786 stable: applicable to v2.6.37. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Jan Beulich <JBeulich@novell.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: stable@kernel.org Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
265 lines
6.8 KiB
C
265 lines
6.8 KiB
C
/*
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* Functions to sequence FLUSH and FUA writes.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/bio.h>
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#include <linux/blkdev.h>
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#include <linux/gfp.h>
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#include "blk.h"
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/* FLUSH/FUA sequences */
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enum {
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QUEUE_FSEQ_STARTED = (1 << 0), /* flushing in progress */
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QUEUE_FSEQ_PREFLUSH = (1 << 1), /* pre-flushing in progress */
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QUEUE_FSEQ_DATA = (1 << 2), /* data write in progress */
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QUEUE_FSEQ_POSTFLUSH = (1 << 3), /* post-flushing in progress */
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QUEUE_FSEQ_DONE = (1 << 4),
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};
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static struct request *queue_next_fseq(struct request_queue *q);
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unsigned blk_flush_cur_seq(struct request_queue *q)
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{
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if (!q->flush_seq)
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return 0;
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return 1 << ffz(q->flush_seq);
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}
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static struct request *blk_flush_complete_seq(struct request_queue *q,
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unsigned seq, int error)
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{
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struct request *next_rq = NULL;
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if (error && !q->flush_err)
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q->flush_err = error;
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BUG_ON(q->flush_seq & seq);
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q->flush_seq |= seq;
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if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
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/* not complete yet, queue the next flush sequence */
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next_rq = queue_next_fseq(q);
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} else {
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/* complete this flush request */
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__blk_end_request_all(q->orig_flush_rq, q->flush_err);
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q->orig_flush_rq = NULL;
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q->flush_seq = 0;
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/* dispatch the next flush if there's one */
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if (!list_empty(&q->pending_flushes)) {
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next_rq = list_entry_rq(q->pending_flushes.next);
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list_move(&next_rq->queuelist, &q->queue_head);
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}
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}
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return next_rq;
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}
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static void blk_flush_complete_seq_end_io(struct request_queue *q,
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unsigned seq, int error)
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{
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bool was_empty = elv_queue_empty(q);
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struct request *next_rq;
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next_rq = blk_flush_complete_seq(q, seq, error);
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/*
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* Moving a request silently to empty queue_head may stall the
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* queue. Kick the queue in those cases. This function is called
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* from request completion path and calling directly into
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* request_fn may confuse the driver. Always use kblockd.
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*/
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if (was_empty && next_rq)
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__blk_run_queue(q, true);
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}
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static void pre_flush_end_io(struct request *rq, int error)
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{
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elv_completed_request(rq->q, rq);
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blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
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}
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static void flush_data_end_io(struct request *rq, int error)
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{
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elv_completed_request(rq->q, rq);
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blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
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}
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static void post_flush_end_io(struct request *rq, int error)
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{
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elv_completed_request(rq->q, rq);
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blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
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}
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static void init_flush_request(struct request *rq, struct gendisk *disk)
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{
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rq->cmd_type = REQ_TYPE_FS;
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rq->cmd_flags = WRITE_FLUSH;
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rq->rq_disk = disk;
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}
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static struct request *queue_next_fseq(struct request_queue *q)
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{
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struct request *orig_rq = q->orig_flush_rq;
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struct request *rq = &q->flush_rq;
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blk_rq_init(q, rq);
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switch (blk_flush_cur_seq(q)) {
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case QUEUE_FSEQ_PREFLUSH:
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init_flush_request(rq, orig_rq->rq_disk);
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rq->end_io = pre_flush_end_io;
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break;
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case QUEUE_FSEQ_DATA:
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init_request_from_bio(rq, orig_rq->bio);
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/*
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* orig_rq->rq_disk may be different from
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* bio->bi_bdev->bd_disk if orig_rq got here through
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* remapping drivers. Make sure rq->rq_disk points
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* to the same one as orig_rq.
