Fix the interruptibility of kernel-initiated client calls so that they're
either only interruptible when they're waiting for a call slot to come
available or they're not interruptible at all.  Either way, they're not
interruptible during transmission.

This should help prevent StoreData calls from being interrupted when
writeback is in progress.  It doesn't, however, handle interruption during
the receive phase.

Userspace-initiated calls are still interruptable.  After the signal has
been handled, sendmsg() will return the amount of data copied out of the
buffer and userspace can perform another sendmsg() call to continue
transmission.

Fixes: bc5e3a54 ("rxrpc: Use MSG_WAITALL to tell sendmsg() to temporarily ignore signals")
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Abstract out the calculation of there being sufficient Tx buffer space.
This is reproduced several times in the rxrpc sendmsg code.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Fix the cleanup of the crypto state on a call after the call has been
disconnected.  As the call has been disconnected, its connection ref has
been discarded and so we can't go through that to get to the security ops
table.

Fix this by caching the security ops pointer in the rxrpc_call struct and
using that when freeing the call security state.  Also use this in other
places we're dealing with call-specific security.

The symptoms look like:

    BUG: KASAN: use-after-free in rxrpc_release_call+0xb2d/0xb60
    net/rxrpc/call_object.c:481
    Read of size 8 at addr ffff888062ffeb50 by task syz-executor.5/4764

Fixes: 1db88c53 ("rxrpc: Fix -Wframe-larger-than= warnings from on-stack crypto")
Reported-by: syzbot+eed305768ece6682bb7f@syzkaller.appspotmail.com
Signed-off-by: NDavid Howells <dhowells@redhat.com>

When sendmsg() finds a call to continue on with, if the call is in an
inappropriate state, it doesn't release the ref it just got on that call
before returning an error.

This causes the following symptom to show up with kasan:

	BUG: KASAN: use-after-free in rxrpc_send_keepalive+0x8a2/0x940
	net/rxrpc/output.c:635
	Read of size 8 at addr ffff888064219698 by task kworker/0:3/11077

where line 635 is:

	whdr.epoch	= htonl(peer->local->rxnet->epoch);

The local endpoint (which cannot be pinned by the call) has been released,
but not the peer (which is pinned by the call).

Fix this by releasing the call in the error path.

Fixes: 37411cad ("rxrpc: Fix potential NULL-pointer exception")
Reported-by: syzbot+d850c266e3df14da1d31@syzkaller.appspotmail.com
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Use the previously-added transmit-phase skbuff private flag to simplify the
socket buffer tracing a bit.  Which phase the skbuff comes from can now be
divined from the skb rather than having to be guessed from the call state.

We can also reduce the number of rxrpc_skb_trace values by eliminating the
difference between Tx and Rx in the symbols.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

    
Add a flag in the private data on an skbuff to indicate that this is a
transmission-phase buffer rather than a receive-phase buffer.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Fix the fact that a notification isn't sent to the recvmsg side to indicate
a call failed when sendmsg() fails to transmit a DATA packet with the error
ENETUNREACH, EHOSTUNREACH or ECONNREFUSED.

Without this notification, the afs client just sits there waiting for the
call to complete in some manner (which it's not now going to do), which
also pins the rxrpc call in place.

This can be seen if the client has a scope-level IPv6 address, but not a
global-level IPv6 address, and we try and transmit an operation to a
server's IPv6 address.

Looking in /proc/net/rxrpc/calls shows completed calls just sat there with
an abort code of RX_USER_ABORT and an error code of -ENETUNREACH.

Fixes: c54e43d7 ("rxrpc: Fix missing start of call timeout")
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Reviewed-by: NMarc Dionne <marc.dionne@auristor.com>
Reviewed-by: NJeffrey Altman <jaltman@auristor.com>

Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public licence as published by
  the free software foundation either version 2 of the licence or at
  your option any later version

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 114 file(s).
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NAllison Randal <allison@lohutok.net>
Reviewed-by: NKate Stewart <kstewart@linuxfoundation.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190520170857.552531963@linutronix.deSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Allow kernel services using AF_RXRPC to indicate that a call should be
non-interruptible.  This allows kafs to make things like lock-extension and
writeback data storage calls non-interruptible.

