linux-kernel - Re: [PATCH 1/3] coredump: introduce dump

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Date:	Fri, 8 Mar 2013 12:54:31 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Horman <nhorman@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] coredump: introduce dump_interrupted()

On Fri, Mar 8, 2013 at 9:59 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> By discussion with Mandeep Singh Baines <msb@...omium.org>.
>
> Change dump_write(), dump_seek() and do_coredump() to check
> signal_pending() and abort if it is true.
>
> We add the new trivial helper, dump_interrupted(), to document that
> this probably needs more work and to simplify the potential freezer
> changes. Perhaps it will have more callers.
>
> Ideally it should do try_to_freeze() but then we need the unpleasant
> changes in dump_write() and wait_for_dump_helpers(). So far we simply
> accept the fact that the freezer can truncate a core-dump but at least
> you can reliably suspend.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Mandeep Singh Baines <msb@...omium.org>

dump_write aborts anyway in the pipe case. pipe_wait is interruptible
and should return -ERESTARTSYS if there is a signal pending.

But I guess there is no signal pending check in the disk write path.
So this allows you to bail out early and unblock suspend instead of
trying to write out all the vmas to a slow disk.

You may want to consider just checking dump_interrupted() at the very
top of the functions instead.

Regards,
Mandeep

> ---
>  fs/coredump.c |   20 +++++++++++++++++---
>  1 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 5503d94..66f65f0 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -418,6 +418,17 @@ static void coredump_finish(struct mm_struct *mm, bool core_dumped)
>         mm->core_state = NULL;
>  }
>
> +static bool dump_interrupted(void)
> +{
> +       /*
> +        * SIGKILL or freezing() interrupt the coredumping. Perhaps we
> +        * can do try_to_freeze() and check __fatal_signal_pending(),
> +        * but then we need to teach dump_write() to restart and clear
> +        * TIF_SIGPENDING.
> +        */
> +       return signal_pending(current);
> +}
> +
>  static void wait_for_dump_helpers(struct file *file)
>  {
>         struct pipe_inode_info *pipe;
> @@ -636,7 +647,7 @@ void do_coredump(siginfo_t *siginfo)
>         if (displaced)
>                 put_files_struct(displaced);
>
> -       core_dumped = binfmt->core_dump(&cprm);
> +       core_dumped = !dump_interrupted() && binfmt->core_dump(&cprm);
>
>         if (ispipe && core_pipe_limit)
>                 wait_for_dump_helpers(cprm.file);
> @@ -664,7 +675,9 @@ fail:
>   */
>  int dump_write(struct file *file, const void *addr, int nr)
>  {
> -       return access_ok(VERIFY_READ, addr, nr) && file->f_op->write(file, addr, nr, &file->f_pos) == nr;
> +       return !dump_interrupted() &&
> +               access_ok(VERIFY_READ, addr, nr) &&
> +               file->f_op->write(file, addr, nr, &file->f_pos) == nr;
>  }
>  EXPORT_SYMBOL(dump_write);
>
> @@ -673,7 +686,8 @@ int dump_seek(struct file *file, loff_t off)
>         int ret = 1;
>
>         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
> -               if (file->f_op->llseek(file, off, SEEK_CUR) < 0)
> +               if (dump_interrupted() ||
> +                   file->f_op->llseek(file, off, SEEK_CUR) < 0)
>                         return 0;
>         } else {
>                 char *buf = (char *)get_zeroed_page(GFP_KERNEL);
> --
> 1.5.5.1
>
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