On 2016/7/9 0:13, Catalin Marinas wrote: > On Fri, Jul 08, 2016 at 11:24:26PM +0800, Leizhen (ThunderTown) wrote: >> On 2016/7/8 21:54, Catalin Marinas wrote: >>> On Fri, Jul 08, 2016 at 11:36:57AM +0800, Leizhen (ThunderTown) wrote: >>>> On 2016/7/7 23:37, Catalin Marinas wrote: >>>>> On Thu, Jul 07, 2016 at 08:09:04PM +0800, Zhen Lei wrote: >>>>>> At present, PG_dcache_clean is only cleared when the related huge page >>>>>> is about to be freed. But sometimes, there maybe a process is in charge >>>>>> to copy binary codes into a shared memory, and notifies other processes >>>>>> to execute base on that. For the first time, there is no problem, because >>>>>> the default value of page->flags is PG_dcache_clean cleared. So the cache >>>>>> will be maintained at the time of set_pte_at for other processes. But if >>>>>> the content of the shared memory have been updated again, there is no >>>>>> cache operations, because the PG_dcache_clean is still set. >>>>>> >>>>>> For example: >>>>>> Process A >>>>>> open a hugetlbfs file >>>>>> mmap it as a shared memory >>>>>> copy some binary codes into it >>>>>> munmap >>>>>> >>>>>> Process B >>>>>> open the hugetlbfs file >>>>>> mmap it as a shared memory, executable >>>>>> invoke the functions in the shared memory >>>>>> munmap >>>>>> >>>>>> repeat the above steps. >>>>> >>>>> Does this work as you would expect with small pages (and for example >>>>> shared file mmap)? I don't want to have a different behaviour between >>>>> small and huge pages. >>>> >>>> The small pages also have this problem, I will try to fix it too. > [...] >>> If both cases need solving, we might better move the fix in the >>> __sync_icache_dcache() function. Untested: >> >> At first I also want to fix it as below. But I'm not sure which time the >> PageDirty >> will be cleared, and if two or more processes mmap it as executable, cache >> operations >> will be duplicated. At present, I really have not found any good place to >> clear >> PG_dcache_clean. So the below modification may be the best choice, concisely >> and clearly. >> >>> ------------8<---------------- >>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c >>> index dbd12ea8ce68..c753fa804165 100644 >>> --- a/arch/arm64/mm/flush.c >>> +++ b/arch/arm64/mm/flush.c >>> @@ -75,7 +75,8 @@ void __sync_icache_dcache(pte_t pte, unsigned long addr) >>> if (!page_mapping(page)) >>> return; >>> >>> - if (!test_and_set_bit(PG_dcache_clean, &page->flags)) >>> + if (!test_and_set_bit(PG_dcache_clean, &page->flags) || >>> + PageDirty(page)) >>> sync_icache_aliases(page_address(page), >>> PAGE_SIZE << compound_order(page)); >>> else if (icache_is_aivivt()) >>> ----------------8<--------------------- >>> >>> BTW, can you make your tests (source) available somewhere? >> >> Both cases worked well with this patch. > > Now I'm even more confused ;). IIUC, after an msync() in user space we > should flush the pages to disk via write_cache_pages(). This function > calls clear_page_dirty_for_io() after which PageDirty() is no longer > true. I can't tell how a subsequent mmap() can see the written pages as > dirty. >
As my tracing, both cases invoked empty function. int vfs_fsync_range(struct file *file, loff_t start, loff_t end, int datasync) ...... return file->f_op->fsync(file, start, end, datasync); } const struct file_operations hugetlbfs_file_operations = { .fsync = noop_fsync, static const struct file_operations shmem_file_operations = { .mmap = shmem_mmap, #ifdef CONFIG_TMPFS .fsync = noop_fsync,