In the syslog applet, when a message was not fully received, we must request
for more data by calling appctx_need_more_data() and not by setting
CF_READ_DONTWAIT flag on the request channel. Indeed, this flag is only used
to only try a read at once.
This patch could be backported as far as 2.4. On 2.5 and 2.4,
applet_need_more_data() must be replaced by si_cant_get().
Replace all BUG_ON() on frame allocation failure by a CONNECTION_CLOSE
sending with INTERNAL_ERROR code. This can happen for the following
cases :
* sending of MAX_STREAM_DATA
* sending of MAX_DATA
* sending of MAX_STREAMS_BIDI
In other cases (STREAM, STOP_SENDING, RESET_STREAM), an allocation
failure will only result in the current operation to be interrupted and
retried later. However, it may be desirable in the future to replace
this with a simpler CONNECTION_CLOSE emission to recover better under a
memory pressure issue.
This should be backported up to 2.7.
Emit a CONNECTION_CLOSE with INTERNAL_ERROR code each time qcs
allocation fails. This can happen in two cases :
* when creating a local stream through application layer
* when instantiating a remote stream through qcc_get_qcs()
In both cases, error paths are already in place to interrupt the current
operation and a CONNECTION_CLOSE will be emitted soon after.
This should be backported up to 2.7.
Add BUG_ON() statements to ensure qcc_emit_cc()/qcc_emit_cc_app() is not
called more than one time for each connection. This should improve code
resilience of MUX-QUIC and H3 and it will ensure that a scheduled
CONNECTION_CLOSE is not overwritten by another one with a different
error code.
This commit relies on the previous one to ensure all QUIC operations are
not conducted as soon as a CONNECTION_CLOSE has been prepared :
commit d7fbf458f8a4c5b09cbf0da0208fbad70caaca33
MINOR: mux-quic: interrupt most operations if CONNECTION_CLOSE scheduled
This should be backported up to 2.7.
Ensure that external MUX operations are interrupted if a
CONNECTION_CLOSE is scheduled. This was already the cases for some
functions. This is extended to the qcc_recv*() family for
MAX_STREAM_DATA, RESET_STREAM and STOP_SENDING.
Also, qcc_release_remote_stream() is skipped in qcs_destroy() if a
CONNECTION_CLOSE is already scheduled.
All of this will ensure we only proceed to minimal treatment as soon as
a CONNECTION_CLOSE is prepared. Indeed, all sending and receiving is
stopped as soon as a CONNECTION_CLOSE is emitted so only internal
cleanup code should be necessary at this stage.
This should prevent a registered CONNECTION_CLOSE error status to be
overwritten by an error in a follow-up treatment.
This should be backported up to 2.7.
HTTP/3 graceful shutdown operation is used to emit a GOAWAY followed by
a CONNECTION_CLOSE with H3_NO_ERROR status. It is used for every
connection on release which means that if a CONNECTION_CLOSE was already
registered for a previous error, its status code is overwritten.
To fix this, skip shutdown operation if a CONNECTION_CLOSE is already
registered at the MUX level. This ensures that the correct error status
is reported to the peer.
This should be backported up to 2.6. Note that qc_shutdown() does not
exists on 2.6 so modification will have to be made directly in
qc_release() as followed :
diff --git a/src/mux_quic.c b/src/mux_quic.c
index 49df0dc418..3463222956 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -1766,19 +1766,21 @@ static void qc_release(struct qcc *qcc)
TRACE_ENTER(QMUX_EV_QCC_END, conn);
- if (qcc->app_ops && qcc->app_ops->shutdown) {
- /* Application protocol with dedicated connection closing
- * procedure.
- */
- qcc->app_ops->shutdown(qcc->ctx);
+ if (!(qcc->flags & QC_CF_CC_EMIT)) {
+ if (qcc->app_ops && qcc->app_ops->shutdown) {
+ /* Application protocol with dedicated connection closing
+ * procedure.
+ */
+ qcc->app_ops->shutdown(qcc->ctx);
- /* useful if application protocol should emit some closing
- * frames. For example HTTP/3 GOAWAY frame.
- */
- qc_send(qcc);
- }
- else {
- qcc_emit_cc_app(qcc, QC_ERR_NO_ERROR, 0);
+ /* useful if application protocol should emit some closing
+ * frames. For example HTTP/3 GOAWAY frame.
