If the stream closes and quits while there's no room in the mux buffer
to send an RST frame, next time it is attempted it will not lead to
the connection being closed because the conn_stream will have been
released and the KILL_CONN flag with it as well.
This patch reserves a new H2_SF_KILL_CONN flag that is copied from
the CS when calling shut{r,w} so that the stream remains autonomous
on this even when the conn_stream leaves.
This should ideally be backported to 1.9 though it depends on several
previous patches that may or may not be suitable for backporting. The
severity is very low so there's no need to insist in case of trouble.
In h2s_wake_one_stream() we used to rely on the temporary flags used to
adjust the CS to determine the new h2s state. This really is not convenient
and creates far too many dependencies. This commit just moves the same
condition to the places where the temporary flags were set so that we
don't have to rely on these anymore. Whether these are relevant or not
was not the subject of the operation, what matters was to make sure the
conditions to adjust the stream's state and the CS's flags remain the
same. Later it could be studied if these conditions are correct or not.
h2s_wake_one_stream() has access to all the required elements to update
the connstream's flags and figure the necessary state transitions, so
let's move the conditions there from h2_wake_some_streams().
It's problematic to have to pass some CS flags to this function because
that forces some h2s state transistions to update them just in time
while some of them are supposed to only be updated during I/O operations.
As a first step this patch transfers the decision to pass CS_FL_ERR_PENDING
from the caller to the leaf function h2s_wake_one_stream(). It is easy
since this is the only flag passed there and it depends on the position of
the stream relative to the last_sid if it was set.
h2_wake_some_streams() first looks up streams whose IDs are greater than
or equal to last+1, then checks if the id is lower than or equal to last,
which by definition will never match. Let's remove this confusing leftover
from ancient code.
These functions may fail to emit an RST or an empty DATA frame because
the mux is full or busy. Then they subscribe the h2s and try again.
However when doing so, they will already have marked the error state on
the stream and will not pass anymore through the sequence resulting in
the failed frame to be attempted to be sent again nor to the close to
be done, instead they will return a success.
It is important to only leave when the stream is already closed, but
to go through the whole sequence otherwise.
This patch should ideally be backported to 1.9 though it's possible that
the lack of the WANT_SHUT* flags makes this difficult or dangerous. The
severity is low enough to avoid this in case of trouble.
It was only set and not consumed after the previous change. The reason
is that the task's context always contains the relevant information,
so there is no need for a second pointer.
This one used to rely on the combined return statuses of the shutr/w
functions but now that we have the H2_SF_WANT_SHUT{R,W} flags we don't
need this anymore if we properly remove these flags after their operations
succeed. This is what this patch does.
Currently when a shutr/shutw fails due to lack of buffer space, we abuse
the wait_event's handle pointer to place up to two bits there in addition
to the original pointer. This pointer is not used for anything but this
and overall the intent becomes clearer with h2s flags than with these
two alien bits in the pointer, so let's use clean flags now.
Lots of places were using LIST_ISEMPTY() to detect if a stream belongs
to one of the send lists or to detect if a connection was already
waiting for a buffer or attached to an idle list. Since these ones are
not list heads but list elements, let's use LIST_ADDED() instead.
In this long thread, Maciej Zdeb reported that the H2 mux was still
going through endless loops from time to time :
https://www.mail-archive.com/haproxy@formilux.org/msg33709.html
What happens is the following :
- in h2s_frt_make_resp_data() we can set H2_SF_BLK_SFCTL and remove the
stream from the send_list
- then in h2_shutr() and h2_shutw(), we check if the list is empty before
subscribing the element, which is true after the case above
- then in h2c_update_all_ws() we still have H2_SF_BLK_SFCTL with the item
in the send_list, thus LIST_ADDQ() adds it a second time.
This patch adds a check of list emptiness before performing the LIST_ADDQ()
when the flow control window opens. Maciej reported that it reliably fixed
the problem for him.
