Re: [PATCH 2/2] fs: update atime before I/O in generic_file_read_iter

[Jan Kara <jack@suse.cz>]

On Fri 30-09-16 10:46:34, Christoph Hellwig wrote:
> After the call to ->direct_IO the final reference to the file might have
> been dropped by aio_complete already, and the call to file_accessed might
> cause a use after free.
> 
> Instead update the access time before the I/O, similar to how we
> update the time stamps before writes.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

The patch looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

But frankly it looks like a nasty catch that iocb->ki_filp can go away
under you in the AIO case. Do I get it right that this means there must be
some other thread closing your fd while the read is running, right?

Also it seems that file_end_write(file) call in aio_run_iocb() is prone to
the same race?

Won't we be better off to just to do additional get_file() / fput() pair in
the AIO submission path so that whole AIO submission path is guaranteed to
have struct file available? I understand this is very performance sensitive
path but we'll be adding just two atomic ops...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR