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xen-block: Fix double qlist remove and request leak 

Commit a31ca6801c ("qemu/queue.h: clear linked list pointers on
remove") revealed that a request was removed twice from a list, once
in xen_block_finish_request() and a second time in
xen_block_release_request() when both function are called from
xen_block_complete_aio(). But also, the `requests_inflight' counter is
decreased twice, and thus became negative.

This is a bug that was introduced in bfd0d63660 ("xen-block: improve
response latency"), where a `finished' list was removed.

That commit also introduced a leak of request in xen_block_do_aio().
That function calls xen_block_finish_request() but the request is
never released after that.

To fix both issue, we do two changes:
- we squash finish_request() and release_request() together as we want
  to remove a request from 'inflight' list to add it to 'freelist'.
- before releasing a request, we need to let the other end know the
  result, thus we should call xen_block_send_response() before
  releasing a request.

The first change fixes the double QLIST_REMOVE() as we remove the extra
call. The second change makes the leak go away because if we want to
call finish_request(), we need to call a function that does all of
finish, send response, and release.

Fixes: bfd0d63660 ("xen-block: improve response latency")
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20200406140217.1441858-1-anthony.perard@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>
[mreitz: Amended commit message as per Paul's suggestions]
Signed-off-by: Max Reitz <mreitz@redhat.com>
stable-5.0
Anthony PERARD 2020-04-06 15:02:17 +01:00 committed by Max Reitz
parent 25fb2e9c39
commit 36d883ba0d
1 changed files with 17 additions and 33 deletions
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50
hw/block/dataplane/xen-block.c
View File

@ -64,6 +64,8 @@ struct XenBlockDataPlane {
AioContext *ctx;
};
static int xen_block_send_response(XenBlockRequest *request);
static void reset_request(XenBlockRequest *request)
{
memset(&request->req, 0, sizeof(request->req));
@ -115,23 +117,26 @@ out:
return request;
}
static void xen_block_finish_request(XenBlockRequest *request)
static void xen_block_complete_request(XenBlockRequest *request)
{
XenBlockDataPlane *dataplane = request->dataplane;
if (xen_block_send_response(request)) {
Error *local_err = NULL;
xen_device_notify_event_channel(dataplane->xendev,
dataplane->event_channel,
&local_err);
if (local_err) {
error_report_err(local_err);
}
}
QLIST_REMOVE(request, list);
dataplane->requests_inflight--;
}
static void xen_block_release_request(XenBlockRequest *request)
{
XenBlockDataPlane *dataplane = request->dataplane;
QLIST_REMOVE(request, list);
reset_request(request);
request->dataplane = dataplane;
QLIST_INSERT_HEAD(&dataplane->freelist, request, list);
dataplane->requests_inflight--;
}
/*
@ -246,7 +251,6 @@ static int xen_block_copy_request(XenBlockRequest *request)
}
static int xen_block_do_aio(XenBlockRequest *request);
static int xen_block_send_response(XenBlockRequest *request);
static void xen_block_complete_aio(void *opaque, int ret)
{
@ -286,7 +290,6 @@ static void xen_block_complete_aio(void *opaque, int ret)
}
request->status = request->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
xen_block_finish_request(request);
switch (request->req.operation) {
case BLKIF_OP_WRITE:
@ -306,17 +309,8 @@ static void xen_block_complete_aio(void *opaque, int ret)
default:
break;
}
if (xen_block_send_response(request)) {
Error *local_err = NULL;
xen_device_notify_event_channel(dataplane->xendev,
dataplane->event_channel,
&local_err);
if (local_err) {
error_report_err(local_err);
}
}
xen_block_release_request(request);
xen_block_complete_request(request);
if (dataplane->more_work) {
qemu_bh_schedule(dataplane->bh);
@ -420,8 +414,8 @@ static int xen_block_do_aio(XenBlockRequest *request)
return 0;
err:
xen_block_finish_request(request);
request->status = BLKIF_RSP_ERROR;
xen_block_complete_request(request);
return -1;
}
@ -575,17 +569,7 @@ static bool xen_block_handle_requests(XenBlockDataPlane *dataplane)
break;
};
if (xen_block_send_response(request)) {
Error *local_err = NULL;
xen_device_notify_event_channel(dataplane->xendev,
dataplane->event_channel,
&local_err);
if (local_err) {
error_report_err(local_err);
}
}
xen_block_release_request(request);
xen_block_complete_request(request);
continue;
}