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Is expand_stack buggy wrt locked_vm?

DISCUSSION Kanoj Sarcar 1 participant 1 message Jun 1, 1999 Memory management

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Kanoj Sarcar

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I think there might be a problem with the way expand_stack updates locked_vm.

Assume the kernel is trying to copyout some amount(512b) of data into the user's stack, and the underlying pages are not yet allocated, and the stack is marked VM_LOCKED. The page fault will trigger an expand_stack, which will update the locked_vm by an amount depending on where the kernel is trying to write out the data. Back in the fault handling code, handle_mm_fault will allocate just one page and be done. So, although the process has incremented its number of locked pages by 1, expand_stack has updated locked_vm by a possibly bigger amount.

I think the right fix is for expand_stack to fault in all the intermediate pages, by something like

	if (vma->vm_flags & VM_LOCKED) {
		make_pages_present(address, old vma->vm_start);
	}

Comments?

Kanoj
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