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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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e67b77c791
A dm-multipath user reported[1] a problem when trying to boot
a kernel with commit 4853abaae7
(block: fix flush machinery for stacking drivers with differring
flush flags) applied. It turns out that an empty flush request
can be sent into blk_insert_flush. When the BUG_ON was fixed
to allow for this, I/O on the underlying device would stall. The
reason is that blk_insert_cloned_request does not kick the queue.
In the aforementioned commit, I had added a special case to
kick the queue if data was sent down but the queue flags did
not require a flush. A better solution is to push the queue
kick up into blk_insert_cloned_request.
This patch, along with a follow-on which fixes the BUG_ON, fixes
the issue reported.
[1] http://www.redhat.com/archives/dm-devel/2011-September/msg00154.html
Reported-by: Christophe Saout <christophe@saout.de>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Stable note: 3.1
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
456 lines
13 KiB
C
456 lines
13 KiB
C
/*
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* Functions to sequence FLUSH and FUA writes.
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*
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* Copyright (C) 2011 Max Planck Institute for Gravitational Physics
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* Copyright (C) 2011 Tejun Heo <tj@kernel.org>
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*
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* This file is released under the GPLv2.
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*
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* REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three
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* optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
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* properties and hardware capability.
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*
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* If a request doesn't have data, only REQ_FLUSH makes sense, which
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* indicates a simple flush request. If there is data, REQ_FLUSH indicates
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* that the device cache should be flushed before the data is executed, and
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* REQ_FUA means that the data must be on non-volatile media on request
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* completion.
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*
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* If the device doesn't have writeback cache, FLUSH and FUA don't make any
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* difference. The requests are either completed immediately if there's no
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* data or executed as normal requests otherwise.
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*
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* If the device has writeback cache and supports FUA, REQ_FLUSH is
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* translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
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*
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* If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
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* translated to PREFLUSH and REQ_FUA to POSTFLUSH.
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*
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* The actual execution of flush is double buffered. Whenever a request
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* needs to execute PRE or POSTFLUSH, it queues at
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* q->flush_queue[q->flush_pending_idx]. Once certain criteria are met, a
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* flush is issued and the pending_idx is toggled. When the flush
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* completes, all the requests which were pending are proceeded to the next
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* step. This allows arbitrary merging of different types of FLUSH/FUA
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* requests.
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*
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* Currently, the following conditions are used to determine when to issue
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* flush.
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*
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* C1. At any given time, only one flush shall be in progress. This makes
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* double buffering sufficient.
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*
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* C2. Flush is deferred if any request is executing DATA of its sequence.
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* This avoids issuing separate POSTFLUSHes for requests which shared
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* PREFLUSH.
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*
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* C3. The second condition is ignored if there is a request which has
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* waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
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* starvation in the unlikely case where there are continuous stream of
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* FUA (without FLUSH) requests.
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*
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* For devices which support FUA, it isn't clear whether C2 (and thus C3)
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* is beneficial.
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*
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* Note that a sequenced FLUSH/FUA request with DATA is completed twice.
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* Once while executing DATA and again after the whole sequence is
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* complete. The first completion updates the contained bio but doesn't
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* finish it so that the bio submitter is notified only after the whole
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* sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in
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* req_bio_endio().
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*
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* The above peculiarity requires that each FLUSH/FUA request has only one
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* bio attached to it, which is guaranteed as they aren't allowed to be
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* merged in the usual way.
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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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REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
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REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
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REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
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REQ_FSEQ_DONE = (1 << 3),
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REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
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REQ_FSEQ_POSTFLUSH,
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/*
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* If flush has been pending longer than the following timeout,
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* it's issued even if flush_data requests are still in flight.
