* [PATCH 1/2] Revert "mirror: Don't let an operation wait for itself"
2020-03-25 17:23 [PATCH 0/2] mirror: Fix hang (operation waiting for itself/circular dependency) Kevin Wolf
@ 2020-03-25 17:23 ` Kevin Wolf
2020-03-25 17:36 ` Eric Blake
2020-03-25 17:23 ` [PATCH 2/2] mirror: Wait only for in-flight operations Kevin Wolf
2020-03-25 17:49 ` [PATCH 0/2] mirror: Fix hang (operation waiting for itself/circular dependency) Kevin Wolf
2 siblings, 1 reply; 6+ messages in thread
From: Kevin Wolf @ 2020-03-25 17:23 UTC (permalink / raw)
To: qemu-block; +Cc: kwolf, jsnow, qemu-devel, mreitz
This reverts commit 7e6c4ff792734e196c8ca82564c56b5e7c6288ca.
The fix was incomplete as it only protected against requests waiting for
themselves, but not against requests waiting for each other. We need a
different solution.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/mirror.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)
diff --git a/block/mirror.c b/block/mirror.c
index 447051dbc6..393131b135 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -283,14 +283,11 @@ static int mirror_cow_align(MirrorBlockJob *s, int64_t *offset,
}
static inline void coroutine_fn
-mirror_wait_for_any_operation(MirrorBlockJob *s, MirrorOp *self, bool active)
+mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
{
MirrorOp *op;
QTAILQ_FOREACH(op, &s->ops_in_flight, next) {
- if (self == op) {
- continue;
- }
/* Do not wait on pseudo ops, because it may in turn wait on
* some other operation to start, which may in fact be the
* caller of this function. Since there is only one pseudo op
@@ -305,10 +302,10 @@ mirror_wait_for_any_operation(MirrorBlockJob *s, MirrorOp *self, bool active)
}
static inline void coroutine_fn
-mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s, MirrorOp *self)
+mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s)
{
/* Only non-active operations use up in-flight slots */
- mirror_wait_for_any_operation(s, self, false);
+ mirror_wait_for_any_operation(s, false);
}
/* Perform a mirror copy operation.
@@ -351,7 +348,7 @@ static void coroutine_fn mirror_co_read(void *opaque)
while (s->buf_free_count < nb_chunks) {
trace_mirror_yield_in_flight(s, op->offset, s->in_flight);
- mirror_wait_for_free_in_flight_slot(s, op);
+ mirror_wait_for_free_in_flight_slot(s);
}
/* Now make a QEMUIOVector taking enough granularity-sized chunks
@@ -558,7 +555,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
while (s->in_flight >= MAX_IN_FLIGHT) {
trace_mirror_yield_in_flight(s, offset, s->in_flight);
- mirror_wait_for_free_in_flight_slot(s, pseudo_op);
+ mirror_wait_for_free_in_flight_slot(s);
}
if (s->ret < 0) {
@@ -612,7 +609,7 @@ static void mirror_free_init(MirrorBlockJob *s)
static void coroutine_fn mirror_wait_for_all_io(MirrorBlockJob *s)
{
while (s->in_flight > 0) {
- mirror_wait_for_free_in_flight_slot(s, NULL);
+ mirror_wait_for_free_in_flight_slot(s);
}
}
@@ -809,7 +806,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
if (s->in_flight >= MAX_IN_FLIGHT) {
trace_mirror_yield(s, UINT64_MAX, s->buf_free_count,
s->in_flight);
- mirror_wait_for_free_in_flight_slot(s, NULL);
+ mirror_wait_for_free_in_flight_slot(s);
continue;
}
@@ -962,7 +959,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
/* Do not start passive operations while there are active
* writes in progress */
while (s->in_active_write_counter) {
- mirror_wait_for_any_operation(s, NULL, true);
+ mirror_wait_for_any_operation(s, true);
}
if (s->ret < 0) {
@@ -988,7 +985,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
if (s->in_flight >= MAX_IN_FLIGHT || s->buf_free_count == 0 ||
(cnt == 0 && s->in_flight > 0)) {
trace_mirror_yield(s, cnt, s->buf_free_count, s->in_flight);
- mirror_wait_for_free_in_flight_slot(s, NULL);
+ mirror_wait_for_free_in_flight_slot(s);
continue;
} else if (cnt != 0) {
delay_ns = mirror_iteration(s);
--
2.20.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH 2/2] mirror: Wait only for in-flight operations
2020-03-25 17:23 [PATCH 0/2] mirror: Fix hang (operation waiting for itself/circular dependency) Kevin Wolf
2020-03-25 17:23 ` [PATCH 1/2] Revert "mirror: Don't let an operation wait for itself" Kevin Wolf
@ 2020-03-25 17:23 ` Kevin Wolf
2020-03-25 17:39 ` Eric Blake
2020-03-25 17:49 ` [PATCH 0/2] mirror: Fix hang (operation waiting for itself/circular dependency) Kevin Wolf
2 siblings, 1 reply; 6+ messages in thread
From: Kevin Wolf @ 2020-03-25 17:23 UTC (permalink / raw)
To: qemu-block; +Cc: kwolf, jsnow, qemu-devel, mreitz
mirror_wait_for_free_in_flight_slot() just picks a random operation to
wait for. However, a MirrorOp is already in s->ops_in_flight when
mirror_co_read() waits for free slots, so if not enough slots are
immediately available, an operation can end up waiting for itself, or
two or more operations can wait for each other to complete, which
results in a hang.
Fix this by adding a flag to MirrorOp that tells us if the request is
already in flight (and therefore occupies slots that it will later
free), and picking only such operations for waiting.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1794692
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/mirror.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/block/mirror.c b/block/mirror.c
index 393131b135..7fef52ded2 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -102,6 +102,7 @@ struct MirrorOp {
bool is_pseudo_op;
bool is_active_write;
+ bool is_in_flight;
CoQueue waiting_requests;
Coroutine *co;
@@ -293,7 +294,9 @@ mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
* caller of this function. Since there is only one pseudo op
* at any given time, we will always find some real operation
* to wait on. */
- if (!op->is_pseudo_op && op->is_active_write == active) {
+ if (!op->is_pseudo_op && op->is_in_flight &&
+ op->is_active_write == active)
+ {
qemu_co_queue_wait(&op->waiting_requests, NULL);
return;
}
@@ -367,6 +370,7 @@ static void coroutine_fn mirror_co_read(void *opaque)
/* Copy the dirty cluster. */
s->in_flight++;
s->bytes_in_flight += op->bytes;
+ op->is_in_flight = true;
trace_mirror_one_iteration(s, op->offset, op->bytes);
ret = bdrv_co_preadv(s->mirror_top_bs->backing, op->offset, op->bytes,
@@ -382,6 +386,7 @@ static void coroutine_fn mirror_co_zero(void *opaque)
op->s->in_flight++;
op->s->bytes_in_flight += op->bytes;
*op->bytes_handled = op->bytes;
+ op->is_in_flight = true;
ret = blk_co_pwrite_zeroes(op->s->target, op->offset, op->bytes,
op->s->unmap ? BDRV_REQ_MAY_UNMAP : 0);
@@ -396,6 +401,7 @@ static void coroutine_fn mirror_co_discard(void *opaque)
op->s->in_flight++;
op->s->bytes_in_flight += op->bytes;
*op->bytes_handled = op->bytes;
+ op->is_in_flight = true;
ret = blk_co_pdiscard(op->s->target, op->offset, op->bytes);
mirror_write_complete(op, ret);
--
2.20.1
^ permalink raw reply related [flat|nested] 6+ messages in thread