Re: [PATCH v3 3/6] nbd: remove queue freeze in nbd_add_socket

[yangerkun <yangerkun@huawei.com>]

在 2026/7/22 16:45, yangerkun 写道:
> 在 2026/7/22 14:35, yu kuai 写道:
> > Hi,
> >
> > 在 2026/7/22 11:17, yu kuai 写道:
> > > Hi,
> > >
> > > 在 2026/7/13 14:56, Yang Erkun 写道:
> > > > nbd_add_socket can never run concurrently with inflight I/O:
> > > >
> > > >     - netlink path: nbd_genl_connect calls nbd_add_socket before
> > > >       nbd_start_device, so no I/O can happened when invoking 
> > > > nbd_add_socket,
> > > >       nbd_genl_reconfigure cannot too since it won't call 
> > > > nbd_add_socket
> > > >
> > > >     - ioctl path: NBD_SET_SOCK cannot be called after NBD_DO_IT with
> > > >       the previous commit, so capability of nbd will keep 0 while
> > > >       invoking NBD_SET_SOCK
> > > >
> > > > Removing the freeze in nbd_add_socket to speed up nbd device startup.
> > > Check nbd_open(), the pid is not checked there, which means the nbd 
> > > device
> > > can be opened after add_disk() succeed. Normally read/write IO will 
> > > not pass
> > > bio_check_eod() checking, however, there can be special zero sized 
> > > bio that
> > > might still be issued to nbd device. So I think there should be a pid 
> > > checking
> > > in nbd_open() for this patch, and I'm not aware of any special IO 
> > > mush be handled
> > > before nbd_start_device(). Otherwise, the freeze is still necessary 
> > > since
> > > nbd_handle_cmd() will deference config->socks[] directly.
> >
> > Sorry this is a mistake, nbd_open() must succeed before pid is set, 
> > because of ioctl
> > like NBD_SET_SOCK and NED_DO_IT :( I just forgot this simple case.
>
> nbd can only accept request from bio, so bio_check_eod will reject them 
> all?

Sorry, for read/write bio, bio_check_eod will reject them, for flush 
only bio, if (!bdev_write_cache(bdev)) in submit_bio_noacct will reject 
it. So it seems safe here.

> > > > Signed-off-by: Yang Erkun <yangerkun@huawei.com>
> > > > ---
> > > >     drivers/block/nbd.c | 9 ---------
> > > >     1 file changed, 9 deletions(-)
> > > >
> > > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > > > index a15553ab4b97..0755b7046ed4 100644
> > > > --- a/drivers/block/nbd.c
> > > > +++ b/drivers/block/nbd.c
> > > > @@ -1272,7 +1272,6 @@ static int nbd_add_socket(struct nbd_device 
> > > > *nbd, unsigned long arg,
> > > >         struct socket *sock;
> > > >         struct nbd_sock **socks;
> > > >         struct nbd_sock *nsock;
> > > > -    unsigned int memflags;
> > > >         int err;
> > > >         /* Arg will be cast to int, check it to avoid overflow */
> > > > @@ -1283,12 +1282,6 @@ static int nbd_add_socket(struct nbd_device 
> > > > *nbd, unsigned long arg,
> > > >             return err;
> > > >         nbd_reclassify_socket(sock);
> > > > -    /*
> > > > -     * We need to make sure we don't get any errant requests while 
> > > > we're
> > > > -     * reallocating the ->socks array.
> > > > -     */
> > > > -    memflags = blk_mq_freeze_queue(nbd->disk->queue);
> > > > -
> > > >         if (!netlink && !nbd->task_setup &&
> > > >             !test_bit(NBD_RT_BOUND, &config->runtime_flags))
> > > >             nbd->task_setup = current;
> > > > @@ -1335,12 +1328,10 @@ static int nbd_add_socket(struct nbd_device 
> > > > *nbd, unsigned long arg,
> > > >         INIT_WORK(&nsock->work, nbd_pending_cmd_work);
> > > >         socks[config->num_connections++] = nsock;
> > > >         atomic_inc(&config->live_connections);
> > > > -    blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
> > > >         return 0;
> > > >     put_socket:
> > > > -    blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
> > > >         sockfd_put(sock);
> > > >         return err;
> > > >     }