If this is set, signals will be ignored for operations on that call where
possible - such as waiting to get a call channel on an rxrpc connection.

It doesn't prevent UDP sendmsg from being interrupted, but that will be
handled by packet retransmission.

rxrpc_kernel_recv_data() isn't affected by this since that never waits,
preferring instead to return -EAGAIN and leave the waiting to the caller.

Userspace initiated calls can't be set to be uninterruptible at this time.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Change rxrpc_queue_packet()'s signature so that it can return any error
code it may encounter when trying to send the packet.

This allows the caller to eventually do something in case of error - though
it should be noted that the packet has been queued and a resend is
scheduled.
Signed-off-by: NMarc Dionne <marc.dionne@auristor.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The changes introduced to allow rxrpc calls to be retried creates an issue
when it comes to refcounting afs_call structs.  The problem is that when
rxrpc_send_data() queues the last packet for an asynchronous call, the
following sequence can occur:

 (1) The notify_end_tx callback is invoked which causes the state in the
     afs_call to be changed from AFS_CALL_CL_REQUESTING or
     AFS_CALL_SV_REPLYING.

 (2) afs_deliver_to_call() can then process event notifications from rxrpc
     on the async_work queue.

 (3) Delivery of events, such as an abort from the server, can cause the
     afs_call state to be changed to AFS_CALL_COMPLETE on async_work.

 (4) For an asynchronous call, afs_process_async_call() notes that the call
     is complete and tried to clean up all the refs on async_work.

 (5) rxrpc_send_data() might return the amount of data transferred
     (success) or an error - which could in turn reflect a local error or a
     received error.

Synchronising the clean up after rxrpc_kernel_send_data() returns an error
with the asynchronous cleanup is then tricky to get right.

Mostly revert commit c038a58c.  The two API
functions the original commit added aren't currently used.  This makes
rxrpc_kernel_send_data() always return successfully if it queued the data
it was given.

Note that this doesn't affect synchronous calls since their Rx notification
function merely pokes a wait queue and does not refcounting.  The
asynchronous call notification function *has* to do refcounting and pass a
ref over the work item to avoid the need to sync the workqueue in call
cleanup.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The expect_rx_by call timeout is supposed to be set when a call is started
to indicate that we need to receive a packet by that point.  This is
currently put back every time we receive a packet, but it isn't started
when we first send a packet.  Without this, the call may wait forever if
the server doesn't deign to reply.

Fix this by setting the timeout upon a successful UDP sendmsg call for the
first DATA packet.  The timeout is initiated only for initial transmission
and not for subsequent retries as we don't want the retry mechanism to
extend the timeout indefinitely.

Fixes: a158bdd3 ("rxrpc: Fix call timeouts")
Reported-by: NMarc Dionne <marc.dionne@auristor.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>

When a new client call is requested, an rxrpc_conn_parameters struct object
is passed in with a bunch of parameters set, such as the local endpoint to
use.  A pointer to the target peer record is also placed in there by
rxrpc_get_client_conn() - and this is removed if and only if a new
connection object is allocated.  Thus it leaks if a new connection object
isn't allocated.

Fix this by putting any peer object attached to the rxrpc_conn_parameters
object in the function that allocated it.

Fixes: 19ffa01c ("rxrpc: Use structs to hold connection params and protocol info")
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Fix various issues detected by checker.

Errors:

 (*) rxrpc_discard_prealloc() should be using rcu_assign_pointer to set
     call->socket.

Warnings:

 (*) rxrpc_service_connection_reaper() should be passing NULL rather than 0 to
     trace_rxrpc_conn() as the where argument.

 (*) rxrpc_disconnect_client_call() should get its net pointer via the
     call->conn rather than call->sock to avoid a warning about accessing
     an RCU pointer without protection.