As later discussed with Olivier, this fixes the consequence of the issue
rather than its cause. The root cause is that a stream should never be in
the send_list with a blocking flag set and the various places that can lead
to this situation must be revisited. Thus another fix is expected soon for
this issue, which will require some observation. In the mean time this one
is easy enough to validate and to backport.
Many thanks to Maciej for testing several versions of the patch, each
time providing detailed traces which allowed to nail the problem down.
This patch must be backported to 1.9.
When we have to stop sending due to the stream flow control, don't check
if send_wait is NULL to know if we're in the send_list, because at this
point it'll always be NULL, while we're probably in the list.
Use LIST_ISEMPTY(&h2s->list) instead.
Failing to do so mean we might be added in the send_list when flow control
allows us to emit again, while we're already in it.
While I'm here, replace LIST_DEL + LIST_INIT by LIST_DEL_INIT.
This should be backported to 1.9.
In h2_detach(), if we still have a send_wait pointer, because we woke the
tasklet up, but it hasn't ran yet, explicitely set send_wait to NULL after
we removed the tasklet from the task list.
Failure to do so may lead to crashes if the h2s isn't immediately destroyed,
because we considered there were still something to send.
This should be backported to 1.9.
A typo was introduced in the following commit : 927b88ba0 ("BUG/MAJOR:
mux-h2: fix race condition between close on both ends") making the test
on h2s->cs never being done and h2c->cs being dereferenced without being
tested. This also confirms that this condition does not happen on this
side but better fix it right now to be safe.
This must be backported to 1.9.
Since previous commit it's not needed anymore to test a task pointer
before calling task_destory() so let's just remove these tests from
the various callers before they become confusing. The function's
arguments were also documented. The same should probably be done
with tasklet_free() which involves a test in roughly half of the
call places.
If when receiving an H2 response we fail to add an EOM block after too
large a trailers block, we must not leave the trailers block alone as it
violates the internal assumptions by not being followed by an EOM, even
when an error is reported. We must then make sure the error will safely
be reported to upper layers and that no attempt will be made to forward
partial blocks.
This must be backported to 1.9.
In message https://www.mail-archive.com/haproxy@formilux.org/msg33541.html
Patrick Hemmer reported an interesting bug affecting H2 and trailers.
The problem is that in order to close the stream we have to see the EOM
block, but nothing guarantees it will atomically be delivered with the
trailers block(s). So the code currently waits for it by returning zero
when it was not found, resulting in the caller (h2_snd_buf()) to loop
forever calling it again.
The current internal connection/connstream API doesn't allow a send
actor to notify its caller that it cannot process the data until it
gets more, so even returning zero will only lead to calls in loops
without any guarantee that any progress will be made.
Some late amendments to HTX already guaranteed the atomicity of the
trailers block during snd_buf(), which is currently ensured by the
fact that producers create exactly one such trailers block for all
trailers. So in practice we can only loop between trailers and EOM.
This patch changes the behaviour by making h2s_htx_make_trailers()
become atomic by not consuming the EOM block. This way either it finds
the end of trailers marker (empty line) or it fails. Once it sends the
trailers block, ES is set so the stream turns HLOC or CLOSED. Thanks
to previous patch "MEDIUM: mux-h2: discard contents that are to be sent
after a shutdown" is is now safe to interrupt outgoing data processing,
and the late EOM block will silently be discarded when the caller
finally sends it.
This is a bit tricky but should remain solid by design, and seems like
the only option we have that is compatible with 1.9, where it must be
backported along with the aforementioned patch.
In h2_snd_buf() we discard any possible buffer contents requested to be
sent after a close or an error. But in practice we can extend this to
any case where the stream is locally half-closed since it means we will
never be able to send these data anymore.
For now it must not change anything, but it will be used by subsequent
patches to discard lone a HTX EOM block arriving after the trailers
block.
