From: ebiederm@xmission.com (Eric W. Biederman)
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com
Subject: Re: [PATCH] [0/11] SYSCTL: Use RCU to avoid races with string sysctls
Date: Sun, 20 Dec 2009 17:59:59 -0800 [thread overview]
Message-ID: <m1eimpm6hs.fsf@fess.ebiederm.org> (raw)
In-Reply-To: <20091221220.243954235@firstfloor.org> (Andi Kleen's message of "Mon\, 21 Dec 2009 02\:20\:21 +0100 \(CET\)")
Andi Kleen <andi@firstfloor.org> writes:
> With BKL-less sysctls most of the writable string sysctls are racy. There
> is no locking on the reader side, so a reader could see an inconsistent
> string or worse miss the terminating null and walk of beyond it.
The walk will only extend up to the maximum length of the string.
So the worst case really is inconsistent data.
This is an unfortunate corner case. This is not a regression as this
has been the way things have worked for years. So probably 2.6.34
material.
> This patch kit adds a new "rcu string" variant to avoid these
> problems and convers the racy users. One the writer side the strings are
> always copied to new memory and the readers use rcu_read_lock()
> to get a stable view. For readers who access the string over
> sleeps the reader copies the string.
I will have to look more after the holidays. This rcu_string looks like
it introduces allocations on paths that did not use them before, which
has me wondering a bit.
Eric
next prev parent reply other threads:[~2009-12-21 2:00 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-21 1:20 [PATCH] [0/11] SYSCTL: Use RCU to avoid races with string sysctls Andi Kleen
2009-12-21 1:20 ` [PATCH] [1/11] Add rcustring ADT for RCU protected strings Andi Kleen
2009-12-22 2:46 ` Paul E. McKenney
2009-12-22 10:05 ` Andi Kleen
2009-12-22 20:59 ` Paul E. McKenney
2009-12-21 1:20 ` [PATCH] [2/11] Add a kernel_address() that works for data too Andi Kleen
2009-12-21 1:20 ` [PATCH] [3/11] SYSCTL: Add proc_rcu_string to manage sysctls using rcu strings Andi Kleen
2009-12-22 2:51 ` Paul E. McKenney
2009-12-22 3:00 ` Eric W. Biederman
2009-12-22 7:44 ` Paul E. McKenney
2009-12-21 1:20 ` [PATCH] [4/11] SYSCTL: Use RCU strings for core_pattern sysctl Andi Kleen
2009-12-21 1:20 ` [PATCH] [5/11] SYSCTL: Add call_usermodehelper_cleanup() Andi Kleen
2009-12-21 1:20 ` [PATCH] [6/11] SYSCTL: Convert modprobe_path to proc_rcu_string() Andi Kleen
2009-12-21 1:20 ` [PATCH] [7/11] SYSCTL: Convert poweroff_command to proc_rcu_string Andi Kleen
2009-12-21 1:20 ` [PATCH] [8/11] SYSCTL: Convert hotplug helper string to proc_rcu_string() Andi Kleen
2009-12-22 19:03 ` Greg KH
2009-12-21 1:20 ` [PATCH] [9/11] SYSCTL: Add a mutex to the page_alloc zone order sysctl Andi Kleen
2009-12-21 1:20 ` [PATCH] [10/11] SYSCTL: Use RCU protected sysctl for ocfs group add helper Andi Kleen
2009-12-21 1:20 ` [PATCH] [11/11] SYSCTL: Convert IRDA text sysctl to RCU Andi Kleen
2009-12-21 1:59 ` Eric W. Biederman [this message]
2009-12-21 2:04 ` [PATCH] [0/11] SYSCTL: Use RCU to avoid races with string sysctls Andi Kleen
2009-12-21 2:31 ` Eric W. Biederman
2009-12-21 3:21 ` Andi Kleen
-- strict thread matches above, loose matches on Subject: below --
2009-12-21 7:57 Alexey Dobriyan
2009-12-21 10:50 ` Andi Kleen
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