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Date:: Thu Jan 16 16:54:19 2020 UTC
Message:: malloc: remove locking The issue manifests in fork: POSIX fork mandates that a fork'd process is created with a single thread. If a multithreaded program forks, and some thread was in malloc() when the fork() happened, then in the child the lock will be held but there will be no thread to release it. We assume the system malloc() must already know how to deal with this and is thread-safe, but it won't know about our custom spinlock. Judging that this is no longer necessary (the lock code was added 15 years ago) we remove it. Signed-off-by: Dan Cross <cross@gajendra.net>
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  1 9c635587 2004-06-09 devnull #include <u.h>
  2 9c635587 2004-06-09 devnull #define NOPLAN9DEFINES
  3 9c635587 2004-06-09 devnull #include <libc.h>
  4 9c635587 2004-06-09 devnull 
  5 9c635587 2004-06-09 devnull /*
  6 9c635587 2004-06-09 devnull  * The Unix libc routines cannot be trusted to do their own locking.
  7 9c635587 2004-06-09 devnull  * Sad but apparently true.
  8 9c635587 2004-06-09 devnull  */
  9 9c635587 2004-06-09 devnull static int mallocpid;
 10 9c635587 2004-06-09 devnull 
 11 9c635587 2004-06-09 devnull /*
 12 9c635587 2004-06-09 devnull  * The Unix mallocs don't do nearly enough error checking
 13 9c635587 2004-06-09 devnull  * for my tastes.  We'll waste another 24 bytes per guy so that
 14 9c635587 2004-06-09 devnull  * we can.  This is severely antisocial, since now free and p9free
 15 9c635587 2004-06-09 devnull  * are not interchangeable.
 16 9c635587 2004-06-09 devnull  */
 17 9c635587 2004-06-09 devnull int debugmalloc;
 18 9c635587 2004-06-09 devnull 
 19 9c635587 2004-06-09 devnull #define Overhead (debugmalloc ? (6*sizeof(ulong)) : 0)
 20 9c635587 2004-06-09 devnull #define MallocMagic 0xA110C09
 21 9c635587 2004-06-09 devnull #define ReallocMagic 0xB110C09
 22 9c635587 2004-06-09 devnull #define CallocMagic 0xC110C09
 23 9c635587 2004-06-09 devnull #define FreeMagic 0xF533F533
 24 9c635587 2004-06-09 devnull #define CheckMagic 0
 25 9c635587 2004-06-09 devnull #define END "\x7F\x2E\x55\x23"
 26 9c635587 2004-06-09 devnull 
 27 9c635587 2004-06-09 devnull static void
 28 9c635587 2004-06-09 devnull whoops(void *v)
 29 9c635587 2004-06-09 devnull {
 30 9c635587 2004-06-09 devnull 	fprint(2, "bad malloc block %p\n", v);
 31 9c635587 2004-06-09 devnull 	abort();
 32 9c635587 2004-06-09 devnull }
 33 9c635587 2004-06-09 devnull 
 34 9c635587 2004-06-09 devnull static void*
 35 9c635587 2004-06-09 devnull mark(void *v, ulong pc, ulong n, ulong magic)
 36 9c635587 2004-06-09 devnull {
 37 9c635587 2004-06-09 devnull 	ulong *u;
 38 9c635587 2004-06-09 devnull 	char *p;
 39 9c635587 2004-06-09 devnull 
 40 9c635587 2004-06-09 devnull 	if(!debugmalloc)
 41 9c635587 2004-06-09 devnull 		return v;
 42 9c635587 2004-06-09 devnull 
 43 9c635587 2004-06-09 devnull 	if(v == nil)
 44 9c635587 2004-06-09 devnull 		return nil;
 45 9c635587 2004-06-09 devnull 
 46 9c635587 2004-06-09 devnull 	if(magic == FreeMagic || magic == CheckMagic){
 47 9c635587 2004-06-09 devnull 		u = (ulong*)((char*)v-4*sizeof(ulong));
 48 9c635587 2004-06-09 devnull 		if(u[0] != MallocMagic && u[0] != ReallocMagic && u[0] != CallocMagic)
 49 9c635587 2004-06-09 devnull 			whoops(v);
 50 9c635587 2004-06-09 devnull 		n = u[1];
 51 9c635587 2004-06-09 devnull 		p = (char*)v+n;
 52 9c635587 2004-06-09 devnull 		if(memcmp(p, END, 4) != 0)
 53 9c635587 2004-06-09 devnull 			whoops(v);
 54 9c635587 2004-06-09 devnull 		if(magic != CheckMagic){
 55 9c635587 2004-06-09 devnull 			u[0] = FreeMagic;
 56 9c635587 2004-06-09 devnull 			u[1] = u[2] = u[3] = pc;
 57 9c635587 2004-06-09 devnull 			if(n > 16){
 58 9c635587 2004-06-09 devnull 				u[4] = u[5] = u[6] = u[7] = pc;
 59 9c635587 2004-06-09 devnull 				memset((char*)v+16, 0xFB, n-16);
 60 9c635587 2004-06-09 devnull 			}
 61 9c635587 2004-06-09 devnull 		}
 62 9c635587 2004-06-09 devnull 		return u;
 63 9c635587 2004-06-09 devnull 	}else{
 64 9c635587 2004-06-09 devnull 		u = v;
 65 9c635587 2004-06-09 devnull 		u[0] = magic;
 66 9c635587 2004-06-09 devnull 		u[1] = n;
 67 9c635587 2004-06-09 devnull 		u[2] = 0;
 68 9c635587 2004-06-09 devnull 		u[3] = 0;
 69 9c635587 2004-06-09 devnull 		if(magic == ReallocMagic)