 (*) Proc seq start/stop functions need annotation as they pass locks
     between the functions.

False positives:

 (*) Checker doesn't correctly handle of seq-retry lock context balance in
     rxrpc_find_service_conn_rcu().

 (*) Checker thinks execution may proceed past the BUG() in
     rxrpc_publish_service_conn().

 (*) Variable length array warnings from SKCIPHER_REQUEST_ON_STACK() in
     rxkad.c.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

rxrpc calls have a ring of packets that are awaiting ACK or retransmission
and a parallel ring of annotations that tracks the state of those packets.
If the initial transmission of a packet on the underlying UDP socket fails
then the packet annotation is marked for resend - but the setting of this
mark accidentally erases the last-packet mark also stored in the same
annotation slot.  If this happens, a call won't switch out of the Tx phase
when all the packets have been transmitted.

Fix this by retaining the last-packet mark and only altering the packet
state.

Fixes: 248f219c ("rxrpc: Rewrite the data and ack handling code")
Signed-off-by: NDavid Howells <dhowells@redhat.com>

In rxrpc and afs, use the debug_ids that are monotonically allocated to
various objects as they're allocated rather than pointers as kernel
pointers are now hashed making them less useful.  Further, the debug ids
aren't reused anywhere nearly as quickly.

In addition, allow kernel services that use rxrpc, such as afs, to take
numbers from the rxrpc counter, assign them to their own call struct and
pass them in to rxrpc for both client and service calls so that the trace
lines for each will have the same ID tag.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Values assigned to both variable resend_at and ack_at are overwritten
before they can be used.

The correct fix here is to add 'now' to the previously computed value in
resend_at and ack_at.

Addresses-Coverity-ID: 1462262
Addresses-Coverity-ID: 1462263
Addresses-Coverity-ID: 1462264
Fixes: beb8e5e4 ("rxrpc: Express protocol timeouts in terms of RTT")
Link: https://marc.info/?i=17004.1511808959%40warthog.procyon.org.ukSigned-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Add an extra timeout that is set/updated when we send a DATA packet that
has the request-ack flag set.  This allows us to detect if we don't get an
ACK in response to the latest flagged packet.

The ACK packet is adjudged to have been lost if it doesn't turn up within
2*RTT of the transmission.

If the timeout occurs, we schedule the sending of a PING ACK to find out
the state of the other side.  If a new DATA packet is ready to go sooner,
we cancel the sending of the ping and set the request-ack flag on that
instead.

If we get back a PING-RESPONSE ACK that indicates a lower tx_top than what
we had at the time of the ping transmission, we adjudge all the DATA
packets sent between the response tx_top and the ping-time tx_top to have
been lost and retransmit immediately.

Rather than sending a PING ACK, we could just pick a DATA packet and
speculatively retransmit that with request-ack set.  It should result in
either a REQUESTED ACK or a DUPLICATE ACK which we can then use in lieu the
a PING-RESPONSE ACK mentioned above.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Express protocol timeouts for data retransmission and deferred ack
generation in terms on RTT rather than specified timeouts once we have
sufficient RTT samples.

For the moment, this requires just one RTT sample to be able to use this
for ack deferral and two for data retransmission.

The data retransmission timeout is set at RTT*1.5 and the ACK deferral
timeout is set at RTT.

Note that the calculated timeout is limited to a minimum of 4ns to make
sure it doesn't happen too quickly.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Fix the rxrpc call expiration timeouts and make them settable from
userspace.  By analogy with other rx implementations, there should be three
timeouts:

 (1) "Normal timeout"

     This is set for all calls and is triggered if we haven't received any
     packets from the peer in a while.  It is measured from the last time
     we received any packet on that call.  This is not reset by any
     connection packets (such as CHALLENGE/RESPONSE packets).

     If a service operation takes a long time, the server should generate
     PING ACKs at a duration that's substantially less than the normal
     timeout so is to keep both sides alive.  This is set at 1/6 of normal
     timeout.

