* [PATCH 1/2] mirror: Store MirrorOp.co for debuggability
2020-01-28 15:17 [PATCH 0/2] mirror: Fix hang (operation waiting for itself) Kevin Wolf
@ 2020-01-28 15:17 ` Kevin Wolf
2020-01-28 16:26 ` Eric Blake
2020-01-28 15:17 ` [PATCH 2/2] mirror: Don't let an operation wait for itself Kevin Wolf
1 sibling, 1 reply; 5+ messages in thread
From: Kevin Wolf @ 2020-01-28 15:17 UTC (permalink / raw)
To: qemu-block; +Cc: kwolf, jsnow, qemu-devel, mreitz
If a coroutine is launched, but the coroutine pointer isn't stored
anywhere, debugging any problems inside the coroutine is quite hard.
Let's store the coroutine pointer of a mirror operation in MirrorOp to
have it available in the debugger.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/mirror.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/block/mirror.c b/block/mirror.c
index f0f2d9dff1..8959e4255f 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -103,6 +103,7 @@ struct MirrorOp {
bool is_pseudo_op;
bool is_active_write;
CoQueue waiting_requests;
+ Coroutine *co;
QTAILQ_ENTRY(MirrorOp) next;
};
@@ -429,6 +430,7 @@ static unsigned mirror_perform(MirrorBlockJob *s, int64_t offset,
default:
abort();
}
+ op->co = co;
QTAILQ_INSERT_TAIL(&s->ops_in_flight, op, next);
qemu_coroutine_enter(co);
--
2.20.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH 2/2] mirror: Don't let an operation wait for itself
2020-01-28 15:17 [PATCH 0/2] mirror: Fix hang (operation waiting for itself) Kevin Wolf
2020-01-28 15:17 ` [PATCH 1/2] mirror: Store MirrorOp.co for debuggability Kevin Wolf
@ 2020-01-28 15:17 ` Kevin Wolf
2020-01-28 16:27 ` Eric Blake
1 sibling, 1 reply; 5+ messages in thread
From: Kevin Wolf @ 2020-01-28 15:17 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, when mirror_co_read() waits for free slots, its
MirrorOp is already in s->ops_in_flight, so if not enough slots are
immediately available, an operation can end up waiting for itself to
complete, which results in a hang.
Fix this by passing the current MirrorOp and skipping this operation
when picking an operation to wait for.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1794692
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/mirror.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/block/mirror.c b/block/mirror.c
index 8959e4255f..cacbc70014 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -283,11 +283,14 @@ static int mirror_cow_align(MirrorBlockJob *s, int64_t *offset,
}
static inline void coroutine_fn
-mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
+mirror_wait_for_any_operation(MirrorBlockJob *s, MirrorOp *self, 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
@@ -302,10 +305,10 @@ mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
}
static inline void coroutine_fn
-mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s)
+mirror_wait_for_free_in_flight_slot(MirrorBlockJob *s, MirrorOp *self)
{
/* Only non-active operations use up in-flight slots */
- mirror_wait_for_any_operation(s, false);
+ mirror_wait_for_any_operation(s, self, false);
}
/* Perform a mirror copy operation.
@@ -348,7 +351,7 @@ 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);
+ mirror_wait_for_free_in_flight_slot(s, op);
}
/* Now make a QEMUIOVector taking enough granularity-sized chunks
@@ -555,7 +558,7 @@ 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);
+ mirror_wait_for_free_in_flight_slot(s, pseudo_op);
}
if (s->ret < 0) {
@@ -609,7 +612,7 @@ 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);
+ mirror_wait_for_free_in_flight_slot(s, NULL);
}
}
@@ -794,7 +797,7 @@ 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);
+ mirror_wait_for_free_in_flight_slot(s, NULL);
continue;
}
@@ -947,7 +950,7 @@ 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, true);
+ mirror_wait_for_any_operation(s, NULL, true);
}
if (s->ret < 0) {
@@ -973,7 +976,7 @@ 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);
+ mirror_wait_for_free_in_flight_slot(s, NULL);
continue;
} else if (cnt != 0) {
delay_ns = mirror_iteration(s);
--
2.20.1
^ permalink raw reply related [flat|nested] 5+ messages in thread