is it a bug of /glibc/sysdeps/arm/atomicity.h ?

[Hu, Boris]

In /glibc/sysdeps/arm/atomicity.h

 65 static inline int
 66 __attribute__ ((unused))
 67 compare_and_swap (volatile long int *p, long int oldval, long int
newval)
 68 {
 69   int result, tmp;
 70   __asm__ ("\n"
 71            "0:\tldr\t%1,[%2]\n\t"
 72            "mov\t%0,#0\n\t"
 73            "cmp\t%1,%4\n\t"
 74            "bne\t1f\n\t"
 75            "swp\t%0,%3,[%2]\n\t"
 76            "cmp\t%1,%0\n\t"
 77            "swpne\t%1,%0,[%2]\n\t"
 78            "bne\t0b\n\t"
 79            "mov\t%0,#1\n"
 80            "1:"
 81            : "=&r" (result), "=&r" (tmp)
 82            : "r" (p), "r" (newval), "r" (oldval)
 83            : "cc", "memory");
 84   return result;
 85 }

let us consider the following scenario. Suppose there are three thread
pathes. 
Init:   *p = 0
T1 compare_and_swap(p, 0, 1) ; 
T2 compare_and_swap(p,0,1); 
T3 compare_and_swap(p,1,2);

T1::
static inline int  compare_and_swap (volatile long int *p, 
 long int oldval, long int newval)
 {
	int result, tmp;
     	__asm__ ("\n"
     	"0:\tldr\t%1,[%2]\n\t"
              	"mov\t%0,#0\n\t"
              	"cmp\t%1,%4\n\t"
              	"bne\t1f\n\t"              // if now, in T2,  *p= 1;
              	"swp\t%0,%3,[%2]\n\t"          
              	"cmp\t%1,%0\n\t"           // if now, in T3  *p = 2
              	"swpne\t%1,%0,[%2]\n\t"    // *p = 1 ; so the modification
of T3 will be overwritten.  ???
              	"bne\t0b\n\t"
              	"mov\t%0,#1\n"
              	"1:"
              	: "=&r" (result), "=&r" (tmp)
              	: "r" (p), "r" (newval), "r" (oldval)
              	: "cc", "memory");
     	return result;
}

any opinion? thanks. 


  Boris
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