Re: [PATCH] exec: log when wait_for_dump_helpers aborts due to asignal

From: Oleg Nesterov
Date: Wed Oct 26 2011 - 13:38:55 EST

On 10/25, Mandeep Singh Baines wrote:
> To allow coredump pipe readers to look at /proc/<pid> of the crashing
> process, the kernel waits for the reader to exit. However, the wait
> is silently aborted if the crashing process is signalled.

Well, yes... But note that this signal_pending() is only used because
with TIF_SIGPENDING we have the problems anyway.

Oh. I promise myself I'll make do_coredump() killable and cleanup this
all every time I look at this code...

> This patch, logs whenever wait_for_dump_helpers is aborted or in order
> to assist in debugging cases where /proc/<pid> is gone.

I don't really understand why this is useful. The reader process
can complain if it can't collect the data (say, /proc/pid goes away
or EOF doesn't come).

As for the patch itself,

> - while ((pipe->readers > 1) && (!signal_pending(current))) {
> + while (pipe->readers > 1) {
> + if (signal_pending(current)) {
> + pr_info("wait_for_dump_helpers[%d]: "
> + "aborted due to signal\n",
> + task_pid_nr(current));
> + break;
> + }
> +
> wake_up_interruptible_sync(&pipe->wait);

This can't help in general. If signal_pending() == T, it is quite
possible that pipe_write() already failed before.


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