Messages in this thread Patch in this message | | | Date | Tue, 19 Feb 2002 23:05:23 +0100 | From | Juan Cespedes <> | Subject | The ptrace() bug... |
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Version 2.2.0 (at least) to 2.4.14-pre7 contain this line in mm/memory.c:copy_page_range:
unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
Version 2.4.14-pre8 and later changed this line with:
unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_WRITE)) == VM_WRITE;
This line decides if copy-on-write should be active in a vm_area just after a fork. The latter is more correct IMHO, with one exception: it breaks ptraced programs, because programs been ptraced can see their pages modified without having the VM_WRITE flag, and this causes that both the parent and the child may see their pages changed (copy-on-write doesn't work).
Reverting that one-line patch solves many problems for me and I think there are no other side-effects...
Could it be included in 2.4?
Thanks,
<====================================================================> --- old/linux-2.4.17/mm/memory.c Fri Dec 21 18:42:05 2001 +++ linux-2.4.17/mm/memory.c Sun Feb 17 20:38:20 2002 @@ -177,7 +177,7 @@ pgd_t * src_pgd, * dst_pgd; unsigned long address = vma->vm_start; unsigned long end = vma->vm_end; - unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_WRITE)) == VM_WRITE; + unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; src_pgd = pgd_offset(src, address)-1; dst_pgd = pgd_offset(dst, address)-1; <====================================================================> -- .+'''+. .+'''+. .+'''+. .+'''+. .+'' Juan Cespedes / \ / \ cespedes@TheHackers.org .+' `+...+' `+...+' `+...+' `+...+' - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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