@@ -198,12 +198,6 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
rq->internal_tag = -1;
rq->start_time_ns = ktime_get_ns();
rq->part = NULL;
- seqcount_init(&rq->gstate_seq);
- u64_stats_init(&rq->aborted_gstate_sync);
- /*
- * See comment of blk_mq_init_request
- */
- WRITE_ONCE(rq->gstate, MQ_RQ_GEN_INC);
}
EXPORT_SYMBOL(blk_rq_init);
@@ -344,7 +344,6 @@ static const char *const rqf_name[] = {
RQF_NAME(STATS),
RQF_NAME(SPECIAL_PAYLOAD),
RQF_NAME(ZONE_WRITE_LOCKED),
- RQF_NAME(MQ_TIMEOUT_EXPIRED),
RQF_NAME(MQ_POLL_SLEPT),
};
#undef RQF_NAME
@@ -332,6 +332,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
#endif
data->ctx->rq_dispatched[op_is_sync(op)]++;
+ refcount_set(&rq->ref, 1);
return rq;
}
@@ -465,13 +466,27 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
}
EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
+static void __blk_mq_free_request(struct request *rq)
+{
+ struct request_queue *q = rq->q;
+ struct blk_mq_ctx *ctx = rq->mq_ctx;
+ struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
+ const int sched_tag = rq->internal_tag;
+
+ if (rq->tag != -1)
+ blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
+ if (sched_tag != -1)
+ blk_mq_put_tag(hctx, hctx->sched_tags, ctx, sched_tag);
+ blk_mq_sched_restart(hctx);
+ blk_queue_exit(q);
+}
+
void blk_mq_free_request(struct request *rq)
{
struct request_queue *q = rq->q;
struct elevator_queue *e = q->elevator;
struct blk_mq_ctx *ctx = rq->mq_ctx;
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
- const int sched_tag = rq->internal_tag;
if (rq->rq_flags & RQF_ELVPRIV) {
if (e && e->type->ops.mq.finish_request)
@@ -494,13 +509,9 @@ void blk_mq_free_request(struct request *rq)
if (blk_rq_rl(rq))
blk_put_rl(blk_rq_rl(rq));
- blk_mq_rq_update_state(rq, MQ_RQ_IDLE);
- if (rq->tag != -1)
- blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
- if (sched_tag != -1)
- blk_mq_put_tag(hctx, hctx->sched_tags, ctx, sched_tag);
- blk_mq_sched_restart(hctx);
- blk_queue_exit(q);
+ WRITE_ONCE(rq->state, MQ_RQ_IDLE);
+ if (refcount_dec_and_test(&rq->ref))
+ __blk_mq_free_request(rq);
}
EXPORT_SYMBOL_GPL(blk_mq_free_request);
@@ -547,8 +558,9 @@ static void __blk_mq_complete_request(struct request *rq)
bool shared = false;
int cpu;
- WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IN_FLIGHT);
- blk_mq_rq_update_state(rq, MQ_RQ_COMPLETE);
+ if (cmpxchg(&rq->state, MQ_RQ_IN_FLIGHT, MQ_RQ_COMPLETE) !=
+ MQ_RQ_IN_FLIGHT)
+ return;
if (rq->internal_tag != -1)
blk_mq_sched_completed_request(rq);
@@ -593,36 +605,6 @@ static void hctx_lock(struct blk_mq_hw_ctx *hctx, int *srcu_idx)
*srcu_idx = srcu_read_lock(hctx->srcu);
}
-static void blk_mq_rq_update_aborted_gstate(struct request *rq, u64 gstate)
-{
- unsigned long flags;
-
- /*
- * blk_mq_rq_aborted_gstate() is used from the completion path and
- * can thus be called from irq context. u64_stats_fetch in the
- * middle of update on the same CPU leads to lockup. Disable irq
- * while updating.