+ */
+ qc_send(qcc);
+ }
+ else {
+ qcc_emit_cc_app(qcc, QC_ERR_NO_ERROR, 0);
+ }
}
if (qcc->task) {
A H3 unidirectional stream is always opened with its stream type first
encoded as a QUIC variable integer. If the STREAM frame contains some
data but not enough to decode this varint, haproxy would crash due to an
ABORT_NOW() statement.
To fix this, ensure we support an incomplete stream type. In this case,
h3_init_uni_stream() returns 0 and the buffer content is not cleared.
Stream decoding will resume when new data are received for this stream
which should be enough to decode the stream type varint.
This bug has never occured on production because standard H3 stream types
are small enough to be encoded on a single byte.
This should be backported up to 2.6.
Instead of reporting the inaccurate "malloc_trim() support" on -vv, let's
report the case where the memory allocator was actively replaced from the
one used at build time, as this is the corner case we want to be cautious
about. We also put a tainted bit when this happens so that it's possible
to detect it at run time (e.g. the user might have inherited it from an
environment variable during a reload operation).
The now unused is_trim_enabled() function was finally dropped.
The runtime detection of the default memory allocator was broken by
Commit d8a97d8f6 ("BUG/MINOR: illegal use of the malloc_trim() function
if jemalloc is used") due to a misunderstanding of its role. The purpose
is not to detect whether we're on non-jemalloc but whether or not the
allocator was changed from the one we booted with, in which case we must
be extra cautious and absolutely refrain from calling malloc_trim() and
its friends.
This was done only to drop the message saying that malloc_trim() is
supported, which will be totally removed in another commit, and could
possibly be removed even in older versions if this patch would get
backported since in the end it provides limited value.
There's a recurring issue regarding shared library loading from Lua. If
the imported library is linked with a different version of openssl but
doesn't use it, the check will trigger and emit a warning. In practise
it's not necessarily a problem as long as the API is the same, because
all symbols are replaced and the library will use the included ssl lib.
It's only a problem if the library comes with a different API because
the dynamic linker will only replace known symbols with ours, and not
all. Thus the loaded lib may call (via a static inline or a macro) a
few different symbols that will allocate or preinitialize structures,
and which will then pass them to the common symbols coming from a
different and incompatible lib, exactly what happens to users of Lua's
luaossl when building haproxy with quictls and without rebuilding
luaossl.
In order to better address this situation, we now define groups of
symbols that must always appear/disappear in a consistent way. It's OK
if they're all absent from either haproxy or the lib, it means that one
of them doesn't use them so there's no problem. But if any of them is
defined on any side, all of them must be in the exact same state on the
two sides. The symbols are represented using a bit in a mask, and the
mask of the group of other symbols they're related to. This allows to
check 64 symbols, this should be OK for a while. The first ones that
are tested for now are symbols whose combination differs between
openssl versions 1.0, 1.1, and 3.0 as well as quictls. Thus a difference
there will indicate upcoming trouble, but no error will mean that we're
running on a seemingly compatible API and that all symbols should be
replaced at once.
The same mechanism could possibly be used for pcre/pcre2, zlib and the
few other optional libs that may occasionally cause runtime issues when
used by dependencies, provided that discriminatory symbols are found to
distinguish them. But in practice such issues are pretty rare, mainly
because loading standard libs via Lua on a custom build of haproxy is
not pretty common.
In the event that further symbol compatibility issues would be reported
in the future, backporting this patch as well as the following series
might be an acceptable solution given that the scope of changes is very
narrow (the malloc stuff is needed so that the malloc/free tests can be
dropped):
BUG/MINOR: illegal use of the malloc_trim() function if jemalloc is used
MINOR: pools: make sure 'no-memory-trimming' is always used
MINOR: pools: intercept malloc_trim() instead of trying to plug holes
MEDIUM: pools: move the compat code from trim_all_pools() to malloc_trim()
MINOR: pools: export trim_all_pools()
MINOR: pattern: use trim_all_pools() instead of a conditional malloc_trim()
MINOR: tools: relax dlopen() on malloc/free checks
Now that we can provide a safe malloc_trim() we don't need to detect
anymore that some dependencies use a different set of malloc/free
functions than ours because they will use the same as those we're
seeing, and we control their use of malloc_trim(). The comment about
the incompatibility with DEBUG_MEM_STATS is not true anymore either
since the feature relies on macros so we're now OK.
