From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Michel Lespinasse <walken@google.com>
Cc: kosaki.motohiro@jp.fujitsu.com,
Linus Torvalds <torvalds@linux-foundation.org>,
David Howells <dhowells@redhat.com>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Waychison <mikew@google.com>,
Suleiman Souhlal <suleiman@google.com>,
Ying Han <yinghan@google.com>
Subject: Re: [PATCH 12/12] Use down_read_unfair() for /sys/<pid>/exe and /sys/<pid>/maps files
Date: Thu, 13 May 2010 09:32:32 +0900 (JST) [thread overview]
Message-ID: <20100513091659.214D.A69D9226@jp.fujitsu.com> (raw)
In-Reply-To: <n2z8d20b11a1005121635qaa544981v620374f43c15945d@mail.gmail.com>
> > Is it good idea?
> > So I think /proc shouldn't use unfair thing as backdoor.
> > It doesn't only makes performance improvement, but also
> > DoS chance is there.
>
> I am not entirely surprised that there is some level of opposition to
> this change (which is in part why it went last in the series).
>
> Besides keeping it internal, would there be ways to make it acceptable
> to the community ? For example, would it be fine if unfair behavior
> was only used if the caller thread runs with root priviledge ?
Umm. seems no good idea.
Why?
In nowadays, root priviledge should be considered to blocked by security module.
but this using way can't combinate with any security module. at least we need
more proper and security friendly interface.
> In my opinion the optimal behavior would be if the rwsem could be
> allowed to be grabbed unfairly only as long as there are still fair
> readers on it. However, I don't see how to achieve this given that we
> don't want to slow down the regular, fair code paths.
dumb question.
Why do you need to read /proc/<pid>/exec and /proc/<pid>/maps?
To make new /proc files makes help?
IOW, do we really need unfair reader? can't we make more fine grained lock?
next prev parent reply other threads:[~2010-05-13 0:32 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-12 3:20 [PATCH 00/12] rwsem changes + down_read_unfair() proposal Michel Lespinasse
2010-05-12 3:20 ` [PATCH 01/12] rwsem: test for no active locks in __rwsem_do_wake undo code Michel Lespinasse
2010-05-12 3:20 ` [PATCH 02/12] rwsem: use single atomic update for sem count when waking up readers Michel Lespinasse
2010-05-12 3:20 ` [PATCH 03/12] rwsem: let RWSEM_WAITING_BIAS represent any number of waiting threads Michel Lespinasse
2010-05-12 3:20 ` [PATCH 04/12] rwsem: consistently use adjustment variable Michel Lespinasse
2010-05-12 3:20 ` [PATCH 05/12] x86 rwsem: take advantage of new RWSEM_WAITING_BIAS semantics Michel Lespinasse
2010-05-12 3:20 ` [PATCH 06/12] rwsem: wake queued readers when other readers are active Michel Lespinasse
2010-05-12 3:20 ` [PATCH 07/12] rwsem: wake queued readers when writer blocks on active read lock Michel Lespinasse
2010-05-12 3:20 ` [PATCH 08/12] rwsem: smaller wrappers around rwsem_down_failed_common Michel Lespinasse
2010-05-12 3:20 ` [PATCH 09/12] generic rwsem: implement down_read_unfair Michel Lespinasse
2010-05-12 3:21 ` [PATCH 10/12] rwsem: down_read_unfair infrastructure support Michel Lespinasse
2010-05-12 3:21 ` [PATCH 11/12] x86 rwsem: down_read_unfair implementation Michel Lespinasse
2010-05-12 3:21 ` [PATCH 12/12] Use down_read_unfair() for /sys/<pid>/exe and /sys/<pid>/maps files Michel Lespinasse
2010-05-12 22:53 ` KOSAKI Motohiro
2010-05-12 23:35 ` Michel Lespinasse
2010-05-13 0:32 ` KOSAKI Motohiro [this message]
2010-05-12 10:39 ` [PATCH 01/12] rwsem: test for no active locks in __rwsem_do_wake undo code David Howells
2010-05-12 11:01 ` [PATCH 02/12] rwsem: use single atomic update for sem count when waking up readers David Howells
2010-05-13 0:54 ` Michel Lespinasse
2010-05-12 11:36 ` David Howells
2010-05-12 11:45 ` [PATCH 04/12] rwsem: consistently use adjustment variable David Howells
2010-05-13 1:12 ` Michel Lespinasse
2010-05-12 12:10 ` [PATCH 05/12] x86 rwsem: take advantage of new RWSEM_WAITING_BIAS semantics David Howells
2010-05-12 12:22 ` [PATCH 06/12] rwsem: wake queued readers when other readers are active David Howells
2010-05-13 2:39 ` Michel Lespinasse
2010-05-13 5:41 ` Michel Lespinasse
2010-05-12 12:33 ` [PATCH 07/12] rwsem: wake queued readers when writer blocks on active read lock David Howells
2010-05-12 12:36 ` [PATCH 08/12] rwsem: smaller wrappers around rwsem_down_failed_common David Howells
2010-05-12 12:42 ` David Howells
2010-05-13 2:54 ` Michel Lespinasse
2010-05-12 12:46 ` [PATCH 09/12] generic rwsem: implement down_read_unfair David Howells
2010-05-12 13:08 ` [PATCH 11/12] x86 rwsem: down_read_unfair implementation David Howells
2010-05-12 13:10 ` [PATCH 12/12] Use down_read_unfair() for /sys/<pid>/exe and /sys/<pid>/maps files David Howells
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