2008/1/19, Linus Torvalds <[EMAIL PROTECTED]>: > > > On Sat, 19 Jan 2008, Anton Salikhmetov wrote: > > > > Before using pte_wrprotect() the vma_wrprotect() routine uses the > > pte_offset_map_lock() macro to get the PTE and to acquire the ptl > > spinlock. Why did you say that this code was not SMP-safe? It should > > be atomic, I think. > > It's atomic WITH RESPECT TO OTHER PEOPLE WHO GET THE LOCK. > > Guess how much another x86 CPU cares when it sets the accessed bit in > hardware?
Thank you very much for taking part in this discussion. Personally, it's very important to me. But I'm not sure that I understand which bit can be lost. Please let me explain. The logic for my vma_wrprotect() routine was taken from the page_check_address() function in mm/rmap.c. Here is a code snippet of the latter function: pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) return NULL; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return NULL; pmd = pmd_offset(pud, address); if (!pmd_present(*pmd)) return NULL; pte = pte_offset_map(pmd, address); /* Make a quick check before getting the lock */ if (!pte_present(*pte)) { pte_unmap(pte); return NULL; } ptl = pte_lockptr(mm, pmd); spin_lock(ptl); if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) { *ptlp = ptl; return pte; } pte_unmap_unlock(pte, ptl); The page_check_address() function is called from the page_mkclean_one() routine as follows: pte = page_check_address(page, mm, address, &ptl); if (!pte) goto out; if (pte_dirty(*pte) || pte_write(*pte)) { pte_t entry; flush_cache_page(vma, address, pte_pfn(*pte)); entry = ptep_clear_flush(vma, address, pte); entry = pte_wrprotect(entry); entry = pte_mkclean(entry); set_pte_at(mm, address, pte, entry); ret = 1; } pte_unmap_unlock(pte, ptl); The write-protection of the PTE is done using the pte_wrprotect() entity. I intended to do the same during msync() with MS_ASYNC. I understand that I'm taking a risk of looking a complete idiot now, however I don't see any difference between the two situations. I presumed that the code in mm/rmap.c was absolutely correct, that's why I basically reused the design. > > > The POSIX standard requires the ctime and mtime stamps to be updated > > not later than at the second call to msync() with the MS_ASYNC flag. > > .. and that is no excuse for bad code. > > Linus > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/