From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Jones <davej@redhat.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
rostedt <rostedt@goodmis.org>, dhowells <dhowells@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: lockdep trace from posix timers
Date: Mon, 20 Aug 2012 17:56:51 +0200 [thread overview]
Message-ID: <1345478211.23018.69.camel@twins> (raw)
In-Reply-To: <20120820154154.GB20258@redhat.com>
On Mon, 2012-08-20 at 17:41 +0200, Oleg Nesterov wrote:
> I won't insist. The patch I sent uses PF_EXITING and the fake
> "struct callback_head* TWORK_EXITED", but this looks almost the same.
Right, I used a fake callback_head because it avoided a few special
cases since its a dereferencable pointer.
> > > Note also your patch breaks fifo, but this is fixable.
> >
> > Why do you care about the order?
>
> IMHO, this is just more natural.
Depends on what you're used to I guess ;-) Both RCU and irq_work are
filo, this seems to be the natural way for single linked lists.
> For example. keyctl_session_to_parent() does _cancel only to protect
> from exploits doing keyctl(KEYCTL_SESSION_TO_PARENT) in an endless
> loop. It could simply do task_work_add(), but in this case we need
> fifo for correctness.
I'm not entirely sure I see, not doing the cancel would delay the free
until the executing of key_change_session_keyring()? doing that keyctl()
in an indefinite loop involves going back to userspace, so where's the
resource issue?
Also, I'm not seeing where the FIFO requirement comes from.
> > Iterating a single linked queue in fifo
> > seems more expensive than useful.
>
> Currently the list is fifo (we add to the last element), this is O(1).
depends on what way you look at the list I guess, with a single linked
list there's only one end you can add to in O(1), so we're calling that
the tail?
> But the list should be short, we can reverse it in _run() if we change
> task_work_add() to add to the head.
Reversing a (single linked) list is O(n^2).. which is indeed doable for
short lists, but why assume its short?
next prev parent reply other threads:[~2012-08-20 15:57 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-24 20:36 lockdep trace from posix timers Dave Jones
2012-07-27 16:20 ` Dave Jones
2012-08-16 12:54 ` Ming Lei
2012-08-16 14:03 ` Dave Jones
2012-08-16 18:07 ` Peter Zijlstra
2012-08-17 15:14 ` Oleg Nesterov
2012-08-17 15:17 ` Oleg Nesterov
2012-08-17 16:40 ` task_work_add() should not succeed unconditionally (Was: lockdep trace from posix timers) Oleg Nesterov
2012-08-20 7:15 ` lockdep trace from posix timers Peter Zijlstra
2012-08-20 11:44 ` Peter Zijlstra
2012-08-20 11:46 ` Peter Zijlstra
2012-08-20 11:50 ` Peter Zijlstra
2012-08-20 12:19 ` Steven Rostedt
2012-08-20 12:20 ` Peter Zijlstra
2012-08-20 14:59 ` Oleg Nesterov
2012-08-20 15:10 ` Peter Zijlstra
2012-08-20 15:27 ` Peter Zijlstra
2012-08-20 15:32 ` Oleg Nesterov
2012-08-20 15:46 ` Peter Zijlstra
2012-08-20 15:58 ` Oleg Nesterov
2012-08-20 16:03 ` Peter Zijlstra
2012-08-20 15:05 ` Oleg Nesterov
2012-08-20 15:12 ` Peter Zijlstra
2012-08-20 15:41 ` Oleg Nesterov
2012-08-20 15:56 ` Peter Zijlstra [this message]
2012-08-20 16:10 ` Oleg Nesterov
2012-08-20 16:19 ` Peter Zijlstra
2012-08-20 16:23 ` Oleg Nesterov
2012-08-21 18:27 ` Oleg Nesterov
2012-08-21 18:34 ` Oleg Nesterov
2012-08-24 18:56 ` Oleg Nesterov
2012-08-26 19:11 ` [PATCH 0/4] (Was: lockdep trace from posix timers) Oleg Nesterov
2012-08-26 19:12 ` [PATCH 1/4] task_work: make task_work_add() lockless Oleg Nesterov
2012-09-14 6:08 ` [tip:core/urgent] task_work: Make " tip-bot for Oleg Nesterov
2012-09-24 19:27 ` [PATCH 1/4] task_work: make " Geert Uytterhoeven
2012-09-24 20:37 ` Oleg Nesterov
2012-08-26 19:12 ` [PATCH 2/4] task_work: task_work_add() should not succeed after exit_task_work() Oleg Nesterov
2012-09-14 6:09 ` [tip:core/urgent] " tip-bot for Oleg Nesterov
2012-08-26 19:12 ` [PATCH 3/4] task_work: revert d35abdb2 "hold task_lock around checks in keyctl" Oleg Nesterov
2012-09-14 6:10 ` [tip:core/urgent] task_work: Revert " hold " tip-bot for Oleg Nesterov
2012-08-26 19:12 ` [PATCH 4/4] task_work: simplify the usage in ptrace_notify() and get_signal_to_deliver() Oleg Nesterov
2012-09-14 6:11 ` [tip:core/urgent] task_work: Simplify " tip-bot for Oleg Nesterov
2012-09-06 18:01 ` [PATCH 0/4] (Was: lockdep trace from posix timers) Oleg Nesterov
2012-09-06 18:35 ` Peter Zijlstra
2012-09-07 13:13 ` Oleg Nesterov
2012-08-28 16:29 ` lockdep trace from posix timers Peter Zijlstra
2012-08-28 17:01 ` Oleg Nesterov
2012-08-28 17:12 ` Oleg Nesterov
2012-08-28 17:28 ` Peter Zijlstra
2012-08-29 15:25 ` Oleg Nesterov
2012-08-20 14:55 ` Oleg Nesterov
2012-08-20 15:43 ` Oleg Nesterov
2012-08-20 15:48 ` Peter Zijlstra
2012-08-20 15:58 ` Oleg Nesterov
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