 (2) "Idle timeout"

     This is set only for a service call and is triggered if we stop
     receiving the DATA packets that comprise the request data.  It is
     measured from the last time we received a DATA packet.

 (3) "Hard timeout"

     This can be set for a call and specified the maximum lifetime of that
     call.  It should not be specified by default.  Some operations (such
     as volume transfer) take a long time.

Allow userspace to set/change the timeouts on a call with sendmsg, using a
control message:

	RXRPC_SET_CALL_TIMEOUTS

The data to the message is a number of 32-bit words, not all of which need
be given:

	u32 hard_timeout;	/* sec from first packet */
	u32 idle_timeout;	/* msec from packet Rx */
	u32 normal_timeout;	/* msec from data Rx */

This can be set in combination with any other sendmsg() that affects a
call.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

When rxrpc_sendmsg() parses the control message buffer, it places the
parameters extracted into a structure, but lumps together call parameters
(such as user call ID) with operation parameters (such as whether to send
data, send an abort or accept a call).

Split the call parameters out into their own structure, a copy of which is
then embedded in the operation parameters struct.

The call parameters struct is then passed down into the places that need it
instead of passing the individual parameters.  This allows for extra call
parameters to be added.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Don't set upgrade by default when creating a call from sendmsg().  This is
a holdover from when I was testing the code.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

The caller of rxrpc_accept_call() must release the lock on call->user_mutex
returned by that function.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Make AF_RXRPC accept MSG_WAITALL as a flag to sendmsg() to tell it to
ignore signals whilst loading up the message queue, provided progress is
being made in emptying the queue at the other side.

Progress is defined as the base of the transmit window having being
advanced within 2 RTT periods.  If the period is exceeded with no progress,
sendmsg() will return anyway, indicating how much data has been copied, if
any.

Once the supplied buffer is entirely decanted, the sendmsg() will return.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Allow a client call that failed on network error to be retried, provided
that the Tx queue still holds DATA packet 1.  This allows an operation to
be submitted to another server or another address for the same server
without having to repackage and re-encrypt the data so far processed.

Two new functions are provided:

 (1) rxrpc_kernel_check_call() - This is used to find out the completion
     state of a call to guess whether it can be retried and whether it
     should be retried.

 (2) rxrpc_kernel_retry_call() - Disconnect the call from its current
     connection, reset the state and submit it as a new client call to a
     new address.  The new address need not match the previous address.

A call may be retried even if all the data hasn't been loaded into it yet;
a partially constructed will be retained at the same point it was at when
an error condition was detected.  msg_data_left() can be used to find out
how much data was packaged before the error occurred.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Add a callback to rxrpc_kernel_send_data() so that a kernel service can get
a notification that the AF_RXRPC call has transitioned out the Tx phase and
is now waiting for a reply or a final ACK.

This is called from AF_RXRPC with the call state lock held so the
notification is guaranteed to come before any reply is passed back.

Further, modify the AFS filesystem to make use of this so that we don't have
to change the afs_call state before sending the last bit of data.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

call->error is stored as 0 or a negative error code.  Don't negate this
value (ie. make it positive) before returning it from a kernel function
(though it should still be negated before passing to userspace through a
control message).
Signed-off-by: NDavid Howells <dhowells@redhat.com>

There were many places that my previous spatch didn't find,
as pointed out by yuan linyu in various patches.