In case a header frame carrying trailers just fits into the HTX buffer
but leaves no room for the EOM block, we used to return the same code
as the one indicating we're missing data. This could would result in
such frames causing timeouts instead of immediate clean aborts. Now
they are properly reported as stream errors (since the frame was
decoded and the compression context is still synchronized).
This must be backported to 1.9.
When sending trailers, we may face an empty HTX trailers block or even
have to discard some of the headers there and be left with nothing to
send. RFC7540 forbids sending of empty HEADERS frames, so in this case
we turn to DATA frames (which is possible since after other DATA).
The code used to only check the input frame's contents to decide whether
or not to switch to a DATA frame, it didn't consider the possibility that
the frame only used to contain headers discarded later, thus it could still
emit an empty HEADERS frame in such a case. This patch makes sure that the
output frame size is checked instead to take the decision.
This patch must be backported to 1.9. In practice this situation is never
encountered since the discarded headers have really nothing to do in a
trailers block.
In h2c_decode_headers(), now that we support CONTINUATION frames, we
try to defragment all pending frames at once before processing them.
However if the first is exactly full and the second cannot be parsed,
we don't detect the problem and we wait for the next part forever due
to an incorrect check on exit; we must abort the processing as soon as
the current frame remains full after defragmentation as in this case
there is no way to make forward progress.
Thanks to Yves Lafon for providing traces exhibiting the problem.
This must be backported to 1.9.
For most of the xprt methods, provide a xprt_ctx. This will be useful later
when we'll want to be able to stack xprts.
The init() method now has to create and provide the said xprt_ctx if needed.
task_delete() was never used without calling task_free() just after, and
task_free() was only used on error pathes to destroy a just-created task,
so merge them into task_destroy(), that will remove the task from the
wait queue, and make sure the task is either destroyed immediately if it's
not in the run queue, or destroyed when it's supposed to run.
Instead of abusing the SUB_CALL_UNSUBSCRIBE flag, revamp the H2 code a bit
so that it just checks if h2s->sending_list is empty to know if the tasklet
of the stream_interface has been waken up or not.
send_wait is now set to NULL in h2_snd_buf() (ideally we'd set it to NULL
as soon as we're waking the tasklet, but it can't be done, because we still
need it in case we have to remove the tasklet from the task list).
In h2_subscribe(), don't add ourself to the send_list if we're already in it.
That may happen if we try to send and fail twice, as we're only removed
from the send_list if we managed to send data, to promote fairness.
Failing to do so can lead to either an infinite loop, or some random crashes,
as we'd get the same h2s in the send_list twice.
This should be backported to 1.9.
In the h1 and h2 muxes, make sure we unsubscribed before destroying the
mux context.
Failing to do so will lead in a segfault later, as the connection will
attempt to dereference its conn->send_wait or conn->recv_wait, which pointed
to the now-free'd mux context.
This was introduced by commit 39a96ee16eeec51774f9f52a783cf624a0de4ccb, so
should only be backported if that commit gets backported.
When a mux context is released, we must be sure it exists before dereferencing
it. The bug was introduced in the commit 39a96ee16 ("MEDIUM: muxes: Be prepared
to don't own connection during the release").
No need to backport this patch, expect if the commit 39a96ee16 is backported
too.
This happens during mux upgrades. In such case, when the destroy() callback is
called, the connection points to a different mux's context than the one passed
to the callback. It means the connection is owned by another mux. The old mux is
then released but the connection is not closed.
It is mandatory to handle mux upgrades, because during a mux upgrade, the
connection will be reassigned to another multiplexer. So when the old one is
destroyed, it does not own the connection anymore. Or in other words, conn->ctx
does not point to the old mux's context when its destroy() callback is
called. So we now rely on the multiplexer context do destroy it instead of the
connection.
In addition, h1_release() and h2_release() have also been updated in the same
way.
