2011/3/23 Jeff Layton <jlayton@xxxxxxxxxx>:
> On Wed, 23 Mar 2011 12:32:03 -0500
> Steve French <smfrench@xxxxxxxxx> wrote:
>
>> On Wed, Mar 23, 2011 at 11:14 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>> > On Wed, 23 Mar 2011 12:27:31 +0300
>> > Pavel Shilovsky <piastry@xxxxxxxxxxx> wrote:
>> >
>> >> 2011/3/23 Steve French <smfrench@xxxxxxxxx>:
>> >> > Pavel,
>> >> > Jeff and I talked about invalidate_mapping and its uses this
>> >> > afternoon. A few comments:
>> >> > 1) Take a look at what happens on filemap_fdatawait call in
>> >> > invalidate_mapping to see if it makes sense to return errors through
>> >> > back to some of the callers of invalidate_mapping, in particular,
>> >> > strict_fsync. If we can't write out the file data (ENOSPC, or host
>> >> > down etc.), we want to make sure that the return code gets sent back
>> >> > on any calls that can reasonably expect such an error.
>> >>
>> >> vfs_fsync_range has already done filemap_fdatawait call - so, in this
>> >> case there is no need to do it again in cifs_invalidate_mapping. The
>> >> only reason for calling this is to invalidate_inode_pages2 but any
>> >> error there shouldn't affect fsync behavior, as I think.
>> >>
>> >> > 2) If invalidate_inode_pages2 fails (e.g. with EBUSY, because one of
>> >> > the pages couldn't be freed from the mapping because it just got
>> >> > redirtied right after we flushed it the line before) we set the
>> >> > mapping to invalid but don't check
>> >> > cifs_i->invalid_mapping
>> >> > in many places. Should we add checks for cifs_i->invalid_mapping in
>> >> > more places?
>> >>
>> >> The one place where we should add such a check is read call, but it
>> >> needs cifs_revalidate_file instead (that I am going to provide next)
>> >> before generic_file_aio_read. In this case cifs_revalidate will check
>> >> for invalid_mapping and needs to return a error if we could not
>> >> invalidate all inode pages in cifs_invalidate_mapping (because it
>> >> returns wrong data to the read call). But as you noticed lseek
>> >> shouldn't think about this error and it uses cifs_revalidate_file too.
>> >>
>> >> So, we may add extra check for -EBUSY error code in callers of
>> >> cifs_revalidate_{dentry,file} and cifs_invaliadate_mapping and
>> >> separate them into two groups:
>> >> 1) that aware about -EBUSY error code and return a error the it's caller.
>> >> these are: cifs_d_revalidate, cifs_file_aio_read (future
>> >> implementation), cifs_file_strict_mmap.
>> >> 2) that doesn't aware about it and return ok in this case.
>> >> these are: cifs_getattrs, cifs_lseek, cifs_fsync.
>> >>
>> >> Thoughts?
>> >>
>> >
>> > The main reason I think we need to reconsider that error is that I
>> > spent several months tracking down a rather nasty data corruption bug
>> > relating to mmap on NFS in RHEL5 a few years ago:
>> >
>> > https://bugzilla.redhat.com/show_bug.cgi?id=435291
>> >
>> > Part of the problem there was that the NFS client ignored the return
>> > code from invalidate_inode_pages2. The other part of the problem was a
>> > lack of synchronization between mmap calls and the page fault handler.
>> >
>> > Needless to say, this was not a fun problem to track down. I think you
>> > need to be very careful about ignoring errors from
>> > invalidate_inode_pages2 and think carefully about what a failure there
>> > means for all cases.
>>
>> I agree - need to be careful, but IIRC the NFS problem would be that
>> it has a launder_page method which is returning an error through
>> invalidate_inode_pages2 while in the cifs case the data is forced to
>> be written out through filemap_fdatawrite or filemap_write_and_wait.
>>
>
> No. RHEL5 at that time didn't have a launder page method (it does now,
> but that's another story).
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
But what's about these two groups of calls? Are you agree with them?
--
Best regards,
Pavel Shilovsky.
--
To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
