From: Jason Wang <jasowang@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
"Michael S. Tsirkin" <mst@redhat.com>,
Juri Lelli <jlelli@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>, He Zhe <zhe.he@windriver.com>
Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal()
Date: Thu, 15 Jul 2021 12:14:36 +0800 [thread overview]
Message-ID: <4b53e2be-c38e-7509-dfcf-94f5bf5dcc10@redhat.com> (raw)
In-Reply-To: <475f84e2-78ee-1a24-ef57-b16c1f2651ed@redhat.com>
在 2021/7/14 下午6:35, Paolo Bonzini 写道:
> On 14/07/21 11:23, Jason Wang wrote:
>>> This was added in 2020, so it's unlikely to be the direct cause of the
>>> change. What is a known-good version for the host?
>>>
>>> Since it is not KVM stuff, I'm CCing Michael and Jason.
>>
>> I think this can be probably fixed here:
>>
>> https://lore.kernel.org/lkml/20210618084412.18257-1-zhe.he@windriver.com/
>>
>
> That seems wrong; in particular it wouldn't protect against AB/BA
> deadlocks.
> In fact, the bug is with the locking; the code assumes that
> spin_lock_irqsave/spin_unlock_irqrestore is non-preemptable and therefore
> increments and decrements the percpu variable inside the critical
> section.
>
> This obviously does not fly with PREEMPT_RT; the right fix should be
> using a local_lock. Something like this (untested!!):
>
> --------------- 8< ---------------
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [PATCH] eventfd: protect eventfd_wake_count with a local_lock
>
> eventfd_signal assumes that spin_lock_irqsave/spin_unlock_irqrestore is
> non-preemptable and therefore increments and decrements the percpu
> variable inside the critical section.
>
> This obviously does not fly with PREEMPT_RT. If eventfd_signal is
> preempted and an unrelated thread calls eventfd_signal, the result is
> a spurious WARN. To avoid this, protect the percpu variable with a
> local_lock.
But local_lock only disable migration not preemption.
Or anything I missed here?
Thanks
>
> Reported-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> Fixes: b5e683d5cab8 ("eventfd: track eventfd_signal() recursion depth")
> Cc: stable@vger.kernel.org
> Cc: He Zhe <zhe.he@windriver.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
> diff --git a/fs/eventfd.c b/fs/eventfd.c
> index e265b6dd4f34..7d27b6e080ea 100644
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -12,6 +12,7 @@
> #include <linux/fs.h>
> #include <linux/sched/signal.h>
> #include <linux/kernel.h>
> +#include <linux/local_lock.h>
> #include <linux/slab.h>
> #include <linux/list.h>
> #include <linux/spinlock.h>
> @@ -25,6 +26,7 @@
> #include <linux/idr.h>
> #include <linux/uio.h>
>
> +static local_lock_t eventfd_wake_lock =
> INIT_LOCAL_LOCK(eventfd_wake_lock);
> DEFINE_PER_CPU(int, eventfd_wake_count);
>
> static DEFINE_IDA(eventfd_ida);
> @@ -71,8 +73,11 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
> * it returns true, the eventfd_signal() call should be deferred
> to a
> * safe context.
> */
> - if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count)))
> + local_lock(&eventfd_wake_lock);
> + if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) {
> + local_unlock(&eventfd_wake_lock);
> return 0;
> + }
>
> spin_lock_irqsave(&ctx->wqh.lock, flags);
> this_cpu_inc(eventfd_wake_count);
> @@ -83,6 +88,7 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
> wake_up_locked_poll(&ctx->wqh, EPOLLIN);
> this_cpu_dec(eventfd_wake_count);
> spin_unlock_irqrestore(&ctx->wqh.lock, flags);
> + local_unlock(&eventfd_wake_lock);
>
> return n;
> }
>
next prev parent reply other threads:[~2021-07-15 4:14 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 8:01 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal() Daniel Bristot de Oliveira
2021-07-14 8:10 ` Paolo Bonzini
2021-07-14 9:23 ` Jason Wang
2021-07-14 10:35 ` Paolo Bonzini
2021-07-14 10:41 ` Michael S. Tsirkin
2021-07-14 10:44 ` Paolo Bonzini
2021-07-14 12:20 ` Daniel Bristot de Oliveira
2021-07-15 4:14 ` Jason Wang [this message]
2021-07-15 5:58 ` Paolo Bonzini
2021-07-15 6:45 ` Jason Wang
2021-07-15 8:22 ` Daniel Bristot de Oliveira
2021-07-15 8:44 ` He Zhe
2021-07-15 9:51 ` Paolo Bonzini
2021-07-15 10:10 ` He Zhe
2021-07-15 11:05 ` Paolo Bonzini
2021-07-16 2:26 ` Jason Wang
2021-07-16 2:43 ` He Zhe
2021-07-16 2:46 ` Jason Wang
2021-07-15 9:46 ` Paolo Bonzini
2021-07-15 12:34 ` Daniel Bristot de Oliveira
[not found] ` <20210715102249.2205-1-hdanton@sina.com>
2021-07-15 12:31 ` Daniel Bristot de Oliveira
[not found] ` <20210716020611.2288-1-hdanton@sina.com>
2021-07-16 6:54 ` Paolo Bonzini
[not found] ` <20210716075539.2376-1-hdanton@sina.com>
2021-07-16 7:59 ` Paolo Bonzini
[not found] ` <20210716093725.2438-1-hdanton@sina.com>
2021-07-16 11:55 ` Paolo Bonzini
[not found] ` <20210718124219.1521-1-hdanton@sina.com>
2021-07-19 15:38 ` Paolo Bonzini
[not found] ` <20210721070452.1008-1-hdanton@sina.com>
2021-07-21 7:25 ` Thomas Gleixner
[not found] ` <20210721101119.1103-1-hdanton@sina.com>
2021-07-21 10:59 ` Paolo Bonzini
[not found] ` <20210723022356.1301-1-hdanton@sina.com>
2021-07-23 7:59 ` Paolo Bonzini
[not found] ` <20210723094830.1375-1-hdanton@sina.com>
2021-07-23 10:56 ` Paolo Bonzini
[not found] ` <20210724043320.1654-1-hdanton@sina.com>
2021-07-26 11:03 ` Paolo Bonzini
2021-07-28 8:06 ` Thomas Gleixner
2021-07-28 10:21 ` Paolo Bonzini
2021-07-28 19:07 ` Thomas Gleixner
2021-07-29 11:01 ` [PATCH] eventfd: Make signal recursion protection a task bit Thomas Gleixner
2021-07-29 14:32 ` Daniel Bristot de Oliveira
2021-07-29 19:23 ` Daniel Bristot de Oliveira
2021-08-26 7:03 ` Jason Wang
2021-08-27 23:41 ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
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