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Kernel: Fix intermittent assertion failure in sys$exec()

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While setting up the main thread stack for a new process, we'd incur
some zero-fill page faults. This was to be expected, since we allocate
a huge stack but lazily populate it with physical pages.

The problem is that page fault handlers may enable interrupts in order
to grab a VMObject lock (or to page in from an inode.)

During exec(), a process is reorganizing itself and will be in a very
unrunnable state if the scheduler should interrupt it and then later
ask it to run again. Which is exactly what happens if the process gets
pre-empted while the new stack's zero-fill page fault grabs the lock.

This patch fixes the issue by creating new main thread stacks before
disabling interrupts and going into the critical part of exec().
This commit is contained in:
Andreas Kling 2019-12-18 23:03:23 +01:00
parent 1d4d6f16b2
commit 3012b224f0
3 changed files with 26 additions and 8 deletions
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23
Kernel/Thread.cpp
View file

@ -579,13 +579,16 @@ RegisterDump& Thread::get_register_dump_from_stack()
return *(RegisterDump*)(kernel_stack_top() - sizeof(RegisterDump));
}
void Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vector<String> environment)
u32 Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vector<String> environment)
{
auto* region = m_process.allocate_region(VirtualAddress(), default_userspace_stack_size, "Stack (Main thread)", PROT_READ | PROT_WRITE, false);
ASSERT(region);
region->set_stack(true);
m_tss.esp = region->vaddr().offset(default_userspace_stack_size).get();
u32 new_esp = region->vaddr().offset(default_userspace_stack_size).get();
// FIXME: This is weird, we put the argument contents at the base of the stack,
// and the argument pointers at the top? Why?
char* stack_base = (char*)region->vaddr().get();
int argc = arguments.size();
char** argv = (char**)stack_base;
@ -608,11 +611,19 @@ void Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vect
}
env[environment.size()] = nullptr;
auto push_on_new_stack = [&new_esp](u32 value)
{
new_esp -= 4;
u32* stack_ptr = (u32*)new_esp;
*stack_ptr = value;
};
// NOTE: The stack needs to be 16-byte aligned.
push_value_on_stack((u32)env);
push_value_on_stack((u32)argv);
push_value_on_stack((u32)argc);
push_value_on_stack(0);
push_on_new_stack((u32)env);
push_on_new_stack((u32)argv);
push_on_new_stack((u32)argc);
push_on_new_stack(0);
return new_esp;
}
Thread* Thread::clone(Process& process)