- */
- local_irq_save(flags);
- u64_stats_update_begin(&rq->aborted_gstate_sync);
- rq->aborted_gstate = gstate;
- u64_stats_update_end(&rq->aborted_gstate_sync);
- local_irq_restore(flags);
-}
-
-static u64 blk_mq_rq_aborted_gstate(struct request *rq)
-{
- unsigned int start;
- u64 aborted_gstate;
-
- do {
- start = u64_stats_fetch_begin(&rq->aborted_gstate_sync);
- aborted_gstate = rq->aborted_gstate;
- } while (u64_stats_fetch_retry(&rq->aborted_gstate_sync, start));
-
- return aborted_gstate;
-}
-
/**
* blk_mq_complete_request - end I/O on a request
* @rq: the request being processed
@@ -633,28 +615,9 @@ static u64 blk_mq_rq_aborted_gstate(struct request *rq)
**/
void blk_mq_complete_request(struct request *rq)
{
- struct request_queue *q = rq->q;
- struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, rq->mq_ctx->cpu);
- int srcu_idx;
-
- if (unlikely(blk_should_fake_timeout(q)))
+ if (unlikely(blk_should_fake_timeout(rq->q)))
return;
-
- /*
- * If @rq->aborted_gstate equals the current instance, timeout is
- * claiming @rq and we lost. This is synchronized through
- * hctx_lock(). See blk_mq_timeout_work() for details.
- *
- * Completion path never blocks and we can directly use RCU here
- * instead of hctx_lock() which can be either RCU or SRCU.
- * However, that would complicate paths which want to synchronize
- * against us. Let stay in sync with the issue path so that
- * hctx_lock() covers both issue and completion paths.
- */
- hctx_lock(hctx, &srcu_idx);
- if (blk_mq_rq_aborted_gstate(rq) != rq->gstate)
- __blk_mq_complete_request(rq);
- hctx_unlock(hctx, srcu_idx);
+ __blk_mq_complete_request(rq);
}
EXPORT_SYMBOL(blk_mq_complete_request);
@@ -683,25 +646,8 @@ void blk_mq_start_request(struct request *rq)
WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE);
- /*
- * Mark @rq in-flight which also advances the generation number,
- * and register for timeout. Protect with a seqcount to allow the
- * timeout path to read both @rq->gstate and @rq->deadline
- * coherently.
- *
- * This is the only place where a request is marked in-flight. If
- * the timeout path reads an in-flight @rq->gstate, the
- * @rq->deadline it reads together under @rq->gstate_seq is
- * guaranteed to be the matching one.
- */
- preempt_disable();
- write_seqcount_begin(&rq->gstate_seq);
-
blk_add_timer(rq);
- blk_mq_rq_update_state(rq, MQ_RQ_IN_FLIGHT);
-
- write_seqcount_end(&rq->gstate_seq);
- preempt_enable();
+ WRITE_ONCE(rq->state, MQ_RQ_IN_FLIGHT);
if (q->dma_drain_size && blk_rq_bytes(rq)) {
/*
@@ -714,11 +660,6 @@ void blk_mq_start_request(struct request *rq)
}
EXPORT_SYMBOL(blk_mq_start_request);
-/*
- * When we reach here because queue is busy, it's safe to change the state
- * to IDLE without checking @rq->aborted_gstate because we should still be
- * holding the RCU read lock and thus protected against timeout.
