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vm_soft_fault(): Avoid inconsistent state when seeing wired page

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When we encounter a wired page that we'd have to unmap to map our newly
allocated one, we need to get rid of the latter before unlocking
everything and waiting for the wired page. Otherwise we'd leave things
in an inconsistent state (a page from an upper cache shadowing a mapped
page from a lower cache).
This commit is contained in:
Ingo Weinhold 2014-10-29 02:34:56 +01:00
parent 699b57307e
commit 8ef857d85c
1 changed files with 15 additions and 1 deletions
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16
src/system/kernel/vm/vm.cpp
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@ -4342,6 +4342,7 @@ struct PageFaultContext {
// return values
vm_page* page;
bool restart;
bool pageAllocated;
PageFaultContext(VMAddressSpace* addressSpace, bool isWrite)
@ -4364,6 +4365,7 @@ struct PageFaultContext {
this->cacheOffset = cacheOffset;
page = NULL;
restart = false;
pageAllocated = false;
cacheChainLocker.SetTo(topCache);
}
@ -4483,6 +4485,7 @@ fault_get_page(PageFaultContext& context)
// insert the new page into our cache
cache->InsertPage(page, context.cacheOffset);
context.pageAllocated = true;
} else if (page->Cache() != context.topCache && context.isWrite) {
// We have a page that has the data we want, but in the wrong cache
// object so we need to copy it and stick it into the top cache.
@ -4508,6 +4511,7 @@ fault_get_page(PageFaultContext& context)
// insert the new page into our cache
context.topCache->InsertPage(page, context.cacheOffset);
context.pageAllocated = true;
} else
DEBUG_PAGE_ACCESS_START(page);
@ -4682,7 +4686,17 @@ vm_soft_fault(VMAddressSpace* addressSpace, addr_t originalAddress,
if (area->AddWaiterIfWired(&waiter, address, B_PAGE_SIZE,
wiredRange)) {
// unlock everything and wait
DEBUG_PAGE_ACCESS_END(context.page);
if (context.pageAllocated) {
// ... but since we allocated a page and inserted it into
// the top cache, remove and free it first. Otherwise we'd
// have a page from a lower cache mapped while an upper
// cache has a page that would shadow it.
context.topCache->RemovePage(context.page);
vm_page_free_etc(context.topCache, context.page,
&context.reservation);
} else
DEBUG_PAGE_ACCESS_END(context.page);
context.UnlockAll();
waiter.waitEntry.Wait();
continue;