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*/
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FLUSH_PENDING_TIMEOUT = 5 * HZ,
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};
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static bool blk_kick_flush(struct request_queue *q);
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static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
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{
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unsigned int policy = 0;
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if (blk_rq_sectors(rq))
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policy |= REQ_FSEQ_DATA;
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if (fflags & REQ_FLUSH) {
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if (rq->cmd_flags & REQ_FLUSH)
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policy |= REQ_FSEQ_PREFLUSH;
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if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
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policy |= REQ_FSEQ_POSTFLUSH;
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}
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return policy;
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}
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static unsigned int blk_flush_cur_seq(struct request *rq)
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{
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return 1 << ffz(rq->flush.seq);
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}
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static void blk_flush_restore_request(struct request *rq)
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{
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/*
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* After flush data completion, @rq->bio is %NULL but we need to
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* complete the bio again. @rq->biotail is guaranteed to equal the
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* original @rq->bio. Restore it.
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*/
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rq->bio = rq->biotail;
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/* make @rq a normal request */
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rq->cmd_flags &= ~REQ_FLUSH_SEQ;
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rq->end_io = rq->flush.saved_end_io;
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}
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/**
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* blk_flush_complete_seq - complete flush sequence
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* @rq: FLUSH/FUA request being sequenced
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* @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
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* @error: whether an error occurred
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*
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* @rq just completed @seq part of its flush sequence, record the
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* completion and trigger the next step.
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*
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* CONTEXT:
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* spin_lock_irq(q->queue_lock)
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*
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* RETURNS:
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* %true if requests were added to the dispatch queue, %false otherwise.
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*/
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static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
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int error)
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{
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struct request_queue *q = rq->q;
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struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
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bool queued = false;
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BUG_ON(rq->flush.seq & seq);
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rq->flush.seq |= seq;
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if (likely(!error))
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seq = blk_flush_cur_seq(rq);
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else
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seq = REQ_FSEQ_DONE;
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switch (seq) {
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case REQ_FSEQ_PREFLUSH:
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case REQ_FSEQ_POSTFLUSH:
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/* queue for flush */
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if (list_empty(pending))
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q->flush_pending_since = jiffies;
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list_move_tail(&rq->flush.list, pending);
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break;
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case REQ_FSEQ_DATA:
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list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
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list_add(&rq->queuelist, &q->queue_head);
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queued = true;
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break;
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case REQ_FSEQ_DONE:
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/*
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* @rq was previously adjusted by blk_flush_issue() for
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* flush sequencing and may already have gone through the
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* flush data request completion path. Restore @rq for
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* normal completion and end it.
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*/
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BUG_ON(!list_empty(&rq->queuelist));
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list_del_init(&rq->flush.list);
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blk_flush_restore_request(rq);
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__blk_end_request_all(rq, error);
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break;
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default:
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BUG();
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}
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return blk_kick_flush(q) | queued;
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}
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static void flush_end_io(struct request *flush_rq, int error)
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{
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struct request_queue *q = flush_rq->q;
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struct list_head *running = &q->flush_queue[q->flush_running_idx];
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bool queued = false;
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struct request *rq, *n;
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BUG_ON(q->flush_pending_idx == q->flush_running_idx);
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/* account completion of the flush request */
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q->flush_running_idx ^= 1;
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elv_completed_request(q, flush_rq);
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/* and push the waiting requests to the next stage */
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list_for_each_entry_safe(rq, n, running, flush.list) {
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unsigned int seq = blk_flush_cur_seq(rq);
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BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
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queued |= blk_flush_complete_seq(rq, seq, error);
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}
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/*
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* Kick the queue to avoid stall for two cases:
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* 1. Moving a request silently to empty queue_head may stall the
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* queue.
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* 2. When flush request is running in non-queueable queue, the
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* queue is hold. Restart the queue after flush request is finished
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* to avoid stall.
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* This function is called from request completion path and calling
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* directly into request_fn may confuse the driver. Always use
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* kblockd.
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*/
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if (queued || q->flush_queue_delayed)
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blk_run_queue_async(q);
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q->flush_queue_delayed = 0;
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}
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/**
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* blk_kick_flush - consider issuing flush request
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* @q: request_queue being kicked
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*
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* Flush related states of @q have changed, consider issuing flush request.
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* Please read the comment at the top of this file for more info.