- */
static void __blk_mq_requeue_request(struct request *rq)
{
struct request_queue *q = rq->q;
@@ -728,8 +669,8 @@ static void __blk_mq_requeue_request(struct request *rq)
trace_block_rq_requeue(q, rq);
wbt_requeue(q->rq_wb, rq);
- if (blk_mq_rq_state(rq) != MQ_RQ_IDLE) {
- blk_mq_rq_update_state(rq, MQ_RQ_IDLE);
+ if (blk_mq_request_started(rq)) {
+ WRITE_ONCE(rq->state, MQ_RQ_IDLE);
if (q->dma_drain_size && blk_rq_bytes(rq))
rq->nr_phys_segments--;
}
@@ -827,33 +768,20 @@ struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
}
EXPORT_SYMBOL(blk_mq_tag_to_rq);
-struct blk_mq_timeout_data {
- unsigned long next;
- unsigned int next_set;
- unsigned int nr_expired;
-};
-
static void blk_mq_rq_timed_out(struct request *req, bool reserved)
{
const struct blk_mq_ops *ops = req->q->mq_ops;
enum blk_eh_timer_return ret = BLK_EH_RESET_TIMER;
- req->rq_flags |= RQF_MQ_TIMEOUT_EXPIRED;
-
if (ops->timeout)
ret = ops->timeout(req, reserved);
switch (ret) {
case BLK_EH_HANDLED:
- __blk_mq_complete_request(req);
+ if (blk_mq_rq_state(req) == MQ_RQ_IN_FLIGHT)
+ __blk_mq_complete_request(req);
break;
case BLK_EH_RESET_TIMER:
- /*
- * As nothing prevents from completion happening while
- * ->aborted_gstate is set, this may lead to ignored
- * completions and further spurious timeouts.
- */
- blk_mq_rq_update_aborted_gstate(req, 0);
blk_add_timer(req);
break;
case BLK_EH_NOT_HANDLED:
@@ -864,64 +792,65 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
}
}
-static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
- struct request *rq, void *priv, bool reserved)
+static bool blk_mq_req_expired(struct request *rq, unsigned long *next)
{
- struct blk_mq_timeout_data *data = priv;
- unsigned long gstate, deadline;
- int start;
+ unsigned long deadline;
- might_sleep();
-
- if (rq->rq_flags & RQF_MQ_TIMEOUT_EXPIRED)
- return;
+ if (blk_mq_rq_state(rq) != MQ_RQ_IN_FLIGHT)
+ return false;
- /* read coherent snapshots of @rq->state_gen and @rq->deadline */
- while (true) {
- start = read_seqcount_begin(&rq->gstate_seq);
- gstate = READ_ONCE(rq->gstate);
- deadline = blk_rq_deadline(rq);
- if (!read_seqcount_retry(&rq->gstate_seq, start))
- break;
- cond_resched();
- }
+ deadline = blk_rq_deadline(rq);
+ if (time_after_eq(jiffies, deadline))
+ return true;
- /* if in-flight && overdue, mark for abortion */
- if ((gstate & MQ_RQ_STATE_MASK) == MQ_RQ_IN_FLIGHT &&
- time_after_eq(jiffies, deadline)) {
- blk_mq_rq_update_aborted_gstate(rq, gstate);
- data->nr_expired++;
- hctx->nr_expired++;
- } else if (!data->next_set || time_after(data->next, deadline)) {
- data->next = deadline;
- data->next_set = 1;
- }
+ if (*next == 0)
+ *next = deadline;
+ else if (time_after(*next, deadline))
+ *next = deadline;
+ return false;
}
-static void blk_mq_terminate_expired(struct blk_mq_hw_ctx *hctx,
+static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
struct request *rq, void *priv, bool reserved)
{
+ unsigned long *next = priv;
+
/*
- * We marked @rq->aborted_gstate and waited for RCU. If there were
- * completions that we lost to, they would have finished and
- * updated @rq->gstate by now; otherwise, the completion path is
- * now guaranteed to see @rq->aborted_gstate and yield. If
- * @rq->aborted_gstate still matches @rq->gstate, @rq is ours.
+ * Just do a quick check if it is expired before locking the request in
+ * so we're not unnecessarilly synchronizing across CPUs.
*/
- if (!(rq->rq_flags & RQF_MQ_TIMEOUT_EXPIRED) &&
- READ_ONCE(rq->gstate) == rq->aborted_gstate)
+ if (!blk_mq_req_expired(rq, next))
+ return;
+
+ /*
+ * We have reason to believe the request may be expired. Take a
+ * reference on the request to lock this request lifetime into its
+ * currently allocated context to prevent it from being reallocated in
+ * the event the completion by-passes this timeout handler.