This will stop catching libraries linked against glibc's allocator
when haproxy is natively built with jemalloc. This was especially
annoying since dlopen() on a lib depending on jemalloc() tends to
fail on TLS issues.
We already have some generic code in trim_all_pools() to implement the
equivalent of malloc_trim() on jemalloc and macos. Instead of keeping the
logic there, let's just move it to our own malloc_trim() implementation
so that we can unify the mechanism and the logic. Now any low-level code
calling malloc_trim() will either be disabled by haproxy's config if the
user decides to, or will be mapped to the equivalent mechanism if malloc()
was intercepted by a preloaded jemalloc.
Trim_all_pools() preserves the benefit of serializing threads (which we
must not impose to other libs which could come with their own threads).
It means that our own code should mostly use trim_all_pools() instead of
calling malloc_trim() directly.
As reported by Miroslav in commit d8a97d8f6 ("BUG/MINOR: illegal use of
the malloc_trim() function if jemalloc is used") there are still occasional
cases where it's discovered that malloc_trim() is being used without its
suitability being checked first. This is a problem when using another
incompatible allocator. But there's a class of use cases we'll never be
able to cover, it's dynamic libraries loaded from Lua. In order to address
this more reliably, we now define our own malloc_trim() that calls the
previous one after checking that the feature is supported and that the
allocator is the expected one. This way child libraries that would call
it will also be safe.
The function is intentionally left defined all the time so that it will
be possible to clean up some code that uses it by removing ifdefs.
The global option 'no-memory-trimming' was added in 2.6 with commit
c4e56dc58 ("MINOR: pools: add a new global option "no-memory-trimming"")
but there were some cases left where it was not considered. Let's make
is_trim_enabled() also consider it.
Complete traces with information from qcc and qcs instances about
flow-control level. This should help to debug further issue on sending.
This must be backported up to 2.7.
Change the trace from developer to data level whenever the flow control
limitation is updated following a MAX_DATA or MAX_STREAM_DATA reception.
This should be backported up to 2.7.
Add traces for _qc_send_qcs() function. Most notably, traces have been
added each time a qc_stream_desc buffer allocation fails and when stream
or connection flow-level is reached. This should improve debugging for
emission issues.
This must be backported up to 2.7.
Connection flow-control level calculation is a bit complicated. To
ensure it is never exceeded, each time a transfer occurs from a
qcs.tx.buf to its qc_stream_desc buffer it is accounted in
qcc.tx.offsets at the connection level. This value is not decremented
even if the corresponding STREAM frame is rejected by the quic-conn
layer as its emission will be retried later.
In normal cases this works as expected. However there is an issue if a
qcs instance is removed with prepared data left. In this case, its data
is still accounted in qcc.tx.offsets despite being removed which may
block other streams. This happens every time a qcs is reset with
remaining data which will be discarded in favor of a RESET_STREAM frame.
To fix this, if a stream has prepared data in qcc_reset_stream(), it is
decremented from qcc.tx.offsets. A BUG_ON() has been added to ensure
qcs_destroy() is never called for a stream with prepared data left.
This bug can cause two issues :
* transfer freeze as data unsent from closed streams still count on the
connection flow-control limit and will block other streams. Note that
this issue was not reproduced so it's unsure if this really happens
without the following issue first.
* a crash on a BUG_ON() statement in qc_send() loop over
qc_send_frames(). Streams may remained in the send list with nothing
to send due to connection flow-control limit. However, limit is never
reached through qcc_streams_sent_done() so QC_CF_BLK_MFCTL flag is not
set which will allow the loop to continue.
The last case was reproduced after several minutes of testing using the
following command :
$ ngtcp2-client --exit-on-all-streams-close -t 0.1 -r 0.1 \
--max-data=100K -n32 \
127.0.0.1 20443 "https://127.0.0.1:20443/?s=1g" 2>/dev/null
This should fix github issues #2049 and #2074.
In the event that HAProxy is linked with the jemalloc library, it is still
shown that malloc_trim() is enabled when executing "haproxy -vv":
..
Support for malloc_trim() is enabled.
..
It's not so much a problem as it is that malloc_trim() is called in the
pat_ref_purge_range() function without any checking.
This was solved by setting the using_default_allocator variable to the
correct value in the detect_allocator() function and before calling
malloc_trim() it is checked whether the function should be called.
Starting haproxy with -dL helps enumerate the list of libraries in use.