The following spatch found many more and also removes the
now unnecessary casts:

    @@
    identifier p, p2;
    expression len;
    expression skb;
    type t, t2;
    @@
    (
    -p = skb_put(skb, len);
    +p = skb_put_zero(skb, len);
    |
    -p = (t)skb_put(skb, len);
    +p = skb_put_zero(skb, len);
    )
    ... when != p
    (
    p2 = (t2)p;
    -memset(p2, 0, len);
    |
    -memset(p, 0, len);
    )

    @@
    type t, t2;
    identifier p, p2;
    expression skb;
    @@
    t *p;
    ...
    (
    -p = skb_put(skb, sizeof(t));
    +p = skb_put_zero(skb, sizeof(t));
    |
    -p = (t *)skb_put(skb, sizeof(t));
    +p = skb_put_zero(skb, sizeof(t));
    )
    ... when != p
    (
    p2 = (t2)p;
    -memset(p2, 0, sizeof(*p));
    |
    -memset(p, 0, sizeof(*p));
    )

    @@
    expression skb, len;
    @@
    -memset(skb_put(skb, len), 0, len);
    +skb_put_zero(skb, len);

Apply it to the tree (with one manual fixup to keep the
comment in vxlan.c, which spatch removed.)
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Provide a control message that can be specified on the first sendmsg() of a
client call or the first sendmsg() of a service response to indicate the
total length of the data to be transmitted for that call.

Currently, because the length of the payload of an encrypted DATA packet is
encrypted in front of the data, the packet cannot be encrypted until we
know how much data it will hold.

By specifying the length at the beginning of the transmit phase, each DATA
packet length can be set before we start loading data from userspace (where
several sendmsg() calls may contribute to a particular packet).

An error will be returned if too little or too much data is presented in
the Tx phase.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Consolidate the sendmsg control message parameters into a struct rather
than passing them individually through the argument list of
rxrpc_sendmsg_cmsg().  This makes it easier to add more parameters.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Make it possible for a client to use AuriStor's service upgrade facility.

The client does this by adding an RXRPC_UPGRADE_SERVICE control message to
the first sendmsg() of a call.  This takes no parameters.

When recvmsg() starts returning data from the call, the service ID field in
the returned msg_name will reflect the result of the upgrade attempt.  If
the upgrade was ignored, srx_service will match what was set in the
sendmsg(); if the upgrade happened the srx_service will be altered to
indicate the service the server upgraded to.

Note that:

 (1) The choice of upgrade service is up to the server

 (2) Further client calls to the same server that would share a connection
     are blocked if an upgrade probe is in progress.

 (3) This should only be used to probe the service.  Clients should then
     use the returned service ID in all subsequent communications with that
     server (and not set the upgrade).  Note that the kernel will not
     retain this information should the connection expire from its cache.

 (4) If a server that supports upgrading is replaced by one that doesn't,
     whilst a connection is live, and if the replacement is running, say,
     OpenAFS 1.6.4 or older or an older IBM AFS, then the replacement
     server will not respond to packets sent to the upgraded connection.

     At this point, calls will time out and the server must be reprobed.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Add a tracepoint (rxrpc_rx_proto) to record protocol errors in received
packets.  The following changes are made:

 (1) Add a function, __rxrpc_abort_eproto(), to note a protocol error on a
     call and mark the call aborted.  This is wrapped by
     rxrpc_abort_eproto() that makes the why string usable in trace.

 (2) Add trace_rxrpc_rx_proto() or rxrpc_abort_eproto() to protocol error
     generation points, replacing rxrpc_abort_call() with the latter.

 (3) Only send an abort packet in rxkad_verify_packet*() if we actually
     managed to abort the call.

Note that a trace event is also emitted if a kernel user (e.g. afs) tries
to send data through a call when it's not in the transmission phase, though
it's not technically a receive event.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Make rxrpc_kernel_abort_call() return an indication as to whether it
actually aborted the operation or not so that kafs can trace the failure of
the operation.  Note that 'success' in this context means changing the
state of the call, not necessarily successfully transmitting an ABORT
packet.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Use negative error codes in struct rxrpc_call::error because that's what
the kernel normally deals with and to make the code consistent.  We only
turn them positive when transcribing into a cmsg for userspace recvmsg.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

If rxrpc_kernel_send_data() is asked to send data through a call that has
already failed (due to a remote abort, received protocol error or network
error), then return the associated error code saved in the call rather than
ESHUTDOWN.

