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From: "Luck, Tony" <tony.luck@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: 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: Tue, 10 Oct 2017 13:08:41 -0700	[thread overview]
Message-ID: <20171010200841.uhniuwc7pulqgmic@intel.com> (raw)
In-Reply-To: <20171010194426.s7keveirclglx6vh@pd.tnic>

>  	for (;;) {
>  		entry = mce_log_get_idx_check(mcelog.next);

Can't this get even simpler? Do we need the loop? The mutex
will now protect us while we check to see if there is a slot
to stash this new entry. Also just say:

		entry = mcelog.next;

>  		for (;;) {
> @@ -66,10 +67,10 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
>  			 * interesting ones:
>  			 */
>  			if (entry >= MCE_LOG_LEN) {
> -				set_bit(MCE_OVERFLOW,
> -					(unsigned long *)&mcelog.flags);
> +				set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog.flags);

Need to mutex_unlock(&mce_chrdev_read_mutex); here.

>  				return NOTIFY_OK;
>  			}
> +
>  			/* Old left over entry. Skip: */
>  			if (mcelog.entry[entry].finished) {
>  				entry++;
> @@ -77,15 +78,13 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
>  			}
>  			break;
>  		}
> -		smp_rmb();
> -		next = entry + 1;
> -		if (cmpxchg(&mcelog.next, entry, next) == entry)
> -			break;

Ummm. Without this "break" how will we exit the loop (more fuel
for getting rid of the loop.

> +		mcelog.next = entry + 1;
>  	}

-Tony

WARNING: multiple messages have this Message-ID (diff)
From: "Luck, Tony" <tony.luck@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: 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: Tue, 10 Oct 2017 13:08:41 -0700	[thread overview]
Message-ID: <20171010200841.uhniuwc7pulqgmic@intel.com> (raw)

>  	for (;;) {
>  		entry = mce_log_get_idx_check(mcelog.next);

Can't this get even simpler? Do we need the loop? The mutex
will now protect us while we check to see if there is a slot
to stash this new entry. Also just say:

		entry = mcelog.next;

>  		for (;;) {
> @@ -66,10 +67,10 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
>  			 * interesting ones:
>  			 */
>  			if (entry >= MCE_LOG_LEN) {
> -				set_bit(MCE_OVERFLOW,
> -					(unsigned long *)&mcelog.flags);
> +				set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog.flags);

Need to mutex_unlock(&mce_chrdev_read_mutex); here.

>  				return NOTIFY_OK;
>  			}
> +
>  			/* Old left over entry. Skip: */
>  			if (mcelog.entry[entry].finished) {
>  				entry++;
> @@ -77,15 +78,13 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
>  			}
>  			break;
>  		}
> -		smp_rmb();
> -		next = entry + 1;
> -		if (cmpxchg(&mcelog.next, entry, next) == entry)
> -			break;

Ummm. Without this "break" how will we exit the loop (more fuel
for getting rid of the loop.

> +		mcelog.next = entry + 1;
>  	}

-Tony
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  reply	other threads:[~2017-10-10 20:08 UTC|newest]

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

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