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Kernel: Fix intermittent assertion failure in sys$exec()
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().
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1d4d6f16b2
commit
3012b224f0
3 changed files with 26 additions and 8 deletions
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@ -579,13 +579,16 @@ RegisterDump& Thread::get_register_dump_from_stack()
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return *(RegisterDump*)(kernel_stack_top() - sizeof(RegisterDump));
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}
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void Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vector<String> environment)
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u32 Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vector<String> environment)
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{
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auto* region = m_process.allocate_region(VirtualAddress(), default_userspace_stack_size, "Stack (Main thread)", PROT_READ | PROT_WRITE, false);
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ASSERT(region);
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region->set_stack(true);
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m_tss.esp = region->vaddr().offset(default_userspace_stack_size).get();
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u32 new_esp = region->vaddr().offset(default_userspace_stack_size).get();
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// FIXME: This is weird, we put the argument contents at the base of the stack,
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// and the argument pointers at the top? Why?
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char* stack_base = (char*)region->vaddr().get();
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int argc = arguments.size();
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char** argv = (char**)stack_base;
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@ -608,11 +611,19 @@ void Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vect
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}
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env[environment.size()] = nullptr;
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auto push_on_new_stack = [&new_esp](u32 value)
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{
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new_esp -= 4;
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u32* stack_ptr = (u32*)new_esp;
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*stack_ptr = value;
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};
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// NOTE: The stack needs to be 16-byte aligned.
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push_value_on_stack((u32)env);
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push_value_on_stack((u32)argv);
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push_value_on_stack((u32)argc);
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push_value_on_stack(0);
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push_on_new_stack((u32)env);
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push_on_new_stack((u32)argv);
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push_on_new_stack((u32)argc);
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push_on_new_stack(0);
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return new_esp;
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}
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Thread* Thread::clone(Process& process)
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