+ *
+ * If the reference was already released, then the driver beat the
+ * timeout handler to posting a natural completion.
+ */
+ if (!refcount_inc_not_zero(&rq->ref))
+ return;
+
+ /*
+ * The request is now locked and cannot be reallocated underneath the
+ * timeout handler's processing. Re-verify this exact request is truly
+ * expired; if it is not expired, then the request was completed and
+ * reallocated as a new request.
+ */
+ if (blk_mq_req_expired(rq, next))
blk_mq_rq_timed_out(rq, reserved);
+ if (refcount_dec_and_test(&rq->ref))
+ __blk_mq_free_request(rq);
}
static void blk_mq_timeout_work(struct work_struct *work)
{
struct request_queue *q =
container_of(work, struct request_queue, timeout_work);
- struct blk_mq_timeout_data data = {
- .next = 0,
- .next_set = 0,
- .nr_expired = 0,
- };
+ unsigned long next = 0;
struct blk_mq_hw_ctx *hctx;
int i;
@@ -941,39 +870,10 @@ static void blk_mq_timeout_work(struct work_struct *work)
if (!percpu_ref_tryget(&q->q_usage_counter))
return;
- /* scan for the expired ones and set their ->aborted_gstate */
- blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &data);
-
- if (data.nr_expired) {
- bool has_rcu = false;
-
- /*
- * Wait till everyone sees ->aborted_gstate. The
- * sequential waits for SRCUs aren't ideal. If this ever
- * becomes a problem, we can add per-hw_ctx rcu_head and
- * wait in parallel.
- */
- queue_for_each_hw_ctx(q, hctx, i) {
- if (!hctx->nr_expired)
- continue;
-
- if (!(hctx->flags & BLK_MQ_F_BLOCKING))
- has_rcu = true;
- else
- synchronize_srcu(hctx->srcu);
-
- hctx->nr_expired = 0;
- }
- if (has_rcu)
- synchronize_rcu();
+ blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next);
- /* terminate the ones we won */
- blk_mq_queue_tag_busy_iter(q, blk_mq_terminate_expired, NULL);
- }
-
- if (data.next_set) {
- data.next = blk_rq_timeout(round_jiffies_up(data.next));
- mod_timer(&q->timeout, data.next);
+ if (next != 0) {
+ mod_timer(&q->timeout, next);
} else {
/*
* Request timeouts are handled as a forward rolling timer. If
@@ -2049,15 +1949,7 @@ static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
return ret;
}
- seqcount_init(&rq->gstate_seq);
- u64_stats_init(&rq->aborted_gstate_sync);
- /*
- * start gstate with gen 1 instead of 0, otherwise it will be equal
- * to aborted_gstate, and be identified timed out by
- * blk_mq_terminate_expired.
- */
- WRITE_ONCE(rq->gstate, MQ_RQ_GEN_INC);
-
+ WRITE_ONCE(rq->state, MQ_RQ_IDLE);
return 0;
}
@@ -30,20 +30,6 @@ struct blk_mq_ctx {
struct kobject kobj;
} ____cacheline_aligned_in_smp;
-/*
- * Bits for request->gstate. The lower two bits carry MQ_RQ_* state value
- * and the upper bits the generation number.
- */
-enum mq_rq_state {
- MQ_RQ_IDLE = 0,
- MQ_RQ_IN_FLIGHT = 1,
- MQ_RQ_COMPLETE = 2,
-
- MQ_RQ_STATE_BITS = 2,
- MQ_RQ_STATE_MASK = (1 << MQ_RQ_STATE_BITS) - 1,
- MQ_RQ_GEN_INC = 1 << MQ_RQ_STATE_BITS,
-};
-
void blk_mq_freeze_queue(struct request_queue *q);
void blk_mq_free_queue(struct request_queue *q);
int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
@@ -107,33 +93,9 @@ void blk_mq_release(struct request_queue *q);
* blk_mq_rq_state() - read the current MQ_RQ_* state of a request
* @rq: target request.
