Since `s_mm_lock` is a RecursiveSpinlock, if a kernel thread gets
preempted while accidentally hold the lock during switch_context,
another thread running on the same processor could end up manipulating
the state of the memory manager even though they should not be able to.
It will just bump the recursion count and keep going.
This appears to be the root cause of weird bugs like: #7359
Where page protection magically appears to be wrong during execution.
To avoid these cases lets guard this specific unfortunate case and make
sure it can never go unnoticed ever again.
The assert was Tom's idea to help debug this, so I am going to tag him
as co-author of this commit.
Co-Authored-By: Tom <tomut@yahoo.com>
By constraining two implementations, the compiler will select the best
fitting one. All this will require is duplicating the implementation and
simplifying for the `void` case.
This constraining also informs both the caller and compiler by passing
the callback parameter types as part of the constraint
(e.g.: `IterationFunction<int>`).
Some `for_each` functions in LibELF only take functions which return
`void`. This is a minimal correctness check, as it removes one way for a
function to incompletely do something.
There seems to be a possible idiom where inside a lambda, a `return;` is
the same as `continue;` in a for-loop.
This updates the profiling subsystem to use a separate timer to
trigger CPU sampling. This timer has a higher resolution (1000Hz)
and is independent from the scheduler. At a later time the
resolution could even be made configurable with an argument for
sys$profiling_enable() - but not today.
The variety of checks for Processor::id() == 0 could use some assistance
in the readability department. This change adds a new function to
represent this check, and replaces the comparison everywhere it's used.
This solves a problem where checking whether a thread is an idle
thread may require iterating all processors if it is not the idle
thread of the current processor.
This turns the perfcore format into more a log than it was before,
which lets us properly log process, thread and region
creation/destruction. This also makes it unnecessary to dump the
process' regions every time it is scheduled like we did before.
Incidentally this also fixes 'profile -c' because we previously ended
up incorrectly dumping the parent's region map into the profile data.
Log-based mmap support enables profiling shared libraries which
are loaded at runtime, e.g. via dlopen().
This enables profiling both the parent and child process for
programs which use execve(). Previously we'd discard the profiling
data for the old process.
The Profiler tool has been updated to not treat thread IDs as
process IDs anymore. This enables support for processes with more
than one thread. Also, there's a new widget to filter which
process should be displayed.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Pressing this combo will dump a list of all threads and their state
to the debug console.
This might be useful to figure out why the system is not responding.
This should allow creating intrusive lists that have smart pointers,
while remaining free (compared to the impl before this commit) when
holding raw pointers :^)
As a sidenote, this also adds a `RawPtr<T>` type, which is just
equivalent to `T*`.
Note that this does not actually use such functionality, but is only
expected to pave the way for #6369, to replace NonnullRefPtrVector<T>
with intrusive lists.
As it is with zero-cost things, this makes the interface a bit less nice
by requiring the type name of what an `IntrusiveListNode` holds (and
optionally its container, if not RawPtr), and also requiring the type of
the container (normally `RawPtr`) on the `IntrusiveList` instance.
The perfcore file format was previously limited to a single process
since the pid/executable/regions data was top-level in the JSON.
This patch moves the process-specific data into a top-level array
named "processes" and we now add entries for each process that has
been sampled during the profile run.
This makes it possible to see samples from multiple threads when
viewing a perfcore file with Profiler. This is extremely cool! :^)
The superuser can now call sys$profiling_enable() with PID -1 to enable
profiling of all running threads in the system. The perf events are
collected in a global PerformanceEventBuffer (currently 32 MiB in size.)
The events can be accessed via /proc/profile
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
There's no real system here, I just added it to various functions
that I don't believe we ever want to call after initialization
has finished.
With these changes, we're able to unmap 60 KiB of kernel text
after init. :^)
This allows us to get rid of the thread lists in SchedulerData.
Also, instead of iterating over all threads to find a thread by id,
just use a lookup table. In the rare case of having to iterate over
all threads, just iterate the lookup table.
Rather than walking all Thread instances and putting them into
a vector to be sorted by priority, queue them into priority sorted
linked lists as soon as they become ready to be executed.