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*/
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rq->rq_disk = orig_rq->rq_disk;
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rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
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rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
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rq->end_io = flush_data_end_io;
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break;
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case QUEUE_FSEQ_POSTFLUSH:
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init_flush_request(rq, orig_rq->rq_disk);
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rq->end_io = post_flush_end_io;
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break;
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default:
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BUG();
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}
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elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
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return rq;
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}
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struct request *blk_do_flush(struct request_queue *q, struct request *rq)
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{
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unsigned int fflags = q->flush_flags; /* may change, cache it */
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bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
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bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
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bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
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unsigned skip = 0;
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/*
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* Special case. If there's data but flush is not necessary,
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* the request can be issued directly.
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*
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* Flush w/o data should be able to be issued directly too but
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* currently some drivers assume that rq->bio contains
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* non-zero data if it isn't NULL and empty FLUSH requests
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* getting here usually have bio's without data.
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*/
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if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
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rq->cmd_flags &= ~REQ_FLUSH;
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if (!has_fua)
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rq->cmd_flags &= ~REQ_FUA;
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return rq;
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}
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/*
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* Sequenced flushes can't be processed in parallel. If
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* another one is already in progress, queue for later
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* processing.
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*/
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if (q->flush_seq) {
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list_move_tail(&rq->queuelist, &q->pending_flushes);
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return NULL;
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}
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/*
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* Start a new flush sequence
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*/
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q->flush_err = 0;
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q->flush_seq |= QUEUE_FSEQ_STARTED;
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/* adjust FLUSH/FUA of the original request and stash it away */
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rq->cmd_flags &= ~REQ_FLUSH;
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if (!has_fua)
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rq->cmd_flags &= ~REQ_FUA;
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blk_dequeue_request(rq);
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q->orig_flush_rq = rq;
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/* skip unneded sequences and return the first one */
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if (!do_preflush)
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skip |= QUEUE_FSEQ_PREFLUSH;
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if (!blk_rq_sectors(rq))
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skip |= QUEUE_FSEQ_DATA;
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if (!do_postflush)
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skip |= QUEUE_FSEQ_POSTFLUSH;
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return blk_flush_complete_seq(q, skip, 0);
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}
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static void bio_end_flush(struct bio *bio, int err)
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{
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if (err)
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clear_bit(BIO_UPTODATE, &bio->bi_flags);
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if (bio->bi_private)
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complete(bio->bi_private);
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bio_put(bio);
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}
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/**
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* blkdev_issue_flush - queue a flush
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* @bdev: blockdev to issue flush for
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* @gfp_mask: memory allocation flags (for bio_alloc)
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* @error_sector: error sector
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*
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* Description:
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* Issue a flush for the block device in question. Caller can supply
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* room for storing the error offset in case of a flush error, if they
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* wish to. If WAIT flag is not passed then caller may check only what
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* request was pushed in some internal queue for later handling.
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*/
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int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
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sector_t *error_sector)
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{
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DECLARE_COMPLETION_ONSTACK(wait);
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struct request_queue *q;
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struct bio *bio;
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int ret = 0;
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if (bdev->bd_disk == NULL)
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return -ENXIO;
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q = bdev_get_queue(bdev);
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if (!q)
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return -ENXIO;
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/*
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* some block devices may not have their queue correctly set up here
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* (e.g. loop device without a backing file) and so issuing a flush
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* here will panic. Ensure there is a request function before issuing
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* the flush.
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*/
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if (!q->make_request_fn)
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return -ENXIO;
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bio = bio_alloc(gfp_mask, 0);
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bio->bi_end_io = bio_end_flush;
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bio->bi_bdev = bdev;
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bio->bi_private = &wait;
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bio_get(bio);
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submit_bio(WRITE_FLUSH, bio);
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wait_for_completion(&wait);
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/*
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* The driver must store the error location in ->bi_sector, if
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* it supports it. For non-stacked drivers, this should be
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* copied from blk_rq_pos(rq).
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*/
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if (error_sector)
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*error_sector = bio->bi_sector;
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if (!bio_flagged(bio, BIO_UPTODATE))
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ret = -EIO;
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bio_put(bio);
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return ret;
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}
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EXPORT_SYMBOL(blkdev_issue_flush);
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