linux-aio: prevent submitting more than MAX_EVENTS
Invoking io_setup(MAX_EVENTS) we ask kernel to create ring buffer for us
with specified number of events. But kernel ring buffer allocation logic
is a bit tricky (ring buffer is page size aligned + some percpu allocation
are required) so eventually more than requested events number is allocated.
From a userspace side we have to follow the convention and should not try
to io_submit() more or logic, which consumes completed events, should be
changed accordingly. The pitfall is in the following sequence:
MAX_EVENTS = 128
io_setup(MAX_EVENTS)
io_submit(MAX_EVENTS)
io_submit(MAX_EVENTS)
/* now 256 events are in-flight */
io_getevents(MAX_EVENTS) = 128
/* we can handle only 128 events at once, to be sure
* that nothing is pended the io_getevents(MAX_EVENTS)
* call must be invoked once more or hang will happen. */
To prevent the hang or reiteration of io_getevents() call this patch
restricts the number of in-flights, which is now limited to MAX_EVENTS.
Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1468415004-31755-1-git-send-email-roman.penyaev@profitbricks.com
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: qemu-devel@nongnu.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/linux-aio.c b/block/linux-aio.c
index 1d702a5..de3548f 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -28,8 +28,6 @@
*/
#define MAX_EVENTS 128
-#define MAX_QUEUED_IO 128
-
struct qemu_laiocb {
BlockAIOCB common;
Coroutine *co;
@@ -44,7 +42,8 @@
typedef struct {
int plugged;
- unsigned int n;
+ unsigned int in_queue;
+ unsigned int in_flight;
bool blocked;
QSIMPLEQ_HEAD(, qemu_laiocb) pending;
} LaioQueue;
@@ -131,6 +130,7 @@
s->event_max = 0;
return; /* no more events */
}
+ s->io_q.in_flight -= s->event_max;
}
/* Reschedule so nested event loops see currently pending completions */
@@ -192,7 +192,8 @@
{
QSIMPLEQ_INIT(&io_q->pending);
io_q->plugged = 0;
- io_q->n = 0;
+ io_q->in_queue = 0;
+ io_q->in_flight = 0;
io_q->blocked = false;
}
@@ -200,14 +201,17 @@
{
int ret, len;
struct qemu_laiocb *aiocb;
- struct iocb *iocbs[MAX_QUEUED_IO];
+ struct iocb *iocbs[MAX_EVENTS];
QSIMPLEQ_HEAD(, qemu_laiocb) completed;
do {
+ if (s->io_q.in_flight >= MAX_EVENTS) {
+ break;
+ }
len = 0;
QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
iocbs[len++] = &aiocb->iocb;
- if (len == MAX_QUEUED_IO) {
+ if (s->io_q.in_flight + len >= MAX_EVENTS) {
break;
}
}
@@ -220,11 +224,12 @@
abort();
}
- s->io_q.n -= ret;
+ s->io_q.in_flight += ret;
+ s->io_q.in_queue -= ret;
aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
} while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
- s->io_q.blocked = (s->io_q.n > 0);
+ s->io_q.blocked = (s->io_q.in_queue > 0);
}
void laio_io_plug(BlockDriverState *bs, LinuxAioState *s)
@@ -264,9 +269,10 @@
io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
- s->io_q.n++;
+ s->io_q.in_queue++;
if (!s->io_q.blocked &&
- (!s->io_q.plugged || s->io_q.n >= MAX_QUEUED_IO)) {
+ (!s->io_q.plugged ||
+ s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
ioq_submit(s);
}
