From 36d883ba0de8a281072ded2b51e0a711fd002139 Mon Sep 17 00:00:00 2001 From: Anthony PERARD Date: Mon, 6 Apr 2020 15:02:17 +0100 Subject: [PATCH] xen-block: Fix double qlist remove and request leak Commit a31ca6801c02 ("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 bfd0d6366043 ("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: bfd0d6366043 ("xen-block: improve response latency") Signed-off-by: Anthony PERARD Message-Id: <20200406140217.1441858-1-anthony.perard@citrix.com> Reviewed-by: Paul Durrant [mreitz: Amended commit message as per Paul's suggestions] Signed-off-by: Max Reitz --- hw/block/dataplane/xen-block.c | 50 ++++++++++++---------------------- 1 file changed, 17 insertions(+), 33 deletions(-) diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c index 288a87a814..5f8f15778b 100644 --- a/hw/block/dataplane/xen-block.c +++ b/hw/block/dataplane/xen-block.c @@ -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; }