linux-kernel - Re: [PATCH v2 5/7] signal: sigprocmask() should do retarget_shared

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Date:	Fri, 22 Apr 2011 13:46:16 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikita V. Youshchenko" <nyoushchenko@...sta.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] signal: sigprocmask() should do
 retarget_shared_pending()

On Mon, 18 Apr 2011 15:45:57 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> In short, almost every changing of current->blocked is wrong, or at least
> can lead to the unexpected results.
> 
> For example. Two threads T1 and T2, T1 sleeps in sigtimedwait/pause/etc.
> kill(tgid, SIG) can pick T2 for TIF_SIGPENDING. If T2 calls sigprocmask()
> and blocks SIG before it notices the pending signal, nobody else can handle
> this pending shared signal.
> 
> I am not sure this is bug, but at least this looks strange imho. T1 should
> not sleep forever, there is a signal which should wake it up.
> 
> This patch moves the code which actually changes ->blocked into the new
> helper, set_current_blocked() and changes this code to call
> retarget_shared_pending() as exit_signals() does. We should only care about
> the signals we just blocked, we use "newset & ~current->blocked" as a mask.
> 
> We do not check !sigisemptyset(newblocked), retarget_shared_pending() is
> cheap unless mask & shared_pending.
> 
> Note: for this particular case we could simply change sigprocmask() to
> return -EINTR if signal_pending(), but then we should change other callers
> and, more importantly, if we need this fix then set_current_blocked() will
> have more callers and some of them can't restart. See the next patch as a
> random example.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

This looks much simpler to me.

Reviewed-by: Matt Fleming <matt.fleming@...ux.intel.com>
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