The sys$alarm() syscall has logic to cache a m_alarm_timer to avoid
allocating a new timer for every call to alarm. Unfortunately that
logic was broken, and there were conditions in which we could have
a timer allocated, but it was no longer on the timer queue, and we
would attempt to cancel that timer again resulting in an infinite
loop waiting for the timers callback to fire.
To fix this, we need to track if a timer is currently in use or not,
allowing us to avoid attempting to cancel inactive timers.
Luke and Tom did the initial investigation, I just happened to have
time to write a repro and attempt a fix, so I'm adding them as the
as co-authors of this commit.
Co-authored-by: Luke <luke.wilde@live.co.uk>
Co-authored-by: Tom <tomut@yahoo.com>
This isn't needed for Process / Thread as they only reference it
by pointer and it's already part of Kernel/Forward.h. So just include
it where the implementation needs to call it.
AnonymousVMObject::set_volatile() assumes that nobody ever calls it on
non-purgeable objects, so let's make sure we don't do that.
Also return EINVAL instead of EPERM for non-anonymous VM objects so the
error codes match.
Previously it was possible to leak the file descriptor if we error out
after allocating the first descriptor. Now we perform both fd
allocations back to back so we can handle the potential error when
processing the second fd allocation.
The way the Process::FileDescriptions::allocate() API works today means
that two callers who allocate back to back without associating a
FileDescription with the allocated FD, will receive the same FD and thus
one will stomp over the other.
Naively tracking which FileDescriptions are allocated and moving onto
the next would introduce other bugs however, as now if you "allocate"
a fd and then return early further down the control flow of the syscall
you would leak that fd.
This change modifies this behavior by tracking which descriptions are
allocated and then having an RAII type to "deallocate" the fd if the
association is not setup the end of it's scope.
This was previously used for a single debug logging statement during
memory purging. There are no remaining users of this weak pointer,
so let's get rid of it.
This patch changes the semantics of purgeable memory.
- AnonymousVMObject now has a "purgeable" flag. It can only be set when
constructing the object. (Previously, all anonymous memory was
effectively purgeable.)
- AnonymousVMObject now has a "volatile" flag. It covers the entire
range of physical pages. (Previously, we tracked ranges of volatile
pages, effectively making it a page-level concept.)
- Non-volatile objects maintain a physical page reservation via the
committed pages mechanism, to ensure full coverage for page faults.
- When an object is made volatile, it relinquishes any unused committed
pages immediately. If later made non-volatile again, we then attempt
to make a new committed pages reservation. If this fails, we return
ENOMEM to userspace.
mmap() now creates purgeable objects if passed the MAP_PURGEABLE option
together with MAP_ANONYMOUS. anon_create() memory is always purgeable.
This bug manifests it self when the caller to sys$pledge() passes valid
promises, but invalid execpromises. The code would apply the promises
and then return an error for the execpromises. This leaves the user in
a confusing state, as the promises were silently applied, but we return
an error suggesting the operation has failed.
Avoid this situation by tweaking the implementation to only apply the
promises / execpromises after all validation has occurred.
This patch greatly simplifies VMObject locking by doing two things:
1. Giving VMObject an IntrusiveList of all its mapping Region objects.
2. Removing VMObject::m_paging_lock in favor of VMObject::m_lock
Before (1), VMObject::for_each_region() was forced to acquire the
global MM lock (since it worked by walking MemoryManager's list of
all regions and checking for regions that pointed to itself.)
With each VMObject having its own list of Regions, VMObject's own
m_lock is all we need.
Before (2), page fault handlers used a separate mutex for preventing
overlapping work. This design required multiple temporary unlocks
and was generally extremely hard to reason about.
Instead, page fault handlers now use VMObject's own m_lock as well.
Depending on the values it might be difficult to figure out whether a
value is decimal or hexadecimal. So let's make this more obvious. Also
this allows copying and pasting those numbers into GNOME calculator and
probably also other apps which auto-detect the base.
Advisory locks don't actually prevent other processes from writing to
the file, but they do prevent other processes looking to acquire and
advisory lock on the file.
This implementation currently only adds non-blocking locks, which are
all I need for now.
Before we start disabling acquisition of the big process lock for
specific syscalls, make sure to document and assert that all the
lock is held during all syscalls.
The entire process is not needed, just require the user to pass in the
Space. Also provide no_lock variant to use when you already have the
VM/Space lock acquired, to avoid unnecessary recursive spinlock
acquisitions.
The non CPU specific code of the kernel shouldn't need to deal with
architecture specific registers, and should instead deal with an
abstract view of the machine. This allows us to remove a variety of
architecture specific ifdefs and helps keep the code slightly more
portable.
We do this by exposing the abstract representation of instruction
pointer, stack pointer, base pointer, return register, etc on the
RegisterState struct.
We should never request a regions removal that we don't currently
own. We currently assert this everywhere else by all callers.
Instead lets just push the assert down into the RedBlackTree removal
and assume that we will always successfully remove the region.
Thread::yield_and_release_relock_big_lock releases the big lock, yields
and then relocks the big lock.
Thread::yield_assuming_not_holding_big_lock yields assuming the big
lock is not being held.
We leak a ref() onto every user process when constructing them,
either via Process::create_user_process(), or via Process::sys$fork().
This ref() is balanced by a corresponding unref() in
Thread::WaitBlockCondition::finalize().
Since kernel processes don't have a leaked ref() on them, this led to
an extra Process::unref() on kernel processes during finalization.
This happened during every boot, with the `init_stage2` process.
Found by turning off kfree() scrubbing. :^)
There appears to be no reason why the process registration needs
to happen under the space spin lock. As the first thread is not started
yet it should be completely uncontested, but it's still bad practice.
The System V ABI for both x86 and x86_64 requires that the stack pointer
is 16-byte aligned on entry. Previously we did not align the stack
pointer properly.
As far as "main" was concerned the stack alignment was correct even
without this patch due to how the C++ _start function and the kernel
interacted, i.e. the kernel misaligned the stack as far as the ABI
was concerned but that misalignment (read: it was properly aligned for
a regular function call - but misaligned in terms of what the ABI
dictates) was actually expected by our _start function.
`.text` segments with non-aligned offsets had their lengths applied to
the first page's base address. This meant that in some cases the last
PAGE_SIZE - 1 bytes weren't mapped. Previously, it did not cause any
problems as the GNU ld insists on aligning everything; but that's not
the case with the LLVM toolchain.
This replaces all uses of LexicalPath in the Kernel with the functions
from KLexicalPath. This also allows the Kernel to stop including
AK::LexicalPath.
