On Thu, Oct 17, 2024 at 05:47:53PM +0200, Kevin Wolf wrote: > Am 17.10.2024 um 13:36 hat Ming Lei geschrieben: > > nbd driver sends request header and payload with multiple call of > > sock_sendmsg, and partial sending can't be avoided. However, nbd driver > > returns BLK_STS_RESOURCE to block core in this situation. This way causes > > one issue: request->tag may change in the next run of nbd_queue_rq(), but > > the original old tag has been sent as part of header cookie, this way > > confuses nbd driver reply handling, since the real request can't be > > retrieved any more with the obsolete old tag. > > > > Fix it by retrying sending directly, this way is reasonable & safe since > > nothing can move on if the current hw queue(socket) has pending request, > > and unnecessary requeue can be avoided in this way. > > > > Cc: vincent.chen@xxxxxxxxxx > > Cc: Leon Schuermann <leon@is.currently.online> > > Cc: Bart Van Assche <bvanassche@xxxxxxx> > > Reported-by: Kevin Wolf <kwolf@xxxxxxxxxx> > > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > > --- > > Kevin, > > Please test this version, thanks! > > The NBD errors seem to go away with this. > > I'm not sure about side effects, though. Isn't the idea behind EINTR > that you return to userspace to let it handle a signal? Looping in the Well, the retry can be done in one work function, then userspace can get chance to handle signal. > kernel doesn't quite achieve this, so do we delay/prevent signal > delivery with this? On the other hand, if it were completely prevented, > then this should become an infinite loop, which it didn't in my test. If retry can't succeed in the request's deadline, it will fail. > > > drivers/block/nbd.c | 35 +++++++++++++++++++++++++++++++++-- > > 1 file changed, 33 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > > index b852050d8a96..ef84071041e3 100644 > > --- a/drivers/block/nbd.c > > +++ b/drivers/block/nbd.c > > @@ -701,8 +701,9 @@ static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, > > if (sent) { > > nsock->pending = req; > > nsock->sent = sent; > > + } else { > > + set_bit(NBD_CMD_REQUEUED, &cmd->flags); > > } > > - set_bit(NBD_CMD_REQUEUED, &cmd->flags); > > return BLK_STS_RESOURCE; > > } > > dev_err_ratelimited(disk_to_dev(nbd->disk), > > @@ -743,7 +744,6 @@ static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, > > */ > > nsock->pending = req; > > nsock->sent = sent; > > - set_bit(NBD_CMD_REQUEUED, &cmd->flags); > > return BLK_STS_RESOURCE; > > } > > dev_err(disk_to_dev(nbd->disk), > > @@ -778,6 +778,35 @@ static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, > > return BLK_STS_OK; > > } > > > > +/* > > + * Send pending nbd request and payload, part of them have been sent > > + * already, so we have to send them all with current request, and can't > > + * return BLK_STS_RESOURCE, otherwise request tag may be changed in next > > + * retry > > + */ > > +static blk_status_t nbd_send_pending_cmd(struct nbd_device *nbd, > > + struct nbd_cmd *cmd) > > +{ > > + struct request *req = blk_mq_rq_from_pdu(cmd); > > + unsigned long deadline = READ_ONCE(req->deadline); > > + unsigned int wait_ms = 2; > > + blk_status_t res; > > + > > + WARN_ON_ONCE(test_bit(NBD_CMD_REQUEUED, &cmd->flags)); > > + > > + while (true) { > > + res = nbd_send_cmd(nbd, cmd, cmd->index); > > + if (res != BLK_STS_RESOURCE) > > + return res; > > + if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline) > > + break; > > + msleep(wait_ms); > > + wait_ms *= 2; > > + } > > + > > + return BLK_STS_IOERR; > > +} > > + > > static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock, > > struct nbd_reply *reply) > > { > > @@ -1111,6 +1140,8 @@ static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index) > > goto out; > > } > > ret = nbd_send_cmd(nbd, cmd, index); > > + if (ret == BLK_STS_RESOURCE && nsock->pending == req) > > + ret = nbd_send_pending_cmd(nbd, cmd); > > Is there a reason to call nbd_send_cmd() outside of the new loop first > instead of going to the loop directly? It's always better to only have > a single code path. IMO, it is better to add new cold code path for handling the unusual pending request, and nbd_send_cmd() has been too complicated to maintain. Thanks, Ming