From: Peter Zijlstra <peterz@infradead.org>
To: Marco Elver <elver@google.com>
Cc: Qian Cai <cai@lca.pw>, Will Deacon <will@kernel.org>,
mingo@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next
Date: Thu, 23 Jan 2020 10:36:04 +0100 [thread overview]
Message-ID: <20200123093604.GT14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200122223851.GA45602@google.com>
On Wed, Jan 22, 2020 at 11:38:51PM +0100, Marco Elver wrote:
> If possible, decode and get the line numbers. I have observed a data
> race in osq_lock before, however, this is the only one I have recently
> seen in osq_lock:
>
> read to 0xffff88812c12d3d4 of 4 bytes by task 23304 on cpu 0:
> osq_lock+0x170/0x2f0 kernel/locking/osq_lock.c:143
>
> while (!READ_ONCE(node->locked)) {
> /*
> * If we need to reschedule bail... so we can block.
> * Use vcpu_is_preempted() to avoid waiting for a preempted
> * lock holder:
> */
> --> if (need_resched() || vcpu_is_preempted(node_cpu(node->prev)))
> goto unqueue;
>
> cpu_relax();
> }
>
> where
>
> static inline int node_cpu(struct optimistic_spin_node *node)
> {
> --> return node->cpu - 1;
> }
>
>
> write to 0xffff88812c12d3d4 of 4 bytes by task 23334 on cpu 1:
> osq_lock+0x89/0x2f0 kernel/locking/osq_lock.c:99
>
> bool osq_lock(struct optimistic_spin_queue *lock)
> {
> struct optimistic_spin_node *node = this_cpu_ptr(&osq_node);
> struct optimistic_spin_node *prev, *next;
> int curr = encode_cpu(smp_processor_id());
> int old;
>
> node->locked = 0;
> node->next = NULL;
> --> node->cpu = curr;
>
Yeah, that's impossible. This store happens before the node is
published, so no matter how the load in node_cpu() is shattered, it must
observe the right value.
next prev parent reply other threads:[~2020-01-23 9:36 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 16:38 [PATCH] locking/osq_lock: fix a data race in osq_wait_next Qian Cai
2020-01-22 16:59 ` Will Deacon
2020-01-22 17:08 ` Qian Cai
2020-01-22 22:38 ` Marco Elver
2020-01-22 23:54 ` Qian Cai
2020-01-23 9:39 ` Peter Zijlstra
2020-01-28 3:11 ` Qian Cai
2020-01-28 11:46 ` Marco Elver
2020-01-28 12:53 ` Qian Cai
2020-01-28 16:52 ` Peter Zijlstra
2020-01-28 16:56 ` Peter Zijlstra
2020-01-29 0:22 ` Paul E. McKenney
2020-01-29 15:29 ` Marco Elver
2020-01-29 18:40 ` Peter Zijlstra
2020-01-30 13:39 ` Marco Elver
2020-01-30 13:48 ` Peter Zijlstra
2020-01-31 3:32 ` Qian Cai
2020-01-29 18:49 ` Peter Zijlstra
2020-01-29 19:26 ` Paul E. McKenney
2020-01-23 9:36 ` Peter Zijlstra [this message]
2020-01-28 3:12 ` Qian Cai
2020-01-28 8:18 ` Marco Elver
2020-01-28 10:10 ` Qian Cai
2020-01-28 10:29 ` Marco Elver
2020-01-22 17:09 ` Peter Zijlstra
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