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Kernel: Don't hog VMObject lock when remapping a region page

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We really only need the VMObject lock when accessing the physical pages
array, so once we have a strong pointer to the physical page we want to
remap, we can give up the VMObject lock.

This fixes a deadlock I encountered while building DOOM on SMP.
This commit is contained in:
Andreas Kling 2022-08-18 18:54:36 +02:00
parent 10399a258f
commit b560442fe1
2 changed files with 53 additions and 42 deletions
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92
Kernel/Memory/Region.cpp
View file

@ -202,10 +202,9 @@ ErrorOr<void> Region::set_should_cow(size_t page_index, bool cow)
return {};
}
bool Region::map_individual_page_impl(size_t page_index)
bool Region::map_individual_page_impl(size_t page_index, RefPtr<PhysicalPage> page)
{
VERIFY(m_page_directory->get_lock().is_locked_by_current_processor());
VERIFY(s_mm_lock.is_locked_by_current_processor());
auto page_vaddr = vaddr_from_page_index(page_index);
@ -214,43 +213,53 @@ bool Region::map_individual_page_impl(size_t page_index)
PANIC("About to map mmap'ed page at a kernel address");
}
SpinlockLocker lock(s_mm_lock);
auto* pte = MM.ensure_pte(*m_page_directory, page_vaddr);
if (!pte)
return false;
auto* page = physical_page(page_index);
if (!page || (!is_readable() && !is_writable())) {
pte->clear();
} else {
pte->set_cache_disabled(!m_cacheable);
pte->set_physical_page_base(page->paddr().get());
pte->set_present(true);
if (page->is_shared_zero_page() || page->is_lazy_committed_page() || should_cow(page_index))
pte->set_writable(false);
else
pte->set_writable(is_writable());
if (Processor::current().has_nx())
pte->set_execute_disabled(!is_executable());
if (Processor::current().has_pat())
pte->set_pat(is_write_combine());
pte->set_user_allowed(user_allowed);
return true;
}
pte->set_cache_disabled(!m_cacheable);
pte->set_physical_page_base(page->paddr().get());
pte->set_present(true);
if (page->is_shared_zero_page() || page->is_lazy_committed_page() || should_cow(page_index))
pte->set_writable(false);
else
pte->set_writable(is_writable());
if (Processor::current().has_nx())
pte->set_execute_disabled(!is_executable());
if (Processor::current().has_pat())
pte->set_pat(is_write_combine());
pte->set_user_allowed(user_allowed);
return true;
}
bool Region::remap_vmobject_page(size_t page_index, bool with_flush)
bool Region::map_individual_page_impl(size_t page_index)
{
RefPtr<PhysicalPage> page;
{
SpinlockLocker vmobject_locker(vmobject().m_lock);
page = physical_page(page_index);
}
return map_individual_page_impl(page_index, page);
}
bool Region::remap_vmobject_page(size_t page_index, NonnullRefPtr<PhysicalPage> physical_page)
{
SpinlockLocker page_lock(m_page_directory->get_lock());
SpinlockLocker mm_lock(s_mm_lock);
SpinlockLocker lock(m_vmobject->m_lock);
// NOTE: `page_index` is a VMObject page index, so first we convert it to a Region page index.
if (!translate_vmobject_page(page_index))
return false;
VERIFY(physical_page(page_index));
bool success = map_individual_page_impl(page_index);
if (with_flush)
MemoryManager::flush_tlb(m_page_directory, vaddr_from_page_index(page_index));
bool success = map_individual_page_impl(page_index, physical_page);
MemoryManager::flush_tlb(m_page_directory, vaddr_from_page_index(page_index));
return success;
}
@ -286,7 +295,6 @@ void Region::set_page_directory(PageDirectory& page_directory)
ErrorOr<void> Region::map(PageDirectory& page_directory, ShouldFlushTLB should_flush_tlb)
{
SpinlockLocker page_lock(page_directory.get_lock());
SpinlockLocker lock(s_mm_lock);
// FIXME: Find a better place for this sanity check(?)
if (is_user() && !is_shared()) {
@ -364,7 +372,7 @@ PageFaultResponse Region::handle_fault(PageFault const& fault)
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
VERIFY(m_vmobject->is_anonymous());
page_slot = static_cast<AnonymousVMObject&>(*m_vmobject).allocate_committed_page({});
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_vmobject_page(page_index_in_vmobject, *page_slot))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -403,7 +411,7 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
if (!page_slot.is_null() && !page_slot->is_shared_zero_page() && !page_slot->is_lazy_committed_page()) {
dbgln_if(PAGE_FAULT_DEBUG, "MM: zero_page() but page already present. Fine with me!");
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_vmobject_page(page_index_in_vmobject, *page_slot))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -426,7 +434,7 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
dbgln_if(PAGE_FAULT_DEBUG, " >> ALLOCATED {}", page_slot->paddr());
}
if (!remap_vmobject_page(page_index_in_vmobject)) {
if (!remap_vmobject_page(page_index_in_vmobject, *page_slot)) {
dmesgln("MM: handle_zero_fault was unable to allocate a page table to map {}", page_slot);
return PageFaultResponse::OutOfMemory;
}
@ -445,7 +453,7 @@ PageFaultResponse Region::handle_cow_fault(size_t page_index_in_region)
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
auto response = reinterpret_cast<AnonymousVMObject&>(vmobject()).handle_cow_fault(page_index_in_vmobject, vaddr().offset(page_index_in_region * PAGE_SIZE));
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_vmobject_page(page_index_in_vmobject, *vmobject().physical_pages()[page_index_in_vmobject]))
return PageFaultResponse::OutOfMemory;
return response;
}
@ -467,7 +475,7 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_slot.is_null()) {
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else before reading, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_vmobject_page(page_index_in_vmobject, *vmobject_physical_page_slot))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -511,21 +519,23 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
MM.unquickmap_page();
}
// NOTE: The VMObject lock is required when manipulating the VMObject's physical page slot.
SpinlockLocker locker(inode_vmobject.m_lock);
{
// NOTE: The VMObject lock is required when manipulating the VMObject's physical page slot.
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_slot.is_null()) {
// Someone else faulted in this page while we were reading from the inode.
// No harm done (other than some duplicate work), remap the page here and return.
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
if (!vmobject_physical_page_slot.is_null()) {
// Someone else faulted in this page while we were reading from the inode.
// No harm done (other than some duplicate work), remap the page here and return.
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject, *vmobject_physical_page_slot))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
vmobject_physical_page_slot = new_physical_page;
}
vmobject_physical_page_slot = move(new_physical_page);
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_vmobject_page(page_index_in_vmobject, *vmobject_physical_page_slot))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;