Nick Piggin <npiggin@xxxxxxx> writes:
> On Tue, Oct 28, 2008 at 05:11:02PM -0400, Jeff Moyer wrote:
>> Nick Piggin <npiggin@xxxxxxx> writes:
>> > Index: linux-2.6/mm/filemap.c
>> > ===================================================================
>> > --- linux-2.6.orig/mm/filemap.c 2008-10-03 11:21:31.000000000 +1000
>> > +++ linux-2.6/mm/filemap.c 2008-10-03 12:00:17.000000000 +1000
>> > @@ -1304,11 +1304,8 @@ generic_file_aio_read(struct kiocb *iocb
>> > goto out; /* skip atime */
>> > size = i_size_read(inode);
>> > if (pos < size) {
>> > - retval = filemap_write_and_wait(mapping);
>> > - if (!retval) {
>> > - retval = mapping->a_ops->direct_IO(READ, iocb,
>> > + retval = mapping->a_ops->direct_IO(READ, iocb,
>> > iov, pos, nr_segs);
>> > - }
>>
>> So why is it safe to get rid of this? Can't this result in reading
>> stale data from disk?
>
> AFAIKS, __blockdev_direct_IO is doing the same thing for us, when it
> encounters a READ. I should have documented this change. This is one
> thing I'm not *quite* sure of there might be a path do the block device
> that I haven't considered, and which does not do the sync...
Well, that's if dio_lock_type != DIO_NO_LOCKING. cscope shows the
following callers of blockdev_direct_IO_no_locking:
gfs2_direct_IO
ocfs2_direct_IO
xfs_vm_direct_IO
and of course
blkdev_direct_IO
I can't say whether all of these callers are safe. They certainly don't
appear to be safe to me.
Cheers,
Jeff
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