But sometimes in order to go further we'd like to see their address
ranges. This is already supported on the CLI's "show libs" but not on
the command line where it can sometimes help troubleshoot startup issues.
Let's dump them when in verbose mode. This way it doesn't change the
existing behavior for those trying to enumerate libs to produce an archive.
When threads are disabled, the compiler complains that we might be
accessing tg->abs[] out of bounds since the array is of size 1. It
cannot know that the condition to do this is never met, and given
that it's not in a fast path, we can make it more obvious.
Building without thread support was broken in 2.8-dev2 with commit
7e70bfc8c ("MINOR: threads: add a thread_harmless_end() version that
doesn't wait") that forgot to define the function for the threadless
cases. No backport is needed.
qc_notify_send() is used to wake up the MUX layer for sending. This
function first ensures that all sending condition are met to avoid to
wake up the MUX for unnecessarily.
One of this condition is to check if there is room in the congestion
window. However, when probe packets must be sent due to a PTO
expiration, RFC 9002 explicitely mentions that the congestion window
must be ignored which was not the case prior to this patch.
This commit fixes this by first setting <pto_probe> of 01RTT packet
space before invoking qc_notify_send(). This ensures that congestion
window won't be checked anymore to wake up the MUX layer until probing
packets are sent.
This commit replaces the following one which was not sufficient :
commit e25fce03eb
BUG/MINOR: quic: Dysfunctional 01RTT packet number space probing
This should be backported up to 2.7.
On PTO probe timeout expiration, a probe packet must be emitted.
quic_pto_pktns() is used to determine for which packet space the timer
has expired. However, if MUX is already subscribed for sending, it is
woken up without checking first if this happened for the 01RTT packet
space.
It is unsure that this is really a bug as in most cases, MUX is
established only after Initial and Handshake packet spaces are removed.
However, the situation is not se clear when 0-RTT is used. For this
reason, adjust the code to explicitely check for the 01RTT packet space
before waking up the MUX layer.
This should be backported up to 2.6. Note that qc_notify_send() does not
exists in 2.6 so it should be replaced by the explicit block checking
(qc->subs && qc->subs->events & SUB_RETRY_SEND).
If appctx_new_on() fails to allocate a task, it will not remove the
freshly allocated sedesc from the appctx despite freeing it, causing
a UAF. Let's only assign appctx->sedesc upon success.
This needs to be backported to 2.6. In 2.6 the function is slightly
different and called appctx_new(), though the issue is exactly the
same.
In h1c_frt_stream_new() and h1c_bck_stream_new(), if we fail to completely
initialize the freshly allocated h1s, typically because sc_attach_mux()
fails, we must use h1s_destroy() to de-initialize it. Otherwise it stays
attached to the h1c when released, causing use-after-free upon the next
wakeup. This can be triggered upon memory shortage.
This needs to be backported to 2.6.
Using -dMfail alone does nothing unless tune.fail-alloc is set, which
renders it pretty useless as-is, and is not intuitive. Let's change
this so that the filure rate is preset to 1% when the option is set on
the command line. This allows to inject failures without having to edit
the configuration.
b_alloc() is used to allocate a buffer. We can provoke fault injection
based on forced memory allocation failures using -dMfail on the command
line, but we know that the buffer_wait list is a bit weak and doesn't
always recover well. As such, submitting buffer allocation to such a
treatment seriously limits the usefulness of -dMfail which cannot really
be used for other purposes. Let's just disable it for buffers for now.
If we fail to allocate a new stream in sc_new_from_endp(), and the call
to sc_new() allocated the sedesc itself (which normally doesn't happen),
then it doesn't get released on the failure path. Let's explicitly
handle this case so that it's not overlooked and avoids some head
scratching sessions.
This may be backported to 2.6.
There's an occasional crash that can be triggered in sc_detach_endp()
when calling conn->mux->detach() upon memory allocation error. The
problem in fact comes from sc_attach_mux(), which doesn't reset the
sc type flags upon tasklet allocation failure, leading to an attempt
at detaching an incompletely initialized stconn. Let's just attach
the sc after the tasklet allocation succeeds, not before.
This must be backported to 2.6.
On the allocation error path in h2_init() we may check if
h2c->wait_event.tasklet needs to be released but it has not yet been
zeroed. Let's do this before jumping to the freeing location.
This needs to be backported to all maintained versions.
