Re: [PATCH 3/3] exec: Allow do_coredump to wait for user space pipe readers to complete (v5)

Oleg Nesterov
2009-07-01T16:10:18Z

Neil, the changelog is not right,

On 07/01, Neil Horman wrote:
>
> We basically add ourselves as an additional
> reader (to prevent cleanup of the pipe), write the dump in ->core_dump(),

This is not what we do. We do not and must not inc readers before
->core_dump(). We only do this in wait_for_dump_helpers().

> note that we add ourselves as a reader before writing the
> file. this closes the race in the window between the time we write the dump and
> the time we start checking for the user space process to be done with the pipe.

again, this doesn't match the patch.

> +static void wait_for_dump_helpers(struct file *file)
> +{
> + struct pipe_inode_info *pipe;
> +
> + pipe = file->f_path.dentry->d_inode->i_pipe;
> +
> + pipe_lock(pipe);
> + pipe->readers++;
> + pipe->writers--;
> + while (pipe->readers > 1) {
> + wake_up_interruptible_sync(&pipe->wait);
> + kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
> + pipe_wait(pipe);
> + }
> +
> + /*
> + * This reclaims the additional readers count we took in
> + * do_coredump
> + */

now the comment is wrong.

Can't understand why do you change readers/writers unconditianally,
we shouldn't have the false wakeups since ->writers == 0, but OK.

Oleg.