From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-tip-commits@vger.kernel.org, dave@stgolabs.net,
hpa@zytor.com, sasha.levin@oracle.com, tglx@linutronix.de,
linux-kernel@vger.kernel.org, jason.low2@hp.com,
walken@google.com, akpm@linux-foundation.org, mingo@kernel.org,
paulmck@linux.vnet.ibm.com, davej@codemonkey.org.uk,
ming.lei@canonical.com, peterz@infradead.org,
torvalds@linux-foundation.org, tim.c.chen@linux.intel.com
Subject: Re: [tip:locking/core] locking/rwsem: Fix lock optimistic spinning when owner is not running
Date: Sat, 7 Mar 2015 18:13:47 +0100 [thread overview]
Message-ID: <20150307171347.GA30365@redhat.com> (raw)
In-Reply-To: <tip-9198f6edfd9ced74fd90b238d5a354aeac89bdfa@git.kernel.org>
I think the patch is fine, but this reminds me...
On 03/07, tip-bot for Jason Low wrote:
>
> bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
> {
> long count;
>
> rcu_read_lock();
> - while (owner_running(sem, owner)) {
> - /* abort spinning when need_resched */
> - if (need_resched()) {
> + while (sem->owner == owner) {
> + /*
> + * Ensure we emit the owner->on_cpu, dereference _after_
> + * checking sem->owner still matches owner, if that fails,
> + * owner might point to free()d memory, if it still matches,
> + * the rcu_read_lock() ensures the memory stays valid.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Yes, this is another case when we wrongly assume this.
Peter, should I resend
[PATCH 3/3] introduce task_rcu_dereference()
http://marc.info/?l=linux-kernel&m=141443631413914
? or should we add another call_rcu() in finish_task_switch() (like -rt does)
to make this true?
Oleg.
next prev parent reply other threads:[~2015-03-07 17:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-07 7:45 [PATCH] locking/rwsem: Fix lock optimistic spinning when owner is not running Jason Low
2015-03-07 9:21 ` Peter Zijlstra
2015-03-09 17:42 ` Jason Low
2015-03-07 16:43 ` [tip:locking/core] " tip-bot for Jason Low
2015-03-07 17:13 ` Oleg Nesterov [this message]
2015-03-10 10:59 ` Peter Zijlstra
2015-03-10 16:04 ` Linus Torvalds
2015-03-10 16:16 ` Peter Zijlstra
2015-03-10 17:28 ` Oleg Nesterov
2015-03-10 17:45 ` Linus Torvalds
2015-03-10 18:33 ` Oleg Nesterov
2015-03-07 18:17 ` [PATCH] " Sasha Levin
2015-03-09 17:37 ` Jason Low
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