The mux's callback init() now take a pointer to a buffer as extra argument. It
must be used by the multiplexer as its input buffer. This buffer is always NULL
when a multiplexer is initialized with a fresh connection. But if a mux upgrade
is performed, it may be filled with existing data. Note that, for now, mux
upgrades are not supported. But this commit is mandatory to do so.
Instead of using the connection context to make the difference between a
frontend connection and a backend connection, we now rely on the function
conn_is_back().
A multiplexer must now set the flag MX_FL_HTX when it uses the HTX to structured
the data exchanged with channels. the muxes h1 and h2 set this flag. Of course,
for the mux h2, it is set on h2_htx_ops only.
Instead of using the same mux_ops structure for the legacy HTTP mode and the HTX
mode, a dedicated mux_ops is now used for the HTX mode. Same callbacks are used
for both. But the flags may be different depending on the mode used.
Modify h2c_restart_reading() to add a new parameter, to let it know if it
should consider if the buffer isn't empty when retrying to read or not, and
call h2c_restart_reading() using 0 as a parameter from h2_process_demux().
If we're leaving h2_process_demux() with a non-empty buffer, it means the
frame is incomplete, and we're waiting for more data, and if we already
subscribed, we'll be waken when more data are available.
Failing to do so means we'll be waken up in a loop until more data are
available.
This should be backported to 1.9.
Recent commit 63768a63d ("MEDIUM: mux-h2: Don't mix the end of the message
with the end of stream") introduced a race which may manifest itself with
small connection counts on large objects and large server timeouts in
legacy mode. Sometimes h2s_close() is called while the data layer is
subscribed to read events but nothing in the chain can cause this wake-up
to happen and some streams stall for a while at the end of a transfer
until the server timeout strikes and ends the stream completes.
We need to wake the stream up if it's subscribed to rx events there,
which is what this patch does. When the patch above is backported to
1.9, this patch will also have to be backported.
Previous commit 3ea351368 ("BUG/MEDIUM: h2: Remove the tasklet from the
task list if unsubscribing.") uncovered an issue which needs to be
addressed in the scheduler's API. The function task_remove_from_task_list()
was initially designed to remove a task from the running tasklet list from
within the scheduler, and had to be used in h2 to abort pending I/O events.
However this function was not designed to be idempotent, occasionally
causing a double removal from the tasklet list, with the second doing
nothing but affecting the apparent tasks count and making haproxy use
100% CPU on some tests consisting in stopping the client during some
transfers. The h2_unsubscribe() function can sometimes be called upon
stream exit after an error where the tasklet was possibly already
removed, so it.
This patch does 2 things :
- it renames task_remove_from_task_list() to
__task_remove_from_tasklet_list() to discourage users from calling
it. Also note the fix in the naming since it's a tasklet list and
not a task list. This function is still uesd from the scheduler.
- it adds a new, idempotent, task_remove_from_tasklet_list() function
which does nothing if the task is already not in the tasklet list.
This patch will need to be backported where the commit above is backported.
In h2_unsubscribe(), if we unsubscribe on SUB_CALL_UNSUBSCRIBE, then remove
ourself from the sending_list, and remove the tasklet from the task list.
We're probably about to destroy the stream anyway, so we don't want the
tasklet to run, or to stay in the sending_list, or it could lead to a crash.
This should be backpored to 1.9.
In h2_deferred_shut(), don't just set h2s->send_wait to NULL, instead, use
the same logic as in h2_snd_buf() and only do so if we successfully sent data
(or if we don't want to send them anymore). Setting it to NULL can lead to
crashes.
This should be backported to 1.9.
In h2s_notify_send(), use the new sending_list instead of using the old
way of setting hs->send_wait to NULL, failing to do so may lead to crashes.
This should be backported to 1.9.
In h2_deferred_shut(), only attempt to destroy the h2s if h2s->cs is NULL.
h2s->cs being non-NULL means it's still referenced by the stream interface,
so it may try to use it later, and that could lead to a crash.
