nbd: handle unexpected replies better

If the server or network is misbehaving and we get an unexpected reply
we can sometimes miss the request not being started and wait on a
request and never get a response, or even double complete the same
request.  Fix this by replacing the send_complete completion with just a
per command lock.  Add a per command cookie as well so that we can know
if we're getting a double completion for a previous event.  Also check
to make sure we dont have REQUEUED set as that means we raced with the
timeout handler and need to just let the retry occur.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index f8cf7d4..3fb95c8 100644 (file)
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -116,11 +116,12 @@ struct nbd_device {
 
 struct nbd_cmd {
        struct nbd_device *nbd;
+       struct mutex lock;
        int index;
        int cookie;
-       struct completion send_complete;
        blk_status_t status;
        unsigned long flags;
+       u32 cmd_cookie;
 };
 
 #if IS_ENABLED(CONFIG_DEBUG_FS)
@@ -157,6 +158,27 @@ static void nbd_requeue_cmd(struct nbd_cmd *cmd)
                blk_mq_requeue_request(req, true);
 }
 
+#define NBD_COOKIE_BITS 32
+
+static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
+{
+       struct request *req = blk_mq_rq_from_pdu(cmd);
+       u32 tag = blk_mq_unique_tag(req);
+       u64 cookie = cmd->cmd_cookie;
+
+       return (cookie << NBD_COOKIE_BITS) | tag;
+}
+
+static u32 nbd_handle_to_tag(u64 handle)
+{
+       return (u32)handle;
+}
+
+static u32 nbd_handle_to_cookie(u64 handle)
+{
+       return (u32)(handle >> NBD_COOKIE_BITS);
+}
+
 static const char *nbdcmd_to_ascii(int cmd)
 {
        switch (cmd) {
@@ -330,6 +352,9 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
        }
        config = nbd->config;
 
+       if (!mutex_trylock(&cmd->lock))
+               return BLK_EH_RESET_TIMER;
+
        if (config->num_connections > 1) {
                dev_err_ratelimited(nbd_to_dev(nbd),
                                    "Connection timed out, retrying (%d/%d alive)\n",
@@ -354,6 +379,7 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
                                        nbd_mark_nsock_dead(nbd, nsock, 1);
                                mutex_unlock(&nsock->tx_lock);
                        }
+                       mutex_unlock(&cmd->lock);
                        nbd_requeue_cmd(cmd);
                        nbd_config_put(nbd);
                        return BLK_EH_DONE;
@@ -364,6 +390,7 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
        }
        set_bit(NBD_TIMEDOUT, &config->runtime_flags);
        cmd->status = BLK_STS_IOERR;
+       mutex_unlock(&cmd->lock);
        sock_shutdown(nbd);
        nbd_config_put(nbd);
 done:
@@ -441,9 +468,9 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
        struct iov_iter from;
        unsigned long size = blk_rq_bytes(req);
        struct bio *bio;
+       u64 handle;
        u32 type;
        u32 nbd_cmd_flags = 0;
-       u32 tag = blk_mq_unique_tag(req);
        int sent = nsock->sent, skip = 0;
 
        iov_iter_kvec(&from, WRITE | ITER_KVEC, &iov, 1, sizeof(request));
@@ -485,6 +512,8 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
                        goto send_pages;
                }
                iov_iter_advance(&from, sent);
+       } else {
+               cmd->cmd_cookie++;
        }
        cmd->index = index;
        cmd->cookie = nsock->cookie;
@@ -493,7 +522,8 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
                request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
                request.len = htonl(size);
        }
-       memcpy(request.handle, &tag, sizeof(tag));
+       handle = nbd_cmd_handle(cmd);
+       memcpy(request.handle, &handle, sizeof(handle));
 
        dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
                req, nbdcmd_to_ascii(type),
@@ -586,10 +616,12 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
        struct nbd_reply reply;
        struct nbd_cmd *cmd;
        struct request *req = NULL;
+       u64 handle;
        u16 hwq;
        u32 tag;
        struct kvec iov = {.iov_base = &reply, .iov_len = sizeof(reply)};
        struct iov_iter to;
+       int ret = 0;
 
        reply.magic = 0;
        iov_iter_kvec(&to, READ | ITER_KVEC, &iov, 1, sizeof(reply));
@@ -607,8 +639,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
                return ERR_PTR(-EPROTO);
        }
 
-       memcpy(&tag, reply.handle, sizeof(u32));
-
+       memcpy(&handle, reply.handle, sizeof(handle));
+       tag = nbd_handle_to_tag(handle);
        hwq = blk_mq_unique_tag_to_hwq(tag);
        if (hwq < nbd->tag_set.nr_hw_queues)
                req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
@@ -619,11 +651,25 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
                return ERR_PTR(-ENOENT);
        }
        cmd = blk_mq_rq_to_pdu(req);
+
+       mutex_lock(&cmd->lock);
+       if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
+               dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
+                       req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
+               ret = -ENOENT;
+               goto out;
+       }
+       if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
+               dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
+                       req);
+               ret = -ENOENT;
+               goto out;
+       }
        if (ntohl(reply.error)) {
                dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
                        ntohl(reply.error));
                cmd->status = BLK_STS_IOERR;
-               return cmd;
+               goto out;
        }
 
        dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
@@ -648,18 +694,18 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
                                if (nbd_disconnected(config) ||
                                    config->num_connections <= 1) {
                                        cmd->status = BLK_STS_IOERR;
-                                       return cmd;
+                                       goto out;
                                }
-                               return ERR_PTR(-EIO);
+                               ret = -EIO;
+                               goto out;
                        }
                        dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
                                req, bvec.bv_len);
                }
-       } else {
-               /* See the comment in nbd_queue_rq. */
-               wait_for_completion(&cmd->send_complete);
        }
-       return cmd;
+out:
+       mutex_unlock(&cmd->lock);
+       return ret ? ERR_PTR(ret) : cmd;
 }
 
 static void recv_work(struct work_struct *work)
@@ -855,7 +901,7 @@ static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
         * that the server is misbehaving (or there was an error) before we're
         * done sending everything over the wire.
         */
-       init_completion(&cmd->send_complete);
+       mutex_lock(&cmd->lock);
        clear_bit(NBD_CMD_REQUEUED, &cmd->flags);
 
        /* We can be called directly from the user space process, which means we
@@ -868,7 +914,7 @@ static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
                ret = BLK_STS_IOERR;
        else if (!ret)
                ret = BLK_STS_OK;
-       complete(&cmd->send_complete);
+       mutex_unlock(&cmd->lock);
 
        return ret;
 }
@@ -1475,6 +1521,7 @@ static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
        struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
        cmd->nbd = set->driver_data;
        cmd->flags = 0;
+       mutex_init(&cmd->lock);
        return 0;
 }