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bh=YkCmyw0pDtYMagunRFX0qUCfWPHTOPKsHXude52+u7Y=; b=h3U5+713w8BcEq+eTawwYCeX3qdqxT5Gg6SROM39ZRO6/Pvwx2xxKbQkWN8y7k8uHMvPT3 QIal2CucwaFmNbVmPna+WMKefA+JgYRYs3LylljrYl62yCeaUgp7lK8QdIZFsNy8VmpG7l jXCTydBLkDiQN/jBzTcZbfq+CPaafkk= X-MC-Unique: OKjnTxW0MASuz0JzWcTuQA-1 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Subject: [PULL 25/29] dma-helpers: prevent dma_blk_cb() vs dma_aio_cancel() race Date: Thu, 23 Feb 2023 19:51:42 +0100 Message-Id: <20230223185146.306454-26-kwolf@redhat.com> In-Reply-To: <20230223185146.306454-1-kwolf@redhat.com> References: <20230223185146.306454-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1677178436818100001 Content-Type: text/plain; charset="utf-8" From: Stefan Hajnoczi dma_blk_cb() only takes the AioContext lock around ->io_func(). That means the rest of dma_blk_cb() is not protected. In particular, the DMAAIOCB field accesses happen outside the lock. There is a race when the main loop thread holds the AioContext lock and invokes scsi_device_purge_requests() -> bdrv_aio_cancel() -> dma_aio_cancel() while an IOThread executes dma_blk_cb(). The dbs->acb field determines how cancellation proceeds. If dma_aio_cancel() sees dbs->acb =3D=3D NULL while dma_blk_cb() is still running, the request can be completed twice (-ECANCELED and the actual return value). The following assertion can occur with virtio-scsi when an IOThread is used: ../hw/scsi/scsi-disk.c:368: scsi_dma_complete: Assertion `r->req.aiocb != =3D NULL' failed. Fix the race by holding the AioContext across dma_blk_cb(). Now dma_aio_cancel() under the AioContext lock will not see inconsistent/intermediate states. Cc: Paolo Bonzini Reviewed-by: Eric Blake Signed-off-by: Stefan Hajnoczi Message-Id: <20230221212218.1378734-3-stefanha@redhat.com> Signed-off-by: Kevin Wolf --- hw/scsi/scsi-disk.c | 4 +--- softmmu/dma-helpers.c | 12 +++++++----- 2 files changed, 8 insertions(+), 8 deletions(-) diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c index 115584f8b9..97c9b1c8cd 100644 --- a/hw/scsi/scsi-disk.c +++ b/hw/scsi/scsi-disk.c @@ -354,13 +354,12 @@ done: scsi_req_unref(&r->req); } =20 +/* Called with AioContext lock held */ static void scsi_dma_complete(void *opaque, int ret) { SCSIDiskReq *r =3D (SCSIDiskReq *)opaque; SCSIDiskState *s =3D DO_UPCAST(SCSIDiskState, qdev, r->req.dev); =20 - aio_context_acquire(blk_get_aio_context(s->qdev.conf.blk)); - assert(r->req.aiocb !=3D NULL); r->req.aiocb =3D NULL; =20 @@ -370,7 +369,6 @@ static void scsi_dma_complete(void *opaque, int ret) block_acct_done(blk_get_stats(s->qdev.conf.blk), &r->acct); } scsi_dma_complete_noio(r, ret); - aio_context_release(blk_get_aio_context(s->qdev.conf.blk)); } =20 static void scsi_read_complete_noio(SCSIDiskReq *r, int ret) diff --git a/softmmu/dma-helpers.c b/softmmu/dma-helpers.c index 7820fec54c..2463964805 100644 --- a/softmmu/dma-helpers.c +++ b/softmmu/dma-helpers.c @@ -113,17 +113,19 @@ static void dma_complete(DMAAIOCB *dbs, int ret) static void dma_blk_cb(void *opaque, int ret) { DMAAIOCB *dbs =3D (DMAAIOCB *)opaque; + AioContext *ctx =3D dbs->ctx; dma_addr_t cur_addr, cur_len; void *mem; =20 trace_dma_blk_cb(dbs, ret); =20 + aio_context_acquire(ctx); dbs->acb =3D NULL; dbs->offset +=3D dbs->iov.size; =20 if (dbs->sg_cur_index =3D=3D dbs->sg->nsg || ret < 0) { dma_complete(dbs, ret); - return; + goto out; } dma_blk_unmap(dbs); =20 @@ -164,9 +166,9 @@ static void dma_blk_cb(void *opaque, int ret) =20 if (dbs->iov.size =3D=3D 0) { trace_dma_map_wait(dbs); - dbs->bh =3D aio_bh_new(dbs->ctx, reschedule_dma, dbs); + dbs->bh =3D aio_bh_new(ctx, reschedule_dma, dbs); cpu_register_map_client(dbs->bh); - return; + goto out; } =20 if (!QEMU_IS_ALIGNED(dbs->iov.size, dbs->align)) { @@ -174,11 +176,11 @@ static void dma_blk_cb(void *opaque, int ret) QEMU_ALIGN_DOWN(dbs->iov.size, dbs->align)= ); } =20 - aio_context_acquire(dbs->ctx); dbs->acb =3D dbs->io_func(dbs->offset, &dbs->iov, dma_blk_cb, dbs, dbs->io_func_opaque); - aio_context_release(dbs->ctx); assert(dbs->acb); +out: + aio_context_release(ctx); } =20 static void dma_aio_cancel(BlockAIOCB *acb) --=20 2.39.2