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*
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* CONTEXT:
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* spin_lock_irq(q->queue_lock)
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*
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* RETURNS:
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* %true if flush was issued, %false otherwise.
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*/
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static bool blk_kick_flush(struct request_queue *q)
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{
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struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
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struct request *first_rq =
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list_first_entry(pending, struct request, flush.list);
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/* C1 described at the top of this file */
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if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
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return false;
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/* C2 and C3 */
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if (!list_empty(&q->flush_data_in_flight) &&
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time_before(jiffies,
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q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
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return false;
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/*
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* Issue flush and toggle pending_idx. This makes pending_idx
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* different from running_idx, which means flush is in flight.
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*/
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blk_rq_init(q, &q->flush_rq);
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q->flush_rq.cmd_type = REQ_TYPE_FS;
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q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
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q->flush_rq.rq_disk = first_rq->rq_disk;
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q->flush_rq.end_io = flush_end_io;
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q->flush_pending_idx ^= 1;
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list_add_tail(&q->flush_rq.queuelist, &q->queue_head);
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return true;
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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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struct request_queue *q = rq->q;
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/*
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* After populating an empty queue, kick it to avoid stall. Read
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* the comment in flush_end_io().
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*/
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if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
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blk_run_queue_async(q);
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}
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/**
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* blk_insert_flush - insert a new FLUSH/FUA request
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* @rq: request to insert
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*
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* To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
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* @rq is being submitted. Analyze what needs to be done and put it on the
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* right queue.
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*
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* CONTEXT:
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* spin_lock_irq(q->queue_lock)
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*/
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void blk_insert_flush(struct request *rq)
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{
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struct request_queue *q = rq->q;
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unsigned int fflags = q->flush_flags; /* may change, cache */
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unsigned int policy = blk_flush_policy(fflags, rq);
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/*
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* @policy now records what operations need to be done. Adjust
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* REQ_FLUSH and FUA for the driver.
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*/
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rq->cmd_flags &= ~REQ_FLUSH;
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if (!(fflags & REQ_FUA))
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rq->cmd_flags &= ~REQ_FUA;
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/*
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* An empty flush handed down from a stacking driver may
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* translate into nothing if the underlying device does not
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* advertise a write-back cache. In this case, simply
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* complete the request.
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*/
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if (!policy) {
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__blk_end_bidi_request(rq, 0, 0, 0);
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return;
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}
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BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
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/*
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* If there's data but flush is not necessary, the request can be
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* processed directly without going through flush machinery. Queue
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* for normal execution.
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*/
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if ((policy & REQ_FSEQ_DATA) &&
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!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
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list_add_tail(&rq->queuelist, &q->queue_head);
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return;
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}
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/*
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* @rq should go through flush machinery. Mark it part of flush
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* sequence and submit for further processing.
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*/
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memset(&rq->flush, 0, sizeof(rq->flush));
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INIT_LIST_HEAD(&rq->flush.list);
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rq->cmd_flags |= REQ_FLUSH_SEQ;
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rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
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rq->end_io = flush_data_end_io;
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blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
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}
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/**
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* blk_abort_flushes - @q is being aborted, abort flush requests
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* @q: request_queue being aborted
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*
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* To be called from elv_abort_queue(). @q is being aborted. Prepare all
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* FLUSH/FUA requests for abortion.
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*
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* CONTEXT:
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* spin_lock_irq(q->queue_lock)
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*/
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void blk_abort_flushes(struct request_queue *q)
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{
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struct request *rq, *n;
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int i;
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/*
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* Requests in flight for data are already owned by the dispatch
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* queue or the device driver. Just restore for normal completion.
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*/
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list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {
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list_del_init(&rq->flush.list);
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blk_flush_restore_request(rq);
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}
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/*
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* We need to give away requests on flush queues. Restore for
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* normal completion and put them on the dispatch queue.
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*/
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for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {
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list_for_each_entry_safe(rq, n, &q->flush_queue[i],
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flush.list) {
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list_del_init(&rq->flush.list);
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blk_flush_restore_request(rq);
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list_add_tail(&rq->queuelist, &q->queue_head);
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}
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}
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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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