On Wed, Oct 11, 2017 at 11:19 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Wed, Oct 11, 2017 at 11:02:56AM -0400, Olga Kornievskaia wrote:
>> On Wed, Oct 11, 2017 at 10:07 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>> > On Tue, Oct 10, 2017 at 05:14:29PM -0400, Olga Kornievskaia wrote:
>> >> On Mon, Oct 9, 2017 at 11:58 AM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
>> >> > On Mon, Oct 09, 2017 at 10:53:13AM -0400, Olga Kornievskaia wrote:
>> >> >> On Thu, Sep 28, 2017 at 2:38 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
>> >> >> > On Thu, Sep 28, 2017 at 01:29:43PM -0400, Olga Kornievskaia wrote:
>> >> >> >> Upon receiving OFFLOAD_CANCEL search the list of copy stateids,
>> >> >> >> if found mark it cancelled. If copy has more interations to
>> >> >> >> call vfs_copy_file_range, it'll stop it. Server won't be sending
>> >> >> >> CB_OFFLOAD to the client since it received a cancel.
>> >> >> >>
>> >> >> >> Signed-off-by: Olga Kornievskaia <kolga@xxxxxxxxxx>
>> >> >> >> ---
>> >> >> >> fs/nfsd/nfs4proc.c | 26 ++++++++++++++++++++++++--
>> >> >> >> fs/nfsd/nfs4state.c | 16 ++++++++++++++++
>> >> >> >> fs/nfsd/state.h | 4 ++++
>> >> >> >> 3 files changed, 44 insertions(+), 2 deletions(-)
>> >> >> >>
>> >> >> >> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
>> >> >> >> index 3cddebb..f4f3d93 100644
>> >> >> >> --- a/fs/nfsd/nfs4proc.c
>> >> >> >> +++ b/fs/nfsd/nfs4proc.c
>> >> >> >> @@ -1139,6 +1139,7 @@ static int _nfsd_copy_file_range(struct nfsd4_copy *copy)
>> >> >> >> size_t bytes_to_copy;
>> >> >> >> u64 src_pos = copy->cp_src_pos;
>> >> >> >> u64 dst_pos = copy->cp_dst_pos;
>> >> >> >> + bool cancelled = false;
>> >> >> >>
>> >> >> >> do {
>> >> >> >> bytes_to_copy = min_t(u64, bytes_total, MAX_RW_COUNT);
>> >> >> >> @@ -1150,7 +1151,12 @@ static int _nfsd_copy_file_range(struct nfsd4_copy *copy)
>> >> >> >> copy->cp_res.wr_bytes_written += bytes_copied;
>> >> >> >> src_pos += bytes_copied;
>> >> >> >> dst_pos += bytes_copied;
>> >> >> >> - } while (bytes_total > 0 && !copy->cp_synchronous);
>> >> >> >> + if (!copy->cp_synchronous) {
>> >> >> >> + spin_lock(©->cps->cp_lock);
>> >> >> >> + cancelled = copy->cps->cp_cancelled;
>> >> >> >> + spin_unlock(©->cps->cp_lock);
>> >> >> >> + }
>> >> >> >> + } while (bytes_total > 0 && !copy->cp_synchronous && !cancelled);
>> >> >> >> return bytes_copied;
>> >> >> >
>> >> >> > I'd rather we sent a signal, and then we won't need this
>> >> >> > logic--vfs_copy_range() will just return EINTR or something.
>> >> >>
>> >> >> Hi Bruce,
>> >> >>
>> >> >> Now that I've implemented using the kthread instead of the workqueue,
>> >> >> I don't see that it can provide any better guarantee than the work
>> >> >> queue. vfs_copy_range() is not interrupted in the middle and returning
>> >> >> the EINTR. The function that runs the kthread, it has to at some point
>> >> >> call signalled()/kthread_should_stop() function to see if it was
>> >> >> signaled and use it to 'stop working instead of continuing on'.
>> >> >>
>> >> >> If I were to remove the loop and check (if signaled() ||
>> >> >> kthread_should_stop()) before and after calling the
>> >> >> vfs_copy_file_range(), the copy will either not start if the
>> >> >> OFFLOAD_CANCEL was received before copy started or the whole copy
>> >> >> would happen.
>> >> >>
>> >> >> Even with the loop, I'd be checking after every call for
>> >> >> vfs_copy_file_range() just like it was in the current version with the
>> >> >> workqueue.
>> >> >>
>> >> >> Please advise if you still want the kthread-based implementation or
>> >> >> keep the workqueue.
>> >> >
>> >> > That's interesting.
>> >> >
>> >> > To me that sounds like a bug somewhere under vfs_copy_file_range().
>> >> > splice_direct_to_actor() can do long-running copies, so it should be
>> >> > interruptible, shouldn't it?
>> >>
>> >> So I found it. Yes do_splice_direct() will react to somebody sending a
>> >> ctrl-c and will stop. It calls signal_pendning(). However, in our
>> >> case, I'm calling kthread_stop() and that sets a different flag and
>> >> one needs to also check for kthread_should_stop() as a stopping
>> >> condition. splice.c lacks that.
>> >>
>> >> I hope they can agree that it's a bug. I don't have any luck with VFS...
>> >
>> > Argh. No, it's probably not their bug, I guess kthreads just ignore
>> > signals. OK, I can't immediately see what the right thing to do is
>> > here....
>> >
>> > I do think we need to do something as we want to be able to interrupt
>> > and clean up copy threads when we can.
>>
>> A bug is not the right word. It would be asking them to accommodate
>> stopping to include kthread_stop condition. Why do you say kthreads
>> ignore signals? You can say that kthread_stop doesn't send a signal.
>
> I think both are true.
>
> I doubt it's reasonable to add kthread_should_stop everywhere that
> there are currently checks for signals.
>
>> Also another note, I still can't remove the loop around the call to
>> the vfs_copy_file_range() because it's not guaranteed to copy all the
>> bytes that the call asks for. The implementation of
>> vfs_copy_file_range will do_splice_direct only MAX_RW_COUNT at a time.
>> So the upper layer needs to loop to make sure it copies all the bytes.
>
> MAX_RW_COUNT is about 4 gigs. I'm not sure if it's really a problem to
> copy only 4 gigs at a time? But, yes, maybe the loop is still worth it.
>
>> If VFS will decide to reject the request to add kthread_should_stop to
>> their conditions, then the loop could be a way to stop every 4MB.
>> Copying 4MB would be the equivalent of what the current synchronous
>> copy does now anyway?
>
> I'm still a little worried about copy threads hanging indefinitely if
> the peer goes away mid-copy. The ability to signal the copy thread
> would help.
So I don't know if this is ok or not but I can directly set the
SIGPENDING bit in the copy task structure from the OFFLOAD_CANCEL
thread and that stops the splice copy too.
>
> --b.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
