KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> writes: >> Hello, >> >> Thank you revisit this. But as far as my remember is correct, this issue is NOT >> unaligned access issue. It's just get_user_pages(_fast) vs fork race issue. i.e. >> DIRECT_IO w/ multi thread process should not use fork(). > > The problem is, fork (and its COW logic) assume new access makes cow break, > But page table protection can't detect a DMA write. Therefore DIO may override > shared page data. Hm, I've only seen this with misaligned or multiple sub-page-sized reads in the same page. AFAIR, aligned, page-sized I/O does not get split. But, I could be wrong... Cheers, Jeff -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>