linux-kernel - Re: [PATCH] x86/spinlocks: Fix regression in spinlock contention detection

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 for Android: free password hash cracker in your pocket

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

Date:	Tue, 05 May 2015 20:55:25 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Tahsin Erdogan <tahsin@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, Waiman.Long@...com, borntraeger@...ibm.com,
	oleg@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/spinlocks: Fix regression in spinlock contention
 detection

On 05/05/2015 07:33 PM, Tahsin Erdogan wrote:
> The conversion to signed happens with types shorter than int (__ticket_t
> is either u8 or u16).
>
> By changing Raghavendra's program to use unsigned short int, you can see
> the problem:
>
> ================
> #include <stdio.h>
>
> #define LOCK_INC 2
>
> int main()
> {
>          unsigned short int head = 32700, tail=2;
>
>          if ((tail - head) > LOCK_INC)
>                  printf(" tail - head > LOCK_INC \n");
>          else
>                  printf(" tail - head < LOCK_INC \n");
>
>          return 0;
> }
>
> ================
> gcc -g -o t main.c
> ./t
>   tail - head < LOCK_INC
>
> However, having just unsigned int returns the opposite result (unsigned
> int head = 32700, tail=2;)
>

Interestingly,

#include <stdio.h>

//#define LOCK_INC ((unsigned int)2) // case 1
#define LOCK_INC 2 //case 2

int main()
{
	unsigned short int head = 32700, tail=2;

	if ((tail - head) > LOCK_INC)
		printf(" tail - head > LOCK_INC \n");
	else
		printf(" tail - head < LOCK_INC \n");

	return 0;
}

case 1 works here (PeterZ's stricter version)

case 2 gives tail - head < LOCK_INC

But is it not that we have case 1 we are looking here ?


--
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/