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This patch is on top of the previous patch, so should be applied to VZ10 kernel as it is in future releases, or you</div>
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can merge the two patches into one. This patch alone doesn't fix anything, just a refactor of previous patch so that</div>
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it can be backported to VZ9 kernel and release it as a RK. </div>
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<br>
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So both patches address the same bug, RK is needed for VZ9 kernel, you need to backport the 2 patches together </div>
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in order to generate to the RK. you can merge the two patches into one if necessary. </div>
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Regards,</div>
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Liu</div>
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<b>From:</b> Konstantin Khorenko <khorenko@virtuozzo.com><br>
<b>Sent:</b> 29 August 2026 01:13<br>
<b>To:</b> Kui Liu <kui.liu@virtuozzo.com>; devel@openvz.org <devel@openvz.org><br>
<b>Cc:</b> Alexey Kuznetsov <kuznet@virtuozzo.com>; Andrey Zaitsev <azaitsev@virtuozzo.com><br>
<b>Subject:</b> Re: [PATCH VZ10] fs/fuse kio: track pending kRPC connect via state machine only</div>
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<div style="font-size: 11pt;">Liu, please explain what do i do with that patch?<br>
Should i revert ("fs/fuse kio: fix kRPC connect issues") and push this patch instead?<br>
<br>
Should we release it as an RK? If yes - for which kernels and where are the corresponding bugs?<br>
Currently i understand nothing, sorry.<br>
<br>
--<br>
Best regards,<br>
<br>
Konstantin Khorenko,<br>
Virtuozzo Linux Kernel Team<br>
<br>
On 8/27/26 14:37, Liu Kui wrote:<br>
> Rework the previous fix ("fs/fuse kio: fix kRPC connect issues") to not<br>
> require the new struct pcs_krpc member "connect_req", so the fix can be<br>
> shipped as a livepatch.<br>
><br>
> Both things connect_req was tracking are already derivable from the<br>
> existing state machine once PCS_KRPC_STATE_CONNECT is made to mean<br>
> exactly "a connect req is in flight":<br>
><br>
> - krpc_connect_done() settles a failed connect back to UNCONN instead<br>
> of leaving the state in CONNECT forever;<br>
><br>
> - pcs_krpc_abort() no longer resets CONNECT to UNCONN: the req is<br>
> still in flight, and only its completion settles the state;<br>
><br>
> - pcs_krpc_connect() proceeds only from UNCONN or ABORTED, refusing<br>
> new connects (-EPERM) while a req is in flight - at most one connect<br>
> req exists at a time, same as with the connect_req check;<br>
><br>
> - pcs_krpc_poll() reports EPOLLERR on UNCONN: poll bails out earlier<br>
> unless ctx->gen == krpc->gen, and the current session can only be in<br>
> UNCONN if its connect failed or was aborted, which is what the<br>
> (CONNECT && !connect_req) test used to detect.<br>
><br>
> gen only advances in pcs_krpc_connect(), which is blocked during<br>
> CONNECT, so within that state the in-flight req always carries the<br>
> current gen and krpc_connect_done()'s existing staleness check is<br>
> sufficient.<br>
><br>
> Related to:<br>
> <a href="https://virtuozzo.atlassian.net/browse/VSTOR-135626" id="OWA1ab633ca-1994-eb4c-a86a-7726e8185a2b" class="OWAAutoLink" data-auth="NotApplicable">
https://virtuozzo.atlassian.net/browse/VSTOR-135626</a><br>
><br>
> Signed-off-by: Liu Kui <kui.liu@virtuozzo.com><br>
> ---<br>
> fs/fuse/kio/pcs/pcs_krpc.c | 39 ++++++++++++++++++++++++++++----------<br>
> fs/fuse/kio/pcs/pcs_krpc.h | 2 --<br>
> 2 files changed, 29 insertions(+), 12 deletions(-)<br>
><br>
> diff --git a/fs/fuse/kio/pcs/pcs_krpc.c b/fs/fuse/kio/pcs/pcs_krpc.c<br>
> index b55c093c13d0..bcfbfc6d9304 100644<br>
> --- a/fs/fuse/kio/pcs/pcs_krpc.c<br>
> +++ b/fs/fuse/kio/pcs/pcs_krpc.c<br>
> @@ -738,8 +738,12 @@ static int pcs_krpc_abort(struct pcs_krpc *krpc)<br>
> spin_lock(&krpc->lock);<br>
> <br>
