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Further improve mmap() locking story

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The way to use double linked lists, is to remove all the things you want
to work on, insert them into a new list on the stack. Then once you have
all the work items, you release the lock, do your work, and then lock it
again, to add the shelled out items back to a global freelist.
This commit is contained in:
Justine Tunney 2024-06-29 17:12:25 -07:00
parent 98e684622b
commit 1bf2d8e308
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GPG key ID: BE714B4575D6E328
8 changed files with 84 additions and 101 deletions
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145
libc/intrin/mmap.c
View file

@ -21,6 +21,7 @@
#include "libc/calls/blockcancel.internal.h"
#include "libc/calls/calls.h"
#include "libc/calls/internal.h"
#include "libc/calls/state.internal.h"
#include "libc/calls/struct/sigset.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/dce.h"
@ -187,10 +188,10 @@ int __munmap(char *addr, size_t size, bool untrack_only) {
!size || (uintptr_t)addr + size < size)
return einval();
// untrack and delete mapping
// untrack mappings
int rc = 0;
struct Dll *delete = 0;
__maps_lock();
StartOver:;
struct Map *map = __maps.maps;
struct Map **prev = &__maps.maps;
while (map) {
@ -202,30 +203,10 @@ StartOver:;
if (addr <= map_addr && addr + PGUP(size) >= map_addr + PGUP(map_size)) {
// remove mapping completely
dll_remove(&__maps.used, &map->elem);
dll_make_first(&delete, &map->elem);
*prev = next;
__maps.pages -= (map_size + pagesz - 1) / pagesz;
__maps.count -= 1;
if (untrack_only) {
__maps_free(map);
__maps_check();
} else {
__maps_unlock();
if (!IsWindows()) {
ASSERT(addr <= map_addr);
ASSERT(map_addr + PGUP(map_size) <= addr + PGUP(size));
if (sys_munmap(map_addr, map_size))
rc = -1;
} else {
if (!UnmapViewOfFile(map_addr))
rc = -1;
if (!CloseHandle(map->h))
rc = -1;
}
__maps_lock();
__maps_free(map);
__maps_check();
goto StartOver;
}
map = next;
continue;
} else if (IsWindows()) {
@ -240,35 +221,34 @@ StartOver:;
size_t right = map_size - left;
ASSERT(right > 0);
ASSERT(left > 0);
map->addr += left;
map->size = right;
if (!(map->flags & MAP_ANONYMOUS))
map->off += left;
__maps.pages -= (left + pagesz - 1) / pagesz;
__maps_check();
if (!untrack_only) {
__maps_unlock();
ASSERT(addr <= map_addr);
ASSERT(map_addr + PGUP(left) <= addr + PGUP(size));
if (sys_munmap(map_addr, left) == -1)
rc = -1;
__maps_lock();
goto StartOver;
struct Map *leftmap;
if ((leftmap = __maps_alloc())) {
map->addr += left;
map->size = right;
if (!(map->flags & MAP_ANONYMOUS))
map->off += left;
__maps.pages -= (left + pagesz - 1) / pagesz;
__maps_check();
leftmap->addr = map_addr;
leftmap->size = left;
dll_make_first(&delete, &leftmap->elem);
} else {
rc = -1;
}
} else if (addr + PGUP(size) >= map_addr + PGUP(map_size)) {
// shave off righthand side of mapping
size_t left = addr - map_addr;
size_t right = map_addr + map_size - addr;
map->size = left;
__maps.pages -= (right + pagesz - 1) / pagesz;
__maps_check();
if (!untrack_only) {
__maps_unlock();
ASSERT(PGUP(right) <= PGUP(size));
if (sys_munmap(addr, right) == -1)
rc = -1;
__maps_lock();
goto StartOver;
struct Map *rightmap;
if ((rightmap = __maps_alloc())) {
map->size = left;
__maps.pages -= (right + pagesz - 1) / pagesz;
__maps_check();
rightmap->addr = addr;
rightmap->size = right;
dll_make_first(&delete, &rightmap->elem);
} else {
rc = -1;
}
} else {
// punch hole in mapping
@ -277,27 +257,28 @@ StartOver:;
size_t right = map_size - middle - left;
struct Map *leftmap;
if ((leftmap = __maps_alloc())) {
leftmap->next = map;
leftmap->addr = map_addr;
leftmap->size = left;
leftmap->off = map->off;
leftmap->prot = map->prot;
leftmap->flags = map->flags;
map->addr += left + middle;
map->size = right;
if (!(map->flags & MAP_ANONYMOUS))
map->off += left + middle;
dll_make_first(&__maps.used, &leftmap->elem);
*prev = leftmap;
__maps.pages -= (middle + pagesz - 1) / pagesz;
__maps.count += 1;
__maps_check();
if (!untrack_only) {
__maps_unlock();
if (sys_munmap(addr, size) == -1)
rc = -1;
__maps_lock();
goto StartOver;
struct Map *middlemap;
if ((middlemap = __maps_alloc())) {
leftmap->next = map;
leftmap->addr = map_addr;
leftmap->size = left;
leftmap->off = map->off;
leftmap->prot = map->prot;
leftmap->flags = map->flags;
map->addr += left + middle;
map->size = right;
if (!(map->flags & MAP_ANONYMOUS))
map->off += left + middle;
dll_make_first(&__maps.used, &leftmap->elem);
*prev = leftmap;
__maps.pages -= (middle + pagesz - 1) / pagesz;
__maps.count += 1;
__maps_check();
middlemap->addr = addr;
middlemap->size = size;
dll_make_first(&delete, &middlemap->elem);
} else {
rc = -1;
}
} else {
rc = -1;
@ -309,6 +290,34 @@ StartOver:;
}
__maps_unlock();
// delete mappings
for (struct Dll *e = dll_first(delete); e; e = dll_next(delete, e)) {
map = MAP_CONTAINER(e);
if (!untrack_only) {
if (!IsWindows()) {
if (sys_munmap(map->addr, map->size))
rc = -1;
} else {
if (!UnmapViewOfFile(map->addr))
rc = -1;
if (!CloseHandle(map->h))
rc = -1;
}
}
}
// free mappings
if (!dll_is_empty(delete)) {
__maps_lock();
struct Dll *e;
while ((e = dll_first(delete))) {
dll_remove(&delete, e);
__maps_free(MAP_CONTAINER(e));
}
__maps_check();
__maps_unlock();
}
return rc;
}