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From: Andi Kleen <ak@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Luck, Tony" <tony.luck@intel.com>,
	Jeremy Cline <jcline@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org, Laura Abbott <labbott@redhat.com>
Subject: x86/mce: suspicious RCU usage in 4.13.4
Date: Wed, 11 Oct 2017 16:11:37 -0700	[thread overview]
Message-ID: <20171011231137.GI5109@tassilo.jf.intel.com> (raw)

> -	next = mce_log_get_idx_check(mcelog.next);
> +	next = mcelog.next;
>  
>  	/* Only supports full reads right now */
>  	err = -EINVAL;
> @@ -281,8 +266,6 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
>  		next = cmpxchg(&mcelog.next, prev, 0);
>  	} while (next != prev);
>  
> -	synchronize_sched();

Sorry I take back what I wrote earlier. This RCU is actually still needed,
otherwise the reader could see partially written entries.

So rather have to keep that, and change the read code to run with rcu_read_lock()

-Andi
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WARNING: multiple messages have this Message-ID (diff)
From: Andi Kleen <ak@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Luck, Tony" <tony.luck@intel.com>,
	Jeremy Cline <jcline@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org, Laura Abbott <labbott@redhat.com>
Subject: Re: x86/mce: suspicious RCU usage in 4.13.4
Date: Wed, 11 Oct 2017 16:11:37 -0700	[thread overview]
Message-ID: <20171011231137.GI5109@tassilo.jf.intel.com> (raw)
In-Reply-To: <20171011115020.i4gkcy5pjifh2zsm@pd.tnic>

> -	next = mce_log_get_idx_check(mcelog.next);
> +	next = mcelog.next;
>  
>  	/* Only supports full reads right now */
>  	err = -EINVAL;
> @@ -281,8 +266,6 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
>  		next = cmpxchg(&mcelog.next, prev, 0);
>  	} while (next != prev);
>  
> -	synchronize_sched();

Sorry I take back what I wrote earlier. This RCU is actually still needed,
otherwise the reader could see partially written entries.

So rather have to keep that, and change the read code to run with rcu_read_lock()

-Andi

             reply	other threads:[~2017-10-11 23:11 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-11 23:11 Andi Kleen [this message]
2017-10-11 23:11 ` x86/mce: suspicious RCU usage in 4.13.4 Andi Kleen
  -- strict thread matches above, loose matches on Subject: below --
2017-11-01 20:07 Luck, Tony
2017-11-01 20:07 ` Luck, Tony
2017-11-01 16:47 Borislav Petkov
2017-11-01 16:47 ` Borislav Petkov
2017-11-01 20:28 ` [tip:ras/urgent] x86/mcelog: Get rid of RCU remnants tip-bot for Borislav Petkov
2017-11-01 14:56 x86/mce: suspicious RCU usage in 4.13.4 Laura Abbott
2017-11-01 14:56 ` Laura Abbott
2017-10-16 18:28 Luck, Tony
2017-10-16 18:28 ` Luck, Tony
2017-10-15  9:40 Borislav Petkov
2017-10-15  9:40 ` Borislav Petkov
2017-10-12 22:13 Andi Kleen
2017-10-12 22:13 ` Andi Kleen
2017-10-12  9:02 Borislav Petkov
2017-10-12  9:02 ` Borislav Petkov
2017-10-11 21:34 Luck, Tony
2017-10-11 21:34 ` Luck, Tony
2017-10-11 11:50 Borislav Petkov
2017-10-11 11:50 ` Borislav Petkov
2017-10-10 20:13 Andi Kleen
2017-10-10 20:13 ` Andi Kleen
2017-10-10 20:08 Luck, Tony
2017-10-10 20:08 ` Luck, Tony
2017-10-10 19:44 Borislav Petkov
2017-10-10 19:44 ` Borislav Petkov
2017-10-10 19:00 Jeremy Cline

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