This should be backported to 1.9.
The H2 multiplexer now sets CS_FL_EOI when it receives a frame with the ES
flag. And when the H2 streams is closed, it set the flag CS_FL_REOS.
This patch should be backported to 1.9.
On the send path, try to be fair, and make sure the first to attempt to
send data will actually be the first to send data when it's possible (ie
when the mux' buffer is not full anymore).
To do so, use a separate list element for the sending_list, and only remove
the h2s from the send_list/fctl_list if we successfully sent data. If we did
not, we'll keep our place in the list, and will be able to try again next time.
This should be backported to 1.9.
Some functions' roles and usage are far from being obvious, and diving
into this part each time requires deep concentration before starting to
understand who does what. Let's add a few comments which help figure
some of the useful pieces.
We tend to refrain from sending data a bit too much in the H2 mux :
whenever there are pending data in the buffer and we try to copy
something larger than 1/4 of the buffer we prefer to pause. This
is suboptimal for medium-sized objects which have to send their
headers and later their data.
This patch slightly changes this by allowing a copy of a large block
if it fits at once and if the realign cost is small, i.e. the pending
data are small or the block fits in the contiguous area. Depending on
the object size this measurably improves the download performance by
between 1 and 10%, and possibly lowers the transfer latency for medium
objects.
In h2_stop_senders(), when we're about to move the h2s about to send back
to the send_list, because we know the mux is full, instead of putting them
all in the send_list, put them back either in the fctl_list or the send_list
depending on if they are waiting for the flow control or not. This also makes
sure they're inserted in their arrival order and not reversed.
This should be backported to 1.9.
In h2_detach(), don't bother keeping the h2s even if it was waiting for
flow control if we no longer are subscribed for receiving or sending, as
nobody will do anything once we can write in the mux, anyway. Failing to do
so may lead to h2s being kept opened forever.
This should be backported to 1.9.
If we're waiting until we can send a shutr and/or a shutw, once we're done
and not considering sending anything, destroy the h2s, and eventually the
h2c if we're done with the whole connection, or it will never be done.
This should be backported to 1.9.
For conveniance, in HTTP muxes (h1 and h2), the end of the stream and the end of
the message are reported the same way to the stream, by setting the flag
CS_FL_EOS. In the stream-interface, when CS_FL_EOS is detected, a shutdown for
read is reported on the channel side. This is historical. With the legacy HTTP
layer, because the parsing is done by the stream in HTTP analyzers, the EOS
really means a shutdown for read.
Most of time, for muxes h1 and h2, it works pretty well, especially because the
keep-alive is handled by the muxes. The stream is only used for one
transaction. So mixing EOS and EOM is good enough. But not everytime. For now,
client aborts are only reported if it happens before the end of the request. It
is an error and it is properly handled. But because the EOS was already
reported, client aborts after the end of the request are silently
ignored. Eventually an error can be reported when the response is sent to the
client, if the sending fails. Otherwise, if the server does not reply fast
enough, an error is reported when the server timeout is reached. It is the
expected behaviour, excpect when the option abortonclose is set. In this case,
we must report an error when the client aborts. But as said before, this event
can be ignored. So to be short, for now, the abortonclose is broken.
In fact, it is a design problem and we have to rethink all channel's flags and
probably the conn-stream ones too. It is important to split EOS and EOM to not
loose information anymore. But it is not a small job and the refactoring will be
far from straightforward.
So for now, temporary flags are introduced. When the last read is received, the
flag CS_FL_READ_NULL is set on the conn-stream. This way, we can set the flag
SI_FL_READ_NULL on the stream interface. Both flags are persistant. And to be
sure to wake the stream, the event CF_READ_NULL is reported. So the stream will
always have the chance to handle the last read.
This patch must be backported to 1.9 because it will be used by another patch to
fix the option abortonclose.
