linux-kernel - Re: [RFC][PATCH 0/5] Optimize percpu-rwsem

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]

Message-ID: <20150605014558.GS7232@ZenIV.linux.org.uk>
Date:	Fri, 5 Jun 2015 02:45:58 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Davidlohr Bueso <dave@...olabs.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	der.herr@...r.at
Subject: Re: [RFC][PATCH 0/5] Optimize percpu-rwsem

On Tue, May 26, 2015 at 02:57:53PM -0700, Linus Torvalds wrote:

> Because that is another example of a complete failure of a locking
> primitive that was just too specialized to be worth it.

<notices stale include in fs/file_table.c and removes it>

FWIW, I hadn't really looked into stop_machine uses, but fs/locks.c one
is really not all that great - there we have a large trashcan of a list
(every file_lock on the system) and the only use of that list is /proc/locks
output generation.  Sure, additions take this CPU's spinlock.  And removals
take pretty much a random one - losing the timeslice and regaining it on
a different CPU is quite likely with the uses there.

Why do we need a global lock there, anyway?  Why not hold only one for
the chain currently being traversed?  Sure, we'll need to get and drop
them in ->next() that way; so what?
--
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/