On Mon, 14 Nov 2011 17:15:24 +0100
Jan Kara <jack@xxxxxxx> wrote:
> Currently write(2) to a file is not interruptible by a signal. Sometimes this
> is desirable (e.g. when you want to quickly kill a process hogging your disk or
> when some process gets blocked in balance_dirty_pages() indefinitely due to a
> filesystem being in an error condition).
>
> Reported-by: Kazuya Mio <k-mio@xxxxxxxxxxxxx>
> Tested-by: Kazuya Mio <k-mio@xxxxxxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> mm/filemap.c | 11 +++++++++--
> 1 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index c0018f2..166b30e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2407,7 +2407,6 @@ static ssize_t generic_perform_write(struct file *file,
> iov_iter_count(i));
>
> again:
> -
> /*
> * Bring in the user page that we will copy from _first_.
> * Otherwise there's a nasty deadlock on copying from the
> @@ -2463,7 +2462,15 @@ again:
> written += copied;
>
> balance_dirty_pages_ratelimited(mapping);
> -
> + /*
> + * We check the signal independently of balance_dirty_pages()
> + * because we need not wait and check for signal there although
> + * this loop could have taken significant amount of time...
> + */
> + if (fatal_signal_pending(current)) {
> + status = -EINTR;
> + break;
> + }
> } while (iov_iter_count(i));
>
> return written ? written : status;
Will this permit the interruption of things like fsync() or sync()? If
so, considerable pondering is needed.
Also I worry about stuff like the use of buffered write to finish off
loose ends in direct-IO writing. Sometimes these writes MUST complete,
to prevent exposing unwritten disk blocks to a subsequent read. Will a
well-timed ^C break this? If "no" then does this change introduce risk
that we'll later accidentally introduce such a security hole?
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