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Tue, 26 May 2020 11:50:32 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 43A7E4C040; Tue, 26 May 2020 11:50:32 +0000 (GMT) Received: from smtp.tlslab.ibm.com (unknown [9.101.4.1]) by d06av22.portsmouth.uk.ibm.com (Postfix) with SMTP; Tue, 26 May 2020 11:50:32 +0000 (GMT) Received: from bahia.ibmuc.com (sig-9-145-63-64.uk.ibm.com [9.145.63.64]) by smtp.tlslab.ibm.com (Postfix) with ESMTP id 8E0DA22003E; Tue, 26 May 2020 13:50:31 +0200 (CEST) From: Greg Kurz To: qemu-devel@nongnu.org, Peter Maydell Subject: [PULL 4/5] xen/9pfs: yield when there isn't enough room on the ring Date: Tue, 26 May 2020 13:49:31 +0200 Message-Id: <20200526114931.391049-5-groug@kaod.org> X-Mailer: git-send-email 2.21.3 In-Reply-To: <20200526114931.391049-1-groug@kaod.org> References: <20200526114931.391049-1-groug@kaod.org> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-05-26_02:2020-05-26, 2020-05-26 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 adultscore=0 mlxlogscore=999 spamscore=0 clxscore=1034 priorityscore=1501 impostorscore=0 cotscore=-2147483648 mlxscore=0 suspectscore=2 phishscore=0 lowpriorityscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005260087 Received-SPF: softfail client-ip=148.163.156.1; envelope-from=groug@kaod.org; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/26 07:50:51 X-ACL-Warn: Detected OS = Linux 3.x [generic] [fuzzy] X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, KHOP_DYNAMIC=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_SOFTFAIL=0.665, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Christian Schoenebeck , Greg Kurz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Stefano Stabellini Instead of truncating replies, which is problematic, wait until the client reads more data and frees bytes on the reply ring. Do that by calling qemu_coroutine_yield(). The corresponding qemu_coroutine_enter_if_inactive() is called from xen_9pfs_bh upon receiving the next notification from the client. We need to be careful to avoid races in case xen_9pfs_bh and the coroutine are both active at the same time. In xen_9pfs_bh, wait until either the critical section is over (ring->co == NULL) or until the coroutine becomes inactive (qemu_coroutine_yield() was called) before continuing. Then, simply wake up the coroutine if it is inactive. Signed-off-by: Stefano Stabellini Reviewed-by: Christian Schoenebeck Message-Id: <20200521192627.15259-2-sstabellini@kernel.org> Signed-off-by: Greg Kurz --- hw/9pfs/xen-9p-backend.c | 31 +++++++++++++++++++++++++------ 1 file changed, 25 insertions(+), 6 deletions(-) diff --git a/hw/9pfs/xen-9p-backend.c b/hw/9pfs/xen-9p-backend.c index fc197f6c8aaa..3c84c86ab873 100644 --- a/hw/9pfs/xen-9p-backend.c +++ b/hw/9pfs/xen-9p-backend.c @@ -37,6 +37,7 @@ typedef struct Xen9pfsRing { struct iovec *sg; QEMUBH *bh; + Coroutine *co; /* local copies, so that we can read/write PDU data directly from * the ring */ @@ -198,16 +199,20 @@ static void xen_9pfs_init_in_iov_from_pdu(V9fsPDU *pdu, g_free(ring->sg); ring->sg = g_new0(struct iovec, 2); - xen_9pfs_in_sg(ring, ring->sg, &num, pdu->idx, size); + ring->co = qemu_coroutine_self(); + /* make sure other threads see ring->co changes before continuing */ + smp_wmb(); +again: + xen_9pfs_in_sg(ring, ring->sg, &num, pdu->idx, size); buf_size = iov_size(ring->sg, num); if (buf_size < size) { - xen_pv_printf(&xen_9pfs->xendev, 0, "Xen 9pfs request type %d" - "needs %zu bytes, buffer has %zu\n", pdu->id, size, - buf_size); - xen_be_set_state(&xen_9pfs->xendev, XenbusStateClosing); - xen_9pfs_disconnect(&xen_9pfs->xendev); + qemu_coroutine_yield(); + goto again; } + ring->co = NULL; + /* make sure other threads see ring->co changes before continuing */ + smp_wmb(); *piov = ring->sg; *pniov = num; @@ -292,6 +297,20 @@ static int xen_9pfs_receive(Xen9pfsRing *ring) static void xen_9pfs_bh(void *opaque) { Xen9pfsRing *ring = opaque; + bool wait; + +again: + wait = ring->co != NULL && qemu_coroutine_entered(ring->co); + /* paired with the smb_wmb barriers in xen_9pfs_init_in_iov_from_pdu */ + smp_rmb(); + if (wait) { + cpu_relax(); + goto again; + } + + if (ring->co != NULL) { + qemu_coroutine_enter_if_inactive(ring->co); + } xen_9pfs_receive(ring); }