From: Nicholas Piggin <npiggin@gmail.com>
To: Andy Lutomirski <luto@kernel.org>, x86@kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm
Date: Wed, 16 Jun 2021 14:28:54 +1000 [thread overview]
Message-ID: <1623817648.jh19a97b5a.astroid@bobo.none> (raw)
In-Reply-To: <74ace142f48db7d0e71b05b5ace72bfe8e0a2652.1623813516.git.luto@kernel.org>
Excerpts from Andy Lutomirski's message of June 16, 2021 1:21 pm:
> membarrier reads cpu_rq(remote cpu)->curr->mm without locking. Use
> READ_ONCE() and WRITE_ONCE() to remove the data races.
>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> fs/exec.c | 2 +-
> kernel/kthread.c | 4 ++--
> kernel/sched/membarrier.c | 6 +++---
> 3 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 18594f11c31f..2e63dea83411 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1007,7 +1007,7 @@ static int exec_mmap(struct mm_struct *mm)
> local_irq_disable();
> active_mm = tsk->active_mm;
> tsk->active_mm = mm;
> - tsk->mm = mm;
> + WRITE_ONCE(tsk->mm, mm); /* membarrier reads this without locks */
> /*
> * This prevents preemption while active_mm is being loaded and
> * it and mm are being updated, which could cause problems for
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 8275b415acec..4962794e02d5 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -1322,7 +1322,7 @@ void kthread_use_mm(struct mm_struct *mm)
> mmgrab(mm);
> tsk->active_mm = mm;
> }
> - tsk->mm = mm;
> + WRITE_ONCE(tsk->mm, mm); /* membarrier reads this without locks */
> membarrier_update_current_mm(mm);
> switch_mm_irqs_off(active_mm, mm, tsk);
> membarrier_finish_switch_mm(atomic_read(&mm->membarrier_state));
> @@ -1363,7 +1363,7 @@ void kthread_unuse_mm(struct mm_struct *mm)
> smp_mb__after_spinlock();
> sync_mm_rss(mm);
> local_irq_disable();
> - tsk->mm = NULL;
> + WRITE_ONCE(tsk->mm, NULL); /* membarrier reads this without locks */
> membarrier_update_current_mm(NULL);
> /* active_mm is still 'mm' */
> enter_lazy_tlb(mm, tsk);
> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> index 3173b063d358..c32c32a2441e 100644
> --- a/kernel/sched/membarrier.c
> +++ b/kernel/sched/membarrier.c
> @@ -410,7 +410,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
> goto out;
> rcu_read_lock();
> p = rcu_dereference(cpu_rq(cpu_id)->curr);
> - if (!p || p->mm != mm) {
> + if (!p || READ_ONCE(p->mm) != mm) {
> rcu_read_unlock();
> goto out;
> }
> @@ -423,7 +423,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
> struct task_struct *p;
>
> p = rcu_dereference(cpu_rq(cpu)->curr);
> - if (p && p->mm == mm)
> + if (p && READ_ONCE(p->mm) == mm)
/* exec, kthread_use_mm write this without locks */ ?
Seems good to me.
Acked-by: Nicholas Piggin <npiggin@gmail.com>
> __cpumask_set_cpu(cpu, tmpmask);
> }
> rcu_read_unlock();
> @@ -521,7 +521,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm)
> struct task_struct *p;
>
> p = rcu_dereference(rq->curr);
> - if (p && p->mm == mm)
> + if (p && READ_ONCE(p->mm) == mm)
> __cpumask_set_cpu(cpu, tmpmask);
> }
> rcu_read_unlock();
> --
> 2.31.1
>
>
next prev parent reply other threads:[~2021-06-16 4:29 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-16 3:21 [PATCH 0/8] membarrier cleanups Andy Lutomirski
2021-06-16 3:21 ` [PATCH 1/8] membarrier: Document why membarrier() works Andy Lutomirski
2021-06-16 4:00 ` Nicholas Piggin
2021-06-16 7:30 ` Peter Zijlstra
2021-06-17 23:45 ` Andy Lutomirski
2021-06-16 3:21 ` [PATCH 2/8] x86/mm: Handle unlazying membarrier core sync in the arch code Andy Lutomirski
2021-06-16 4:25 ` Nicholas Piggin
