linux-kernel - Re: init's children list is long and slows reaping children.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 10 Apr 2007 00:37:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Dave Jones <davej@...hat.com>, Robin Holt <holt@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jack Steiner <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

On Tue, 10 Apr 2007 03:05:56 -0400 Jeff Garzik <jeff@...zik.org> wrote:

> My main 
> worry with keventd is that we might get stuck behind an unrelated 
> process for an undefined length of time.

I don't think it has ever been demonstrated that keventd latency is
excessive, or a problem.  I guess we could instrument it and fix stuff
easily enough.

The main problem with keventd has been flush_scheduled_work() deadlocks: the
caller of flush_scheduled_work() wants to flush work item A, but holds some
lock which is also needed by unrelated work item B.  Most of the time, it
works.  But if item B happens to be queued the flush_scheduled_work() will
deadlock.

The fix is to flush-and-cancel just item A: if it's not running yet, cancel
it.  If it is running, wait until it has finished.  Oleg's

	void cancel_work_sync(struct work_struct *work)

is queued for 2.6.22 and should permit some kthread->keventd conversions
which would previously been deadlocky.

The thing to concentrate on here is the per-cpu threads, which is where the
proliferation appears to be coming from.  Conversions to
schedule_work()+cancel_work_sync() and conversions to
create_singlethread_workqueue().

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/