linux-kernel - Re: [BUG] signal: multithread program returns with wrong errno on receiving SIGSTOP

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Date:	Tue, 29 May 2007 00:33:54 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Satoru Takeuchi <takeuchi_satoru.jp@...itsu.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [BUG] signal: multithread program returns with wrong errno on receiving SIGSTOP

Your fix seems like the only way to go.  From skimming all the ERESTART*
uses, I think that in all cases (except for n_tty.c:job_control before your
patch), TIF_SIGPENDING is indeed set when a thread returns -ERESTART*.

But it makes me realize that there is a danger of leaking a -ERESTART*
return code to userland when TIF_SIGPENDING gets cleared by another thread
doing a recalc_sigpending_tsk.  Because of -ERESTART* I think we must make
it a rule that no thread can clear another thread's TIF_SIGPENDING, only
set it (unless it's known to be stopped in the signal code or something).
>From our recent work on it, I think that do_sigaction is in fact the only
place this can happen.  So that says we should err in the other direction
from what I said before in do_sigaction, and not have it do recalc at all.


Thanks,
Roland
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