linux-kernel - Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing completions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <54DCB7E6.8040802@linux.vnet.ibm.com>
Date:	Thu, 12 Feb 2015 19:55:42 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	peterz@...radead.org, torvalds@...ux-foundation.org,
	konrad.wilk@...cle.com, pbonzini@...hat.com,
	paulmck@...ux.vnet.ibm.com, waiman.long@...com, davej@...hat.com,
	x86@...nel.org, jeremy@...p.org, paul.gortmaker@...driver.com,
	ak@...ux.intel.com, jasowang@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, riel@...hat.com,
	borntraeger@...ibm.com, akpm@...ux-foundation.org,
	a.ryabinin@...sung.com, sasha.levin@...cle.com, dave@...olabs.net
Subject: Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing
 completions

On 02/12/2015 07:32 PM, Oleg Nesterov wrote:
> Damn, sorry for noise, forgot to mention...
>
> On 02/12, Raghavendra K T wrote:
>>
>> +static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
>> +							__ticket_t head)
>> +{
>> +	if (head & TICKET_SLOWPATH_FLAG) {
>> +		arch_spinlock_t old, new;
>> +
>> +		old.tickets.head = head;
>> +		new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
>> +		old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
>> +		new.tickets.tail = old.tickets.tail;
>> +
>> +		/* try to clear slowpath flag when there are no contenders */
>> +		cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
>> +	}
>> +}
>
> ...
>
>> +clear_slowpath:
>> +	if (TICKET_SLOWPATH_FLAG)
>> +		__ticket_check_and_clear_slowpath(lock, inc.head);
>
> I think you can remove this "if (TICKET_SLOWPATH_FLAG)" check. If it is
> defined as zero, gcc should optimize out the code under "if (head & 0)".
>

right, the above if ( ) is unnecesary, though we would have same code
at the end, getting rid of that makes code more clean.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/