The flush cells process can close a channel if the connection write fails but
still return that it flushed at least one cell. This is due because the error
is not propagated up the call stack so there is no way of knowing if the flush
actually was successful or not.
Because this would require an important refactoring touching multiple
subsystems, this patch is a bandaid to avoid the KIST scheduler to handle
closed channel in its loop.
Bandaid on #23751.
Signed-off-by: David Goulet <dgoulet@torproject.org>
When a BUG() occurs, this macro will print extra information about the state
of the scheduler and the given channel if any. This will help us greatly to
fix future bugs in the scheduler especially when they occur rarely.
Fixes#23753
Signed-off-by: David Goulet <dgoulet@torproject.org>
Because our monotonic time interface doesn't play well with value set to 0,
always initialize to now() the scheduler_last_run at init() of the KIST
scheduler.
Fixes#23696
Signed-off-by: David Goulet <dgoulet@torproject.org>
When a channel is scheduled and flush cells returns 0 that is no cells to
flush, we flag it back in waiting for cells so it doesn't get stuck in a
possible infinite loop.
It has been observed on moria1 where a closed channel end up in the scheduler
where the flush process returned 0 cells but it was ultimately kept in the
scheduling loop forever. We suspect that this is due to a more deeper problem
in tor where the channel_more_to_flush() is actually looking at the wrong
queue and was returning 1 for an empty channel thus putting the channel in the
"Case 4" of the scheduler which is to go back in pending state thus
re-considered at the next iteration.
This is a fix that allows the KIST scheduler to recover properly from a not
entirelly diagnosed problem in tor.
Fixes#23676
Signed-off-by: David Goulet <dgoulet@torproject.org>
When the KIST schedule() is called, it computes a diff value between the last
scheduler run and the current monotonic time. If tha value is below the run
interval, the libevent even is updated else the event is run.
It turned out that casting to int32_t the returned int64_t value for the very
first scheduler run (which is set to 0) was creating an overflow on the 32 bit
value leading to adding the event with a gigantic usec value. The scheduler
was simply never running for a while.
First of all, a BUG() is added for a diff value < 0 because if the time is
really monotonic, we should never have a now time that is lower than the last
scheduler run time. And we will try to recover with a diff value to 0.
Second, the diff value is changed to int64_t so we avoid this "bootstrap
overflow" and future casting overflow problems.
Fixes#23558
Signed-off-by: David Goulet <dgoulet@torproject.org>
Otherwise integer overflows can happen. Remember, doing a i32xi32
multiply doesn't actually produce a 64-bit output. You need to do
i64xi32 or i64xi64.
Coverity found this as CID 1417753
Each type of scheduler implements its own static scheduler_t object and
returns a reference to it.
This commit also makes it a const pointer that is it can only change inside
the scheduler type subsystem but not outside for extra protection.
Signed-off-by: David Goulet <dgoulet@torproject.org>
Instead, add wrappers to do the needed action the different scheduler needs
with the libevent object.
Signed-off-by: David Goulet <dgoulet@torproject.org>
This option is a list of possible scheduler type tor can use ordered by
priority. Its default value is "KIST,KISTLite,Vanilla" which means that KIST
will be used first and if unavailable will fallback to KISTLite and so on.
Signed-off-by: David Goulet <dgoulet@torproject.org>
It is possible that tor was compiled with KIST support but the running kernel
has no support for it. In that case, fallback to a naive approach and flag
that we have no kernel support.
At this commit, if the kernel support is disabled, there are no ways to come
back from it other than restarting tor with a kernel that supporst KIST.
Signed-off-by: David Goulet <dgoulet@torproject.org>
Add a detection for the KIST scheduler in our build system and set
HAVE_KIST_SUPPORT if available.
Adapt the should use kist function with this new compile option.
Signed-off-by: David Goulet <dgoulet@torproject.org>
- HT_FOREACH_FN defined in an additional place because nickm did that
in an old kist prototype
- Make channel_more_to_flush mockable for future sched tests
- Add empty scheduler_{vanilla,kist}.c files and put in include.am
Signed-off-by: David Goulet <dgoulet@torproject.org>