Attempt to wake idle processors to get threads to be scheduled more quickly.
We don't want to wait until the next timer tick if we have processors that
aren't doing anything.
This eliminates the window between calling Processor::current and
the member function where a thread could be moved to another
processor. This is generally not as big of a concern as with
Processor::current_thread, but also slightly more light weight.
Change Thread::current to be a static function and read using the fs
register, which eliminates a window between Processor::current()
returning and calling a function on it, which can trigger preemption
and a move to a different processor, which then causes operating
on the wrong object.
This allows us to determine what the previous mode (user or kernel)
was, e.g. in the timer interrupt. This is used e.g. to determine
whether a signal handler should be set up.
Fixes#5096
These changes are arbitrarily divided into multiple commits to make it
easier to find potentially introduced bugs with git bisect.
This commit touches some dbg() calls which are enclosed in macros. This
should be fine because with the new constexpr stuff, we ensure that the
stuff actually compiles.
This patch merges the profiling functionality in the kernel with the
performance events mechanism. A profiler sample is now just another
perf event, rather than a dedicated thing.
Since perf events were already per-process, this now makes profiling
per-process as well.
Processes with perf events would already write out a perfcore.PID file
to the current directory on death, but since we may want to profile
a process and then let it continue running, recorded perf events can
now be accessed at any time via /proc/PID/perf_events.
This patch also adds information about process memory regions to the
perfcore JSON format. This removes the need to supply a core dump to
the Profiler app for symbolication, and so the "profiler coredump"
mechanism is removed entirely.
There's still a hard limit of 4MB worth of perf events per process,
so this is by no means a perfect final design, but it's a nice step
forward for both simplicity and stability.
Fixes#4848Fixes#4849
This is a crude protection against IOPL elevation attacks. If for
any reason we find ourselves about to switch to a user mode thread
with IOPL != 0, we'll now simply panic the kernel.
If this happens, it basically means that something tricked the kernel
into incorrectly modifying the IOPL of a thread, so it's no longer
safe to trust the kernel anyway.
This implements a number of changes related to time:
* If a HPET is present, it is now used only as a system timer, unless
the Local APIC timer is used (in which case the HPET timer will not
trigger any interrupts at all).
* If a HPET is present, the current time can now be as accurate as the
chip can be, independently from the system timer. We now query the
HPET main counter for the current time in CPU #0's system timer
interrupt, and use that as a base line. If a high precision time is
queried, that base line is used in combination with quering the HPET
timer directly, which should give a much more accurate time stamp at
the expense of more overhead. For faster time stamps, the more coarse
value based on the last interrupt will be returned. This also means
that any missed interrupts should not cause the time to drift.
* The default system interrupt rate is reduced to about 250 per second.
* Fix calculation of Thread CPU usage by using the amount of ticks they
used rather than the number of times a context switch happened.
* Implement CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE and use it
for most cases where precise timestamps are not needed.
Problem:
- `(void)` simply casts the expression to void. This is understood to
indicate that it is ignored, but this is really a compiler trick to
get the compiler to not generate a warning.
Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.
Note:
- Functions taking a `(void)` argument list have also been changed to
`()` because this is not needed and shows up in the same grep
command.
Fix some problems with join blocks where the joining thread block
condition was added twice, which lead to a crash when trying to
unblock that condition a second time.
Deferred block condition evaluation by File objects were also not
properly keeping the File object alive, which lead to some random
crashes and corruption problems.
Other problems were caused by the fact that the Queued state didn't
handle signals/interruptions consistently. To solve these issues we
remove this state entirely, along with Thread::wait_on and change
the WaitQueue into a BlockCondition instead.
Also, deliver signals even if there isn't going to be a context switch
to another thread.
Fixes#4336 and #4330
This changes the Thread::wait_on function to not enable interrupts
upon leaving, which caused some problems with page fault handlers
and in other situations. It may now be called from critical
sections, with interrupts enabled or disabled, and returns to the
same state.
This also requires some fixes to Lock. To aid debugging, a new
define LOCK_DEBUG is added that enables checking for Lock leaks
upon finalization of a Thread.
