On 08/11/2015 11:26 PM, Kirill A. Shutemov wrote: > On Tue, Aug 11, 2015 at 07:17:12PM +0300, Boaz Harrosh wrote: >> On 08/11/2015 06:28 PM, Kirill A. Shutemov wrote: >>> We also used lock_page() to make sure we shoot out all pages as we don't >>> exclude page faults during truncate. Consider this race: >>> >>> <fault> <truncate> >>> get_block >>> check i_size >>> update i_size >>> unmap >>> setup pte >>> >> >> Please consider this senario then: >> >> <fault> <truncate> >> read_lock(inode) >> >> get_block >> check i_size >> >> read_unlock(inode) >> >> write_lock(inode) >> >> update i_size >> * remove allocated blocks >> unmap >> >> write_unlock(inode) >> >> setup pte >> >> IS what you suppose to do in xfs > > Do you realize that you describe a race? :-P > > Exactly in this scenario pfn your pte point to is not belong to the file > anymore. Have fun. > Sorry yes I have written it wrong, I have now returned to read the actual code and the setup pte part is also part of the read lock inside the fault handler before the release of the r_lock. Da of course it is, it is the page_fault handler that does the vm_insert_mixed(vma,,pfn) and in the case of concurrent faults the second call to vm_insert_mixed will return -EBUSY which means all is well. So the only thing left is the fault-to-fault zero-the-page race as Matthew described and as Dave and me think we can make this part of the FS's get_block where it is more natural. Thanks Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
