Re: [PATCH] fs/netfs/fscache_io: remove the obsolete "using_pgpriv2" flag

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2024-07-29 at 17:35 +0200, Max Kellermann wrote:
> On Mon, Jul 29, 2024 at 2:56 PM Jeff Layton <jlayton@kernel.org>
> wrote:
> > Either way, you can add this to both patches:
> > 
> > Reviewed-by: Jeff Layton <jlayton@kernel.org>
> 
> Stop the merge :-)
> 
> I just found that my patch introduces another lockup; copy_file_range
> locks up this way:
> 
>  [<0>] folio_wait_private_2+0xd9/0x140
>  [<0>] ceph_write_begin+0x56/0x90
>  [<0>] generic_perform_write+0xc0/0x210
>  [<0>] ceph_write_iter+0x4e2/0x650
>  [<0>] iter_file_splice_write+0x30d/0x550
>  [<0>] splice_file_range_actor+0x2c/0x40
>  [<0>] splice_direct_to_actor+0xee/0x270
>  [<0>] splice_file_range+0x80/0xc0
>  [<0>] ceph_copy_file_range+0xbb/0x5b0
>  [<0>] vfs_copy_file_range+0x33e/0x5d0
>  [<0>] __x64_sys_copy_file_range+0xf7/0x200
>  [<0>] do_syscall_64+0x64/0x100
>  [<0>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
> Turns out that there are still private_2 users left in both fs/ceph
> and fs/netfs. My patches fix one problem, but cause another problem.
> Too bad!
> 
> This leaves me confused again: how shall I fix this? Can all
> folio_wait_private_2() calls simply be removed?
> This looks like some refactoring gone wrong, and some parts don't
> make
> sense (like netfs and ceph claim ownership of the folio_private
> pointer). I could try to fix the mess, but I need to know how this is
> meant to be. David, can you enlighten me?
> 
> Max

I suspect the folio_wait_private_2 call in ceph_write_begin should have
also been removed in ae678317b95, and it just got missed somehow in the
original patch. All of the other callsites that did anything with
private_2 were removed in that patch.

David, can you confirm that?
-- 
Jeff Layton <jlayton@kernel.org>