linux-kernel - Re: [PATCH] ptrace: add ability to retrieve signals without removing from a queue (v2)

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Message-ID: <CANaxB-y_=267DABXjBdxjM=unt34mTnC8UQ64on7dHezta31gQ@mail.gmail.com>
Date:	Mon, 25 Feb 2013 14:46:36 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	linux-kernel@...r.kernel.org, criu@...nvz.org,
	linux-api@...r.kernel.org, Roland McGrath <roland@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pedro Alves <palves@...hat.com>
Subject: Re: [PATCH] ptrace: add ability to retrieve signals without removing
 from a queue (v2)

2013/2/25 Pavel Emelyanov <xemul@...allels.com>:
>> +     for (i = 0; i < arg.nr; i++) {
>> +             off = arg.off + i;
>> +
>> +             spin_lock_irq(&child->sighand->siglock);
>> +             list_for_each_entry(q, &pending->list, list) {
>> +                     if (!off--) {
>> +                             copy_siginfo(&info, &q->info);
>> +                             break;
>> +                     }
>> +             }
>> +             spin_unlock_irq(&child->sighand->siglock);
>
> What's the point of arg.nr if you for every single siginfo drop the lock
> and perform linear search anyway?

arg.nr may be useful, if we will decide to optimize this part in a
future. Currently the problem with complexity of finding a signal in a
queue is true not only for this code. It exists for delivering
real-time signals as well. Probably in a future this problem will be
fixed for both cases by the same way.

Thanks,
  Andrew
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