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Message-ID: <0da7d896-0d67-46f6-83f9-b346eba991a9@gmail.com>
Date: Mon, 17 Dec 2018 08:37:57 +0100
From: Tomas Bortoli <tomasbortoli@...il.com>
To: Dominique Martinet <asmadeus@...ewreck.org>,
v9fs-developer@...ts.sourceforge.net
Cc: Dominique Martinet <dominique.martinet@....fr>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Eric Van Hensbergen <ericvh@...il.com>,
Latchesar Ionkov <lucho@...kov.net>,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH 1/3] 9p/net: implement asynchronous rpc
Hey Dominique,
sorry for the delay, I've been quite busy these days.
The patches looks good to me and should indeed speed up the code a bit.
I quickly tested them against Syzkaller tuned for the 9p subsystem and
everything seems fine.
And by the way, which refcount races?
Cheers,
Tomas
On 12/11/18 1:41 PM, Dominique Martinet wrote:
> From: Dominique Martinet <dominique.martinet@....fr>
>
> Add p9_client_async_rpc that will let us send an rpc without waiting
> for the reply, as well as an async handler hook.
>
> The work done in the hook could mostly be done in the client callback,
> but I prefered not to for a couple of reasons:
> - the callback can be called in an IRQ for some transports, and the
> handler needs to call p9_tag_remove which takes the client lock that has
> recently been reworked to not be irq-compatible (as it was never taken
> in IRQs until now)
> - the handled replies can be handled anytime, there is nothing the
> userspace would care about and want to be notified of quickly
> - the async request list and this function would be needed anyway for
> when we disconnect the client, in order to not leak async requests that
> haven't been replied to
>
> Signed-off-by: Dominique Martinet <dominique.martinet@....fr>
> Cc: Eric Van Hensbergen <ericvh@...il.com>
> Cc: Latchesar Ionkov <lucho@...kov.net>
> Cc: Tomas Bortoli <tomasbortoli@...il.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> ---
>
> I've been sitting on these patches for almost a month now because I
> wanted to fix the cancel race, but I think it's what the most recent
> syzbot email is about so if it could find it without this it probably
> won't hurt to at least get some reviews for these three patches first.
>
> I won't submit these for next cycle, so will only put them into -next
> after 4.20 is released; hopefully I'll have time to look at the two
> pending refcount races around that time.
> Until then, comments please!
>
>
> include/net/9p/client.h | 9 +++++-
> net/9p/client.c | 64 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 72 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/9p/client.h b/include/net/9p/client.h
> index 947a570307a6..a4ded7666c73 100644
> --- a/include/net/9p/client.h
> +++ b/include/net/9p/client.h
> @@ -89,7 +89,8 @@ enum p9_req_status_t {
> * @tc: the request fcall structure
> * @rc: the response fcall structure
> * @aux: transport specific data (provided for trans_fd migration)
> - * @req_list: link for higher level objects to chain requests
> + * @req_list: link used by trans_fd
> + * @async_list: link used to check on async requests
> */
> struct p9_req_t {
> int status;
> @@ -100,6 +101,7 @@ struct p9_req_t {
> struct p9_fcall rc;
> void *aux;
> struct list_head req_list;
> + struct list_head async_list;
> };
>
> /**
> @@ -110,6 +112,9 @@ struct p9_req_t {
> * @trans_mod: module API instantiated with this client
> * @status: connection state
> * @trans: tranport instance state and API
> + * @fcall_cache: kmem cache for client request data (msize-specific)
> + * @async_req_lock: protects @async_req_list
> + * @async_req_list: list of requests waiting a reply
> * @fids: All active FID handles
> * @reqs: All active requests.
> * @name: node name used as client id
> @@ -125,6 +130,8 @@ struct p9_client {
> enum p9_trans_status status;
> void *trans;
> struct kmem_cache *fcall_cache;
> + spinlock_t async_req_lock;
> + struct list_head async_req_list;
>
> union {
> struct {
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 357214a51f13..0a67c3ccd4fd 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -729,6 +729,62 @@ static struct p9_req_t *p9_client_prepare_req(struct p9_client *c,
> return ERR_PTR(err);
> }
>
> +static struct p9_req_t *
> +p9_client_async_rpc(struct p9_client *c, int8_t type, const char *fmt, ...)
> +{
> + va_list ap;
> + int err;
> + struct p9_req_t *req;
> +
> + va_start(ap, fmt);
> + req = p9_client_prepare_req(c, type, c->msize, fmt, ap);
> + va_end(ap);
> + if (IS_ERR(req))
> + return req;
> +
> + err = c->trans_mod->request(c, req);
> + if (err < 0) {
> + /* bail out without flushing... */
> + p9_req_put(req);
> + p9_tag_remove(c, req);
> + if (err != -ERESTARTSYS && err != -EFAULT)
> + c->status = Disconnected;
> + return ERR_PTR(safe_errno(err));
> + }
> +
> + return req;
> +}
> +
> +static void p9_client_handle_async(struct p9_client *c, bool free_all)
> +{
> + struct p9_req_t *req, *nreq;
> +
> + /* it's ok to miss some async replies here, do a quick check without
> + * lock first unless called with free_all
> + */
> + if (!free_all && list_empty(&c->async_req_list))
> + return;
> +
> + spin_lock_irq(&c->async_req_lock);
> + list_for_each_entry_safe(req, nreq, &c->async_req_list, async_list) {
> + if (free_all && req->status < REQ_STATUS_RCVD) {
> + p9_debug(P9_DEBUG_ERROR,
> + "final async handler found req tag %d type %d status %d\n",
> + req->tc.tag, req->tc.id, req->status);
> + if (c->trans_mod->cancelled)
> + c->trans_mod->cancelled(c, req);
> + /* won't receive reply now */
> + p9_req_put(req);
> + }
> + if (free_all || req->status >= REQ_STATUS_RCVD) {
> + /* Put old refs whatever reqs actually returned */
> + list_del(&req->async_list);
> + p9_tag_remove(c, req);
> + }
> + }
> + spin_unlock_irq(&c->async_req_lock);
> +}
> +
> /**
> * p9_client_rpc - issue a request and wait for a response
> * @c: client session
> @@ -746,6 +802,8 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...)
> unsigned long flags;
> struct p9_req_t *req;
>
> + p9_client_handle_async(c, 0);
> +
> va_start(ap, fmt);
> req = p9_client_prepare_req(c, type, c->msize, fmt, ap);
> va_end(ap);
> @@ -841,6 +899,8 @@ static struct p9_req_t *p9_client_zc_rpc(struct p9_client *c, int8_t type,
> unsigned long flags;
> struct p9_req_t *req;
>
> + p9_client_handle_async(c, 0);
> +
> va_start(ap, fmt);
> /*
> * We allocate a inline protocol data of only 4k bytes.
> @@ -1030,6 +1090,8 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
> memcpy(clnt->name, client_id, strlen(client_id) + 1);
>
> spin_lock_init(&clnt->lock);
> + spin_lock_init(&clnt->async_req_lock);
> + INIT_LIST_HEAD(&clnt->async_req_list);
> idr_init(&clnt->fids);
> idr_init(&clnt->reqs);
>
> @@ -1101,6 +1163,8 @@ void p9_client_destroy(struct p9_client *clnt)
>
> v9fs_put_trans(clnt->trans_mod);
>
> + p9_client_handle_async(clnt, 1);
> +
> idr_for_each_entry(&clnt->fids, fid, id) {
> pr_info("Found fid %d not clunked\n", fid->fid);
> p9_fid_destroy(fid);
>
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