In h2s_close() we may dereference h2s->sd to get the sc, but this
function may be called on allocation error paths, so we must check
for this specific condition. Let's also update the comment to make
it explicitly permitted.
This needs to be backported to 2.6.
In stream_free() if we fail to allocate s->scb() we go to the path where
we try to free it, and it doesn't like being called with a null at all.
It's easily reproducible with -dMfail,no-cache and "tune.fail-alloc 10"
in the global section.
This must be backported to 2.6.
This bug arrived with this commit:
"MINOR: quic: implement qc_notify_send()".
The ->tx.pto_probe variable was no more set when qc_processt_timer() the timer
task for the connection responsible of detecting packet loss and probing upon
PTO expiration leading to interrupted stream transfers. This was revealed by
blackhole interop failed tests where one could see that qc_process_timer()
was wakeup without traces as follows in the log file:
"needs to probe 01RTT packet number space"
Must be backported to 2.7 and to 2.6 if the commit mentionned above
is backported to 2.6 in the meantime.
The ACK frame range of packets were handled from the largest to the smallest
packet number, leading to big number of ebtree insertions when the packet are
handled in the inverse way they are sent. This was detected a long time ago
but left in the code to stress our implementation. It is time to be more
efficient and process the packet so that to avoid useless ebtree insertions.
Modify qc_ackrng_pkts() responsible of handling the acknowledged packets from an
ACK frame range of acknowledged packets.
Must be backported to 2.7.
Despite having replaced the SSL BIOs to use our own raw_sock layer, we
still didn't exploit the CO_SFL_MSG_MORE flag which is pretty useful to
avoid sending incomplete packets. It's particularly important for SSL
since the extra overhead almost guarantees that each send() will be
followed by an incomplete (and often odd-sided) segment.
We already have an xprt_st set of flags to pass info to the various
layers, so let's just add a new one, SSL_SOCK_SEND_MORE, that is set
or cleared during ssl_sock_from_buf() to transfer the knowledge of
CO_SFL_MSG_MORE. This way we can recover this information and pass
it to raw_sock.
This alone is sufficient to increase by ~5-10% the H2 bandwidth over
SSL when multiple streams are used in parallel.
Traces show that sendto() rarely has MSG_MORE on H2 despite sending
multiple buffers. The reason is that the loop iterating over the buffer
ring doesn't have this info and doesn't pass it down.
But now we know how many buffers are left to be sent, so we know whether
or not the current buffer is the last one. As such we can set this flag
for all buffers but the last one.
Before muxes were used, we used to refrain from reading past the
buffer's reserve. But with muxes which have their own buffer, this
rule was a bit forgotten, resulting in an extraneous read to be
performed just because the rx buffer cannot be entirely transferred
to the stream layer:
sendto(12, "GET /?s=16k HTTP/1.1\r\nhost: 127."..., 84, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 84
recvfrom(12, "HTTP/1.1 200\r\nContent-length: 16"..., 16320, 0, NULL, NULL) = 16320
recvfrom(12, ".123456789.12345", 16, 0, NULL, NULL) = 16
recvfrom(12, "6789.123456789.12345678\n.1234567"..., 15244, 0, NULL, NULL) = 182
recvfrom(12, 0x1e5d5d6, 15062, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
Here the server sends 16kB of payload after a headers block, the mux reads
16320 into the ibuf, and the stream layer consumes 15360 from the first
h1_rcv_buf(), which leaves 960 into the buffer and releases a few indexes.
The buffer cannot be realigned due to these remaining data, and a subsequent
read is made on 16 bytes, then again on 182 bytes.
By avoiding to read too much on the first call, we can avoid needlessly
filling this buffer:
recvfrom(12, "HTTP/1.1 200\r\nContent-length: 16"..., 15360, 0, NULL, NULL) = 15360
recvfrom(12, "456789.123456789.123456789.12345"..., 16220, 0, NULL, NULL) = 1158
recvfrom(12, 0x1d52a3a, 15062, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
This is much more efficient and uses less RAM since the first buffer that
was emptied can now be released.
Note that a further improvement (tested) consists in reading even less
(typically 1kB) so that most of the data are transferred in zero-copy, and
are not read until process_stream() is scheduled. This patch doesn't do that
for now so that it can be backported without any obscure impact.
CertiK Skyfall Team reported that passing an index greater than
QPACK_SHT_SIZE in a qpack instruction referencing a literal field
name with name reference or and indexed field line will cause a
read out of bounds that may crash the process, and confirmed that
this fix addresses the issue.
