Re: Patch "fs: move kiocb_start_write() into vfs_iocb_iter_write()" has been added to the 6.6-stable tree

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On Thu, May 30, 2024 at 10:05 PM Sasha Levin <sashal@xxxxxxxxxx> wrote:
>
> This is a note to let you know that I've just added the patch titled
>
>     fs: move kiocb_start_write() into vfs_iocb_iter_write()
>
> to the 6.6-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
>      fs-move-kiocb_start_write-into-vfs_iocb_iter_write.patch
> and it can be found in the queue-6.6 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@xxxxxxxxxxxxxxx> know about it.
>
>
>
> commit 17f38d69e7960a2b346db04750b0e4ba867c0b83
> Author: Amir Goldstein <amir73il@xxxxxxxxx>
> Date:   Wed Nov 22 14:27:12 2023 +0200
>
>     fs: move kiocb_start_write() into vfs_iocb_iter_write()
>
>     [ Upstream commit 6ae654392bb516a0baa47fed1f085d84e8cad739 ]
>
>     In vfs code, sb_start_write() is usually called after the permission hook
>     in rw_verify_area().  vfs_iocb_iter_write() is an exception to this rule,
>     where kiocb_start_write() is called by its callers.
>
>     Move kiocb_start_write() from the callers into vfs_iocb_iter_write()
>     after the rw_verify_area() checks, to make them "start-write-safe".
>
>     The semantics of vfs_iocb_iter_write() is changed, so that the caller is
>     responsible for calling kiocb_end_write() on completion only if async
>     iocb was queued.  The completion handlers of both callers were adapted
>     to this semantic change.
>

This comment about semantics change looks like a clue from my past
self that backporting this commit as standalone is risky.

This commit was part of a pretty big shuffle in splice and ovl code.
I'd feel much more comfortable with backporting the entire ovl
series 14ab6d425e8067..5b02bfc1e7e3 and splice series
v6.7..6ae654392bb51 than just 3 individual commits in the middle.

Thanks,
Amir.




>     This is needed for fanotify "pre content" events.
>
>     Suggested-by: Jan Kara <jack@xxxxxxx>
>     Suggested-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
>     Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
>     Link: https://lore.kernel.org/r/20231122122715.2561213-14-amir73il@xxxxxxxxx
>     Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
>     Reviewed-by: Jan Kara <jack@xxxxxxx>
>     Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
>     Stable-dep-of: 7c98f7cb8fda ("remove call_{read,write}_iter() functions")
>     Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
> index 009d23cd435b5..5857241c59181 100644
> --- a/fs/cachefiles/io.c
> +++ b/fs/cachefiles/io.c
> @@ -259,7 +259,8 @@ static void cachefiles_write_complete(struct kiocb *iocb, long ret)
>
>         _enter("%ld", ret);
>
> -       kiocb_end_write(iocb);
> +       if (ki->was_async)
> +               kiocb_end_write(iocb);
>
>         if (ret < 0)
>                 trace_cachefiles_io_error(object, inode, ret,
> @@ -319,8 +320,6 @@ int __cachefiles_write(struct cachefiles_object *object,
>                 ki->iocb.ki_complete = cachefiles_write_complete;
>         atomic_long_add(ki->b_writing, &cache->b_writing);
>
> -       kiocb_start_write(&ki->iocb);
> -
>         get_file(ki->iocb.ki_filp);
>         cachefiles_grab_object(object, cachefiles_obj_get_ioreq);
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 9fd88579bfbfb..a1c64c2b8e204 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -295,10 +295,8 @@ static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
>         struct kiocb *iocb = &aio_req->iocb;
>         struct kiocb *orig_iocb = aio_req->orig_iocb;
>
> -       if (iocb->ki_flags & IOCB_WRITE) {
> -               kiocb_end_write(iocb);
> +       if (iocb->ki_flags & IOCB_WRITE)
>                 ovl_file_modified(orig_iocb->ki_filp);
> -       }
>
>         orig_iocb->ki_pos = iocb->ki_pos;
>         ovl_aio_put(aio_req);
> @@ -310,6 +308,9 @@ static void ovl_aio_rw_complete(struct kiocb *iocb, long res)
>                                                    struct ovl_aio_req, iocb);
>         struct kiocb *orig_iocb = aio_req->orig_iocb;
>
> +       if (iocb->ki_flags & IOCB_WRITE)
> +               kiocb_end_write(iocb);
> +
>         ovl_aio_cleanup_handler(aio_req);
>         orig_iocb->ki_complete(orig_iocb, res);
>  }
> @@ -421,7 +422,6 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
>                 aio_req->iocb.ki_flags = ifl;
>                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
>                 refcount_set(&aio_req->ref, 2);
> -               kiocb_start_write(&aio_req->iocb);
>                 ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
>                 ovl_aio_put(aio_req);
>                 if (ret != -EIOCBQUEUED)
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 4771701c896ba..9a56949f3b8d1 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -865,6 +865,10 @@ static ssize_t do_iter_write(struct file *file, struct iov_iter *iter,
>         return ret;
>  }
>
> +/*
> + * Caller is responsible for calling kiocb_end_write() on completion
> + * if async iocb was queued.
> + */
>  ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
>                             struct iov_iter *iter)
>  {
> @@ -885,7 +889,10 @@ ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
>         if (ret < 0)
>                 return ret;
>
> +       kiocb_start_write(iocb);
>         ret = call_write_iter(file, iocb, iter);
> +       if (ret != -EIOCBQUEUED)
> +               kiocb_end_write(iocb);
>         if (ret > 0)
>                 fsnotify_modify(file);
>





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