*/
-static inline int blk_mq_rq_state(struct request *rq)
+static inline enum mq_rq_state blk_mq_rq_state(struct request *rq)
{
- return READ_ONCE(rq->gstate) & MQ_RQ_STATE_MASK;
-}
-
-/**
- * blk_mq_rq_update_state() - set the current MQ_RQ_* state of a request
- * @rq: target request.
- * @state: new state to set.
- *
- * Set @rq's state to @state. The caller is responsible for ensuring that
- * there are no other updaters. A request can transition into IN_FLIGHT
- * only from IDLE and doing so increments the generation number.
- */
-static inline void blk_mq_rq_update_state(struct request *rq,
- enum mq_rq_state state)
-{
- u64 old_val = READ_ONCE(rq->gstate);
- u64 new_val = (old_val & ~MQ_RQ_STATE_MASK) | state;
-
- if (state == MQ_RQ_IN_FLIGHT) {
- WARN_ON_ONCE((old_val & MQ_RQ_STATE_MASK) != MQ_RQ_IDLE);
- new_val += MQ_RQ_GEN_INC;
- }
-
- /* avoid exposing interim values */
- WRITE_ONCE(rq->gstate, new_val);
+ return READ_ONCE(rq->state);
}
static inline struct blk_mq_ctx *__blk_mq_get_ctx(struct request_queue *q,
@@ -214,7 +214,6 @@ void blk_add_timer(struct request *req)
req->timeout = q->rq_timeout;
blk_rq_set_deadline(req, jiffies + req->timeout);
- req->rq_flags &= ~RQF_MQ_TIMEOUT_EXPIRED;
/*
* Only the non-mq case needs to add the request to a protected list.
@@ -125,15 +125,22 @@ typedef __u32 __bitwise req_flags_t;
#define RQF_SPECIAL_PAYLOAD ((__force req_flags_t)(1 << 18))
/* The per-zone write lock is held for this request */
#define RQF_ZONE_WRITE_LOCKED ((__force req_flags_t)(1 << 19))
-/* timeout is expired */
-#define RQF_MQ_TIMEOUT_EXPIRED ((__force req_flags_t)(1 << 20))
/* already slept for hybrid poll */
-#define RQF_MQ_POLL_SLEPT ((__force req_flags_t)(1 << 21))
+#define RQF_MQ_POLL_SLEPT ((__force req_flags_t)(1 << 20))
/* flags that prevent us from merging requests: */
#define RQF_NOMERGE_FLAGS \
(RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ | RQF_SPECIAL_PAYLOAD)
+/*
+ * Request state for blk-mq.
+ */
+enum mq_rq_state {
+ MQ_RQ_IDLE = 0,
+ MQ_RQ_IN_FLIGHT = 1,
+ MQ_RQ_COMPLETE = 2,
+};
+
/*
* Try to put the fields that are referenced together in the same cacheline.
*
@@ -236,26 +243,8 @@ struct request {
unsigned int extra_len; /* length of alignment and padding */
- /*
- * On blk-mq, the lower bits of ->gstate (generation number and
- * state) carry the MQ_RQ_* state value and the upper bits the
- * generation number which is monotonically incremented and used to
- * distinguish the reuse instances.
- *
- * ->gstate_seq allows updates to ->gstate and other fields
- * (currently ->deadline) during request start to be read
- * atomically from the timeout path, so that it can operate on a
- * coherent set of information.
- */
- seqcount_t gstate_seq;
- u64 gstate;
-
- /*
- * ->aborted_gstate is used by the timeout to claim a specific
- * recycle instance of this request. See blk_mq_timeout_work().
- */
- struct u64_stats_sync aborted_gstate_sync;
- u64 aborted_gstate;
+ enum mq_rq_state state;
+ refcount_t ref;
/* access through blk_rq_set_deadline, blk_rq_deadline */
unsigned long __deadline;