This needs to be backported as far as 2.5.
When sc-add-gpc() action was implemented in 5a72d03 ("MINOR:
stick-table: implement the sc-add-gpc() action"), its usage was
only documented for "http-request", but according to the code it
now applies everywhere sc-inc-gpc() is mentioned.
Adding the missing entries in the doc everywhere the action may
be used.
The issue was detected by the haproxy-controller bot and was reported
by Pratik Mohanty and Marko Juraga.
No backport needed, unless 5a72d03 ("MINOR: stick-table: implement the
sc-add-gpc() action") is being backported.
sc-add-gpc() was implemented in 5a72d03 ("MINOR: stick-table:
implement the sc-add-gpc() action")
This new action was exposed everywhere sc-inc-gpc() is available,
except for http-after-response.
But there doesn't seem to be a technical constraint that prevents us from
exposing it in http-after-response.
It was probably overlooked, let's add it.
No backport needed, unless 5a72d03 ("MINOR: stick-table: implement the
sc-add-gpc() action") is being backported.
This patch follows this one which was not sufficient:
"BUG/MINOR: quic: Missing STREAM frame length updates"
Indeed, it is not sufficient to update the ->len and ->offset member
of a STREAM frame to move it forward. The data pointer must also be updated.
This is not done by the STREAM frame builder.
Must be backported to 2.6 and 2.7.
Emeric noticed that h2 bit-rate performance was always slightly lower
than h1 when the CPU is saturated. Strace showed that we were always
data in 2kB chunks, corresponding to the max_record size. What's
happening is that when this mechanism of dynamic record size was
introduced, the STREAMER flag at the stream level was relied upon.
Since all this was moved to the muxes, the flag has to be passed as
an argument to the snd_buf() function, but the mux h2 did not use it
despite a comment mentioning it, probably because before the multi-buf
it was not easy to figure the status of the buffer.
The solution here consists in checking if the mbuf is congested or not,
by checking if it has more than one buffer allocated. If so we set the
CO_SFL_STREAMER flag, otherwise we don't. This way moderate size
exchanges continue to be made over small chunks, but downloads will
be able to use the large ones.
While it could be backported to all supported versions, it would be
better to limit it to the last LTS, so let's do it for 2.7 and 2.6 only.
This patch requires previous commit "MINOR: buffer: add br_single() to
check if a buffer ring has more than one buf".
During performance tests, Emeric faced a case where the wakeups of
sc_conn_io_cb() caused by h2_resume_each_sending_h2s() was multiplied
by 5-50 and a lot of CPU was being spent doing this for apparently no
reason.
The culprit is h2_send() not behaving well with congested buffers and
small SSL records. What happens when the output is congested is that
all buffers are full, and data are emitted in 2kB chunks, which are
sufficient to wake all streams up again to ask them to send data again,
something that will obviously only work for one of them at best, and
waste a lot of CPU in wakeups and memcpy() due to the small buffers.
When this happens, the performance can be divided by 2-2.5 on large
objects.
Here the chosen solution against this is to keep in mind that as long
as there are still at least two buffers in the ring after calling
xprt->snd_buf(), it means that the output is congested and there's
no point trying again, because these data will just be placed into
such buffers and will wait there. Instead we only mark the buffer
decongested once we're back to a single allocated buffer in the ring.
By doing so we preserve the ability to deal with large concurrent
bursts while not causing a thundering herd by waking all streams for
almost nothing.
This needs to be backported to 2.7 and 2.6. Other versions could
benefit from it as well but it's not strictly necessary, and we can
reconsider this option if some excess calls to sc_conn_io_cb() are
faced.
Note that this fix depends on this recent commit:
MINOR: buffer: add br_single() to check if a buffer ring has more than one buf
It's cheaper and cleaner than using br_count()==1 given that it just compares
two indexes, and that a ring having a single buffer is in a special case where
it is between empty and used up-to-1. In other words it's not congested.
When detaching a stream, if it's the last one and the mbuf is blocked,
we leave without freeing the stream yet. We also refresh the h2c task's
timeout, except that it's possible that there's no such task in case
there is no client timeout, causing a crash. The fix just consists in
doing this when the task exists.
This bug has always been there and is extremely hard to meet even
without a client timeout. This fix has to be backported to all
branches, but it's unlikely anyone has ever met it anyay.
