linux-kernel - Re: [PATCH] coredump: Retry writes where appropriate

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Date:	Tue, 2 Jun 2009 02:08:50 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, paul@...-scientist.net,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] coredump: Retry writes where appropriate

On 06/01, Roland McGrath wrote:
>
> That is almost a separate subject, really.  Having i/o calls' waits wrongly
> interrupted and then clearing TIF_SIGPENDING just seems goofy to me.

Yes, agreed. The patch I sent make the coredumping task invisible to all
signals except SIGKILL.

> But there is the possibility of recalc_sigpending_and_wake
> via cancel_freezing, at least.  Seems safer to make recalc_sigpending_tsk
> robust in this case.

Oh, I forgot about freezer...

Well, not good to complicate recalc_sigpending_tsk() for this unlikely case.
And this can't help, freezer does signal_wake_up() unconditionally.

So in fact this is another argument to check signal_pending() and clear it
in dump_write/seek.

But since the coredumping task is not freezable anyway, perhaps we should
change fake_signal_wake_up() to ignore SIGNAL_GROUP_DUMPING task.

Or we should make the coredumping freezable. This means dump_write/seek
and exit_mm() should do try_to_freeze().

In any case, the coredumping is special. If ->write() returns -ERESTART/EINTR
it assumes the return to ths user-space, this is not true for the coredump.
This means that handling the spurious signals in coredump_file_write() is
not so bad if we can't avoid this.

Oleg.

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