 70 9c635587 2004-06-09 devnull 			u[3] = pc;
 71 9c635587 2004-06-09 devnull 		else
 72 9c635587 2004-06-09 devnull 			u[2] = pc;
 73 9c635587 2004-06-09 devnull 		p = (char*)(u+4)+n;
 74 9c635587 2004-06-09 devnull 		memmove(p, END, 4);
 75 9c635587 2004-06-09 devnull 		return u+4;
 76 fa325e9b 2020-01-10 cross 	}
 77 9c635587 2004-06-09 devnull }
 78 9c635587 2004-06-09 devnull 
 79 9c635587 2004-06-09 devnull void
 80 9c635587 2004-06-09 devnull setmalloctag(void *v, ulong t)
 81 9c635587 2004-06-09 devnull {
 82 9c635587 2004-06-09 devnull 	ulong *u;
 83 9c635587 2004-06-09 devnull 
 84 9c635587 2004-06-09 devnull 	if(!debugmalloc)
 85 9c635587 2004-06-09 devnull 		return;
 86 9c635587 2004-06-09 devnull 
 87 9c635587 2004-06-09 devnull 	if(v == nil)
 88 9c635587 2004-06-09 devnull 		return;
 89 9c635587 2004-06-09 devnull 	u = mark(v, 0, 0, 0);
 90 9c635587 2004-06-09 devnull 	u[2] = t;
 91 9c635587 2004-06-09 devnull }
 92 9c635587 2004-06-09 devnull 
 93 9c635587 2004-06-09 devnull void
 94 9c635587 2004-06-09 devnull setrealloctag(void *v, ulong t)
 95 9c635587 2004-06-09 devnull {
 96 9c635587 2004-06-09 devnull 	ulong *u;
 97 9c635587 2004-06-09 devnull 
 98 9c635587 2004-06-09 devnull 	if(!debugmalloc)
 99 9c635587 2004-06-09 devnull 		return;
100 9c635587 2004-06-09 devnull 
101 9c635587 2004-06-09 devnull 	if(v == nil)
102 9c635587 2004-06-09 devnull 		return;
103 9c635587 2004-06-09 devnull 	u = mark(v, 0, 0, 0);
104 9c635587 2004-06-09 devnull 	u[3] = t;
105 9c635587 2004-06-09 devnull }
106 fa325e9b 2020-01-10 cross 
107 9c635587 2004-06-09 devnull void*
108 9c635587 2004-06-09 devnull p9malloc(ulong n)
109 9c635587 2004-06-09 devnull {
110 9c635587 2004-06-09 devnull 	void *v;
111 9c635587 2004-06-09 devnull 	if(n == 0)
112 9c635587 2004-06-09 devnull 		n++;
113 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d malloc\n", argv0, getpid()); */
114 9c635587 2004-06-09 devnull 	mallocpid = getpid();
115 9c635587 2004-06-09 devnull 	v = malloc(n+Overhead);
116 9c635587 2004-06-09 devnull 	v = mark(v, getcallerpc(&n), n, MallocMagic);
117 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d donemalloc\n", argv0, getpid()); */
118 9c635587 2004-06-09 devnull 	return v;
119 9c635587 2004-06-09 devnull }
120 9c635587 2004-06-09 devnull 
121 9c635587 2004-06-09 devnull void
122 9c635587 2004-06-09 devnull p9free(void *v)
123 9c635587 2004-06-09 devnull {
124 9c635587 2004-06-09 devnull 	if(v == nil)
125 9c635587 2004-06-09 devnull 		return;
126 9c635587 2004-06-09 devnull 
127 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d free\n", argv0, getpid()); */
128 9c635587 2004-06-09 devnull 	mallocpid = getpid();
129 9c635587 2004-06-09 devnull 	v = mark(v, getcallerpc(&v), 0, FreeMagic);
130 9c635587 2004-06-09 devnull 	free(v);
131 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d donefree\n", argv0, getpid()); */
132 9c635587 2004-06-09 devnull }
133 9c635587 2004-06-09 devnull 
134 9c635587 2004-06-09 devnull void*
135 9c635587 2004-06-09 devnull p9calloc(ulong a, ulong b)
136 9c635587 2004-06-09 devnull {
137 9c635587 2004-06-09 devnull 	void *v;
138 9c635587 2004-06-09 devnull 
139 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d calloc\n", argv0, getpid()); */
140 9c635587 2004-06-09 devnull 	mallocpid = getpid();
141 9c635587 2004-06-09 devnull 	v = calloc(a*b+Overhead, 1);
142 9c635587 2004-06-09 devnull 	v = mark(v, getcallerpc(&a), a*b, CallocMagic);
143 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d donecalloc\n", argv0, getpid()); */
144 9c635587 2004-06-09 devnull 	return v;
145 9c635587 2004-06-09 devnull }
146 9c635587 2004-06-09 devnull 
147 9c635587 2004-06-09 devnull void*
148 9c635587 2004-06-09 devnull p9realloc(void *v, ulong n)
149 9c635587 2004-06-09 devnull {
150 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d realloc\n", argv0, getpid()); */
151 9c635587 2004-06-09 devnull 	mallocpid = getpid();
152 9c635587 2004-06-09 devnull 	v = mark(v, getcallerpc(&v), 0, CheckMagic);
153 9c635587 2004-06-09 devnull 	v = realloc(v, n+Overhead);
154 9c635587 2004-06-09 devnull 	v = mark(v, getcallerpc(&v), n, ReallocMagic);
155 cbeb0b26 2006-04-01 devnull /*fprint(2, "%s %d donerealloc\n", argv0, getpid()); */
156 9c635587 2004-06-09 devnull 	return v;
157 9c635587 2004-06-09 devnull }