> if (krpc->state != PCS_KRPC_STATE_CONNECTED) {<br>
> - if (krpc->state == PCS_KRPC_STATE_CONNECT)<br>
> - krpc->state = PCS_KRPC_STATE_UNCONN;<br>
> + /*<br>
> + * A pending connect stays in CONNECT state: its connect req<br>
> + * is still in flight and krpc_connect_done() will settle the<br>
> + * state to UNCONN when it completes. Until then new connects<br>
> + * are refused, so at most one connect req exists at a time.<br>
> + */<br>
> spin_unlock(&krpc->lock);<br>
> return 0;<br>
> }<br>
> @@ -907,8 +911,13 @@ static __poll_t pcs_krpc_poll(struct file *file, poll_table *wait)<br>
> <br>
> spin_lock(&krpc->lock);<br>
> <br>
> + /*<br>
> + * ctx->gen == krpc->gen (checked above) means this is the current<br>
> + * session, so UNCONN here can only mean its connect attempt has<br>
> + * failed (see krpc_connect_done()) or the session was aborted.<br>
> + */<br>
> if (krpc->state == PCS_KRPC_STATE_ABORTED ||<br>
> - (krpc->state == PCS_KRPC_STATE_CONNECT && !krpc->connect_req)) {<br>
> + krpc->state == PCS_KRPC_STATE_UNCONN) {<br>
> pollflags |= EPOLLERR;<br>
> } else if (krpc->state == PCS_KRPC_STATE_CONNECTED) {<br>
> pollflags |= EPOLLOUT;<br>
> @@ -999,7 +1008,6 @@ int pcs_krpc_create(struct pcs_krpc_set *krpcs, PCS_NODE_ID_T *id,<br>
> krpc->gen = 0;<br>
> krpc->state = PCS_KRPC_STATE_UNCONN;<br>
> krpc->cs = NULL;<br>
> - krpc->connect_req = NULL;<br>
> <br>
> krpc->rpc = pcs_rpc_clnt_create(&cc_from_krpcset(krpcs)->eng, id, addr, cs_flags);<br>
> if (!krpc->rpc) {<br>
> @@ -1051,8 +1059,6 @@ static void krpc_connect_done(struct pcs_msg *msg)<br>
> }<br>
> <br>
> spin_lock(&krpc->lock);<br>
> - if (krpc->connect_req == req)<br>
> - krpc->connect_req = NULL;<br>
> /* from a stale session, do nothing */<br>
> if (req->gen != krpc->gen || krpc->state != PCS_KRPC_STATE_CONNECT) {<br>
> spin_unlock(&krpc->lock);<br>
> @@ -1062,6 +1068,14 @@ static void krpc_connect_done(struct pcs_msg *msg)<br>
> if (!pcs_if_error(&msg->error)) {<br>
> krpc->state = PCS_KRPC_STATE_CONNECTED;<br>
> pollflags = EPOLLOUT;<br>
> + } else {<br>
> + /*<br>
> + * Connect failed: settle back to UNCONN so that a new connect<br>
> + * is allowed again, and report the failure to poll(). Since<br>
> + * gen is unchanged, the current session's poll sees UNCONN<br>
> + * and returns EPOLLERR.<br>
> + */<br>
> + krpc->state = PCS_KRPC_STATE_UNCONN;<br>
> }<br>
> spin_unlock(&krpc->lock);<br>
> <br>
> @@ -1119,9 +1133,15 @@ int pcs_krpc_connect(struct pcs_krpc_set *krpcs, PCS_NODE_ID_T *id)<br>
> }<br>
> <br>
> spin_lock(&krpc->lock);<br>
> - if (krpc->state == PCS_KRPC_STATE_CONNECTED ||<br>
> - krpc->state == PCS_KRPC_STATE_DESTROYED ||<br>
> - krpc->connect_req) {<br>
> + /*<br>
> + * A connect is allowed only when there is neither an established<br>
> + * session nor a connect req in flight (CONNECT state, see<br>
> + * krpc_connect_done()). This limits connect reqs to one at a time:<br>
> + * if userspace gave up on a connect and retries, the new connect<br>
> + * fails immediately until the old req completes.<br>
> + */<br>
> + if (krpc->state != PCS_KRPC_STATE_UNCONN &&<br>
> + krpc->state != PCS_KRPC_STATE_ABORTED) {<br>
> spin_unlock(&krpc->lock);<br>
> err = -EPERM;<br>
> /* fput() drops ctx and its krpc reference via pcs_krpc_release() */<br>
> @@ -1133,7 +1153,6 @@ int pcs_krpc_connect(struct pcs_krpc_set *krpcs, PCS_NODE_ID_T *id)<br>
> connect_req->gen = krpc->gen;<br>
> connect_req->krpc = pcs_krpc_get(krpc);<br>
> krpc->state = PCS_KRPC_STATE_CONNECT;<br>
> - krpc->connect_req = connect_req;<br>
> spin_unlock(&krpc->lock);<br>
> <br>
> /* publish the fd only after the connect is committed */<br>
> diff --git a/fs/fuse/kio/pcs/pcs_krpc.h b/fs/fuse/kio/pcs/pcs_krpc.h<br>
> index 3db9e9712019..6a090ef66185 100644<br>
> --- a/fs/fuse/kio/pcs/pcs_krpc.h<br>
> +++ b/fs/fuse/kio/pcs/pcs_krpc.h<br>
> @@ -82,8 +82,6 @@ struct pcs_krpc {<br>
> /** Wait queue head for poll */<br>
> wait_queue_head_t poll_wait;<br>
> struct pcs_cs *cs;<br>
> -<br>
> - struct krpc_connect_req *connect_req;<br>
> };<br>
> <br>
> struct pcs_krpc_context {<br>
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