| Message ID | 20200406140217.1441858-1-anthony.perard@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,for-5.0] xen-block: Fix double qlist remove and request leak | expand |
> -----Original Message----- > From: Anthony PERARD <anthony.perard@citrix.com> > Sent: 06 April 2020 15:02 > To: qemu-devel@nongnu.org > Cc: qemu-stable@nongnu.org; Anthony PERARD <anthony.perard@citrix.com>; Stefano Stabellini > <sstabellini@kernel.org>; Paul Durrant <paul@xen.org>; Stefan Hajnoczi <stefanha@redhat.com>; Kevin > Wolf <kwolf@redhat.com>; Max Reitz <mreitz@redhat.com>; xen-devel@lists.xenproject.org; qemu- > block@nongnu.org > Subject: [PATCH v2 for-5.0] 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 NIT: I guess you should quote the patch title here as well. > , 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 now the result to the > other end, "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 fix the double QLIST_REMOVE() as we remove the extra s/fix/fixes > call. The second change makes the leak go away because if we want to > call finish_request(), we need to call a function that do all of s/do/does > finish, send response, and release. > > Fixes: bfd0d6366043 ("xen-block: improve response latency") > Signed-off-by: Anthony PERARD <anthony.perard@citrix.com> The code looks ok, so with the cosmetic fixes... Reviewed-by: Paul Durrant <paul@xen.org>
On 06.04.20 16:02, Anthony PERARD wrote: > 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, 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 now the result to the > other end, thus we should call xen_block_send_response() before > releasing a request. > > The first change fix 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 do all of > finish, send response, and release. > > Fixes: bfd0d6366043 ("xen-block: improve response latency") > Signed-off-by: Anthony PERARD <anthony.perard@citrix.com> > --- > hw/block/dataplane/xen-block.c | 48 ++++++++++++---------------------- > 1 file changed, 16 insertions(+), 32 deletions(-) I’m going to send a pull request today anyway, so I hope you won’t mind and let me take this patch to my branch (with Paul’s suggestions incorporated): https://git.xanclic.moe/XanClic/qemu/commits/branch/block Max
diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c index 288a87a814ad..5f8f15778ba5 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 @@ static XenBlockRequest *xen_block_start_request(XenBlockDataPlane *dataplane) return request; } -static void xen_block_finish_request(XenBlockRequest *request) +static void xen_block_complete_request(XenBlockRequest *request) { XenBlockDataPlane *dataplane = request->dataplane; - QLIST_REMOVE(request, list); - dataplane->requests_inflight--; -} + if (xen_block_send_response(request)) { + Error *local_err = NULL; -static void xen_block_release_request(XenBlockRequest *request) -{ - XenBlockDataPlane *dataplane = request->dataplane; + 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--; 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; }
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, 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 now the result to the other end, thus we should call xen_block_send_response() before releasing a request. The first change fix 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 do all of finish, send response, and release. Fixes: bfd0d6366043 ("xen-block: improve response latency") Signed-off-by: Anthony PERARD <anthony.perard@citrix.com> --- hw/block/dataplane/xen-block.c | 48 ++++++++++++---------------------- 1 file changed, 16 insertions(+), 32 deletions(-)