2021-06-16 18:31 ` Andy Lutomirski
2021-06-16 17:49 ` Mathieu Desnoyers
2021-06-16 18:31 ` Andy Lutomirski
2021-06-16 3:21 ` [PATCH 3/8] membarrier: Remove membarrier_arch_switch_mm() prototype in core code Andy Lutomirski
2021-06-16 4:26 ` Nicholas Piggin
2021-06-16 17:52 ` Mathieu Desnoyers
2021-06-16 3:21 ` [PATCH 4/8] membarrier: Make the post-switch-mm barrier explicit Andy Lutomirski
2021-06-16 4:19 ` Nicholas Piggin
2021-06-16 7:35 ` Peter Zijlstra
2021-06-16 18:41 ` Andy Lutomirski
2021-06-17 1:37 ` Nicholas Piggin
2021-06-17 2:57 ` Andy Lutomirski
2021-06-17 5:32 ` Andy Lutomirski
2021-06-17 6:51 ` Nicholas Piggin
2021-06-17 23:49 ` Andy Lutomirski
2021-06-19 2:53 ` Nicholas Piggin
2021-06-19 3:20 ` Andy Lutomirski
2021-06-19 4:27 ` Nicholas Piggin
2021-06-17 9:08 ` [RFC][PATCH] sched: Use lightweight hazard pointers to grab lazy mms Peter Zijlstra
2021-06-17 9:10 ` Peter Zijlstra
2021-06-17 10:00 ` Nicholas Piggin
2021-06-17 9:13 ` Peter Zijlstra
2021-06-17 14:06 ` Andy Lutomirski
2021-06-17 9:28 ` Peter Zijlstra
2021-06-17 14:03 ` Andy Lutomirski
2021-06-17 14:10 ` Andy Lutomirski
2021-06-17 15:45 ` Peter Zijlstra
2021-06-18 3:29 ` Paul E. McKenney
2021-06-18 5:04 ` Andy Lutomirski
2021-06-17 15:02 ` [PATCH 4/8] membarrier: Make the post-switch-mm barrier explicit Paul E. McKenney
2021-06-18 0:06 ` Andy Lutomirski
2021-06-18 3:35 ` Paul E. McKenney
2021-06-17 8:45 ` Peter Zijlstra
2021-06-16 3:21 ` [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm Andy Lutomirski
2021-06-16 4:28 ` Nicholas Piggin [this message]
2021-06-16 18:08 ` Mathieu Desnoyers
2021-06-16 18:45 ` Andy Lutomirski
2021-06-16 3:21 ` [PATCH 6/8] powerpc/membarrier: Remove special barrier on mm switch Andy Lutomirski
2021-06-16 4:36 ` Nicholas Piggin
2021-06-16 3:21 ` [PATCH 7/8] membarrier: Remove arm (32) support for SYNC_CORE Andy Lutomirski
2021-06-16 9:28 ` Russell King (Oracle)
2021-06-16 10:16 ` Peter Zijlstra
2021-06-16 10:20 ` Peter Zijlstra
2021-06-16 10:34 ` Russell King (Oracle)
2021-06-16 11:10 ` Peter Zijlstra
2021-06-16 13:22 ` Russell King (Oracle)
2021-06-16 15:04 ` Catalin Marinas
2021-06-16 15:23 ` Russell King (Oracle)
2021-06-16 15:45 ` Catalin Marinas
2021-06-16 16:00 ` Catalin Marinas
2021-06-16 16:27 ` Russell King (Oracle)
2021-06-17 8:55 ` Krzysztof Hałasa
2021-06-18 12:54 ` Linus Walleij
2021-06-18 13:19 ` Russell King (Oracle)
2021-06-18 13:36 ` Arnd Bergmann
2021-06-17 10:40 ` Mark Rutland
2021-06-17 11:23 ` Russell King (Oracle)
2021-06-17 11:33 ` Mark Rutland
2021-06-17 13:41 ` Andy Lutomirski
2021-06-17 13:51 ` Mark Rutland
2021-06-17 14:00 ` Andy Lutomirski
2021-06-17 14:20 ` Mark Rutland
2021-06-17 15:01 ` Peter Zijlstra
2021-06-17 15:13 ` Peter Zijlstra
2021-06-17 14:16 ` Mathieu Desnoyers
2021-06-17 14:05 ` Peter Zijlstra
2021-06-18 0:07 ` Andy Lutomirski
2021-06-16 3:21 ` [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and improve documentation Andy Lutomirski
2021-06-16 4:45 ` Nicholas Piggin
2021-06-16 18:52 ` Andy Lutomirski
2021-06-16 23:48 ` Andy Lutomirski
2021-06-18 15:27 ` Christophe Leroy
2021-06-16 10:20 ` Will Deacon
2021-06-16 23:58 ` Andy Lutomirski
2021-06-17 14:47 ` Mathieu Desnoyers
2021-06-18 0:12 ` Andy Lutomirski
2021-06-18 16:31 ` Mathieu Desnoyers
2021-06-18 19:58 ` Andy Lutomirski
2021-06-18 20:09 ` Mathieu Desnoyers
2021-06-19 6:02 ` Nicholas Piggin
2021-06-19 15:50 ` Andy Lutomirski
2021-06-20 2:10 ` Nicholas Piggin
2021-06-17 15:16 ` Mathieu Desnoyers
2021-06-18 0:13 ` Andy Lutomirski
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