This allows the caller to work out whether to ask for the abort code or not
based on this.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The call state may be changed at any time by the data-ready routine in
response to received packets, so if the call state is to be read and acted
upon several times in a function, READ_ONCE() must be used unless the call
state lock is held.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Fix a potential NULL-pointer exception in rxrpc_do_sendmsg().  The call
state check that I added should have gone into the else-body of the
if-statement where we actually have a call to check.

Found by CoverityScan CID#1414316 ("Dereference after null check").

Fixes: 540b1c48 ("rxrpc: Fix deadlock between call creation and sendmsg/recvmsg")
Reported-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

sched/headers: Prepare to move signal wakeup & sigpending methods from <linux/sched.h> into <linux/sched/signal.h>

Fix up affected files that include this signal functionality via sched.h.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

All the routines by which rxrpc is accessed from the outside are serialised
by means of the socket lock (sendmsg, recvmsg, bind,
rxrpc_kernel_begin_call(), ...) and this presents a problem:

 (1) If a number of calls on the same socket are in the process of
     connection to the same peer, a maximum of four concurrent live calls
     are permitted before further calls need to wait for a slot.

 (2) If a call is waiting for a slot, it is deep inside sendmsg() or
     rxrpc_kernel_begin_call() and the entry function is holding the socket
     lock.

 (3) sendmsg() and recvmsg() or the in-kernel equivalents are prevented
     from servicing the other calls as they need to take the socket lock to
     do so.

 (4) The socket is stuck until a call is aborted and makes its slot
     available to the waiter.

Fix this by:

 (1) Provide each call with a mutex ('user_mutex') that arbitrates access
     by the users of rxrpc separately for each specific call.

 (2) Make rxrpc_sendmsg() and rxrpc_recvmsg() unlock the socket as soon as
     they've got a call and taken its mutex.

     Note that I'm returning EWOULDBLOCK from recvmsg() if MSG_DONTWAIT is
     set but someone else has the lock.  Should I instead only return
     EWOULDBLOCK if there's nothing currently to be done on a socket, and
     sleep in this particular instance because there is something to be
     done, but we appear to be blocked by the interrupt handler doing its
     ping?

 (3) Make rxrpc_new_client_call() unlock the socket after allocating a new
     call, locking its user mutex and adding it to the socket's call tree.
     The call is returned locked so that sendmsg() can add data to it
     immediately.

     From the moment the call is in the socket tree, it is subject to
     access by sendmsg() and recvmsg() - even if it isn't connected yet.

 (4) Lock new service calls in the UDP data_ready handler (in
     rxrpc_new_incoming_call()) because they may already be in the socket's
     tree and the data_ready handler makes them live immediately if a user
     ID has already been preassigned.

     Note that the new call is locked before any notifications are sent
     that it is live, so doing mutex_trylock() *ought* to always succeed.
     Userspace is prevented from doing sendmsg() on calls that are in a
     too-early state in rxrpc_do_sendmsg().

 (5) Make rxrpc_new_incoming_call() return the call with the user mutex
     held so that a ping can be scheduled immediately under it.

     Note that it might be worth moving the ping call into
     rxrpc_new_incoming_call() and then we can drop the mutex there.

 (6) Make rxrpc_accept_call() take the lock on the call it is accepting and
     release the socket after adding the call to the socket's tree.  This
     is slightly tricky as we've dequeued the call by that point and have
     to requeue it.

     Note that requeuing emits a trace event.

 (7) Make rxrpc_kernel_send_data() and rxrpc_kernel_recv_data() take the
     new mutex immediately and don't bother with the socket mutex at all.

This patch has the nice bonus that calls on the same socket are now to some
extent parallelisable.

Note that we might want to move rxrpc_service_prealloc() calls out from the
socket lock and give it its own lock, so that we don't hang progress in
other calls because we're waiting for the allocator.

We probably also want to avoid calling rxrpc_notify_socket() from within
the socket lock (rxrpc_accept_call()).
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Tested-by: NMarc Dionne <marc.c.dionne@auristor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>