mm, vmalloc: iterate vmap_area_list, instead of vmlist in vread/vwrite()

Now, when we hold a vmap_area_lock, va->vm can't be discarded.  So we can
safely access to va->vm when iterating a vmap_area_list with holding a
vmap_area_lock.  With this property, change iterating vmlist codes in
vread/vwrite() to iterating vmap_area_list.

There is a little difference relate to lock, because vmlist_lock is mutex,
but, vmap_area_lock is spin_lock.  It may introduce a spinning overhead
during vread/vwrite() is executing.  But, these are debug-oriented
functions, so this overhead is not real problem for common case.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 32 insertions, 16 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1bf94ad452b6..59aa328007b2 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2012,7 +2012,8 @@ static int aligned_vwrite(char *buf, char *addr, unsigned long count)
 
 long vread(char *buf, char *addr, unsigned long count)
 {
-        struct vm_struct *tmp;
+        struct vmap_area *va;
+        struct vm_struct *vm;
         char *vaddr, *buf_start = buf;
         unsigned long buflen = count;
         unsigned long n;
@@ -2021,10 +2022,17 @@ long vread(char *buf, char *addr, unsigned long count)
         if ((unsigned long) addr + count < count)
                 count = -(unsigned long) addr;
 
-        read_lock(&vmlist_lock);
-        for (tmp = vmlist; count && tmp; tmp = tmp->next) {
-                vaddr = (char *) tmp->addr;
-                if (addr >= vaddr + tmp->size - PAGE_SIZE)
+        spin_lock(&vmap_area_lock);
+        list_for_each_entry(va, &vmap_area_list, list) {
+                if (!count)
+                        break;
+
+                if (!(va->flags & VM_VM_AREA))
+                        continue;
+
+                vm = va->vm;
+                vaddr = (char *) vm->addr;
+                if (addr >= vaddr + vm->size - PAGE_SIZE)
                         continue;
                 while (addr < vaddr) {
                         if (count == 0)
@@ -2034,10 +2042,10 @@ long vread(char *buf, char *addr, unsigned long count)
                         addr++;
                         count--;
                 }
-                n = vaddr + tmp->size - PAGE_SIZE - addr;
+                n = vaddr + vm->size - PAGE_SIZE - addr;
                 if (n > count)
                         n = count;
-                if (!(tmp->flags & VM_IOREMAP))
+                if (!(vm->flags & VM_IOREMAP))
                         aligned_vread(buf, addr, n);
                 else /* IOREMAP area is treated as memory hole */
                         memset(buf, 0, n);
@@ -2046,7 +2054,7 @@ long vread(char *buf, char *addr, unsigned long count)
                 count -= n;
         }
 finished:
-        read_unlock(&vmlist_lock);
+        spin_unlock(&vmap_area_lock);
 
         if (buf == buf_start)
                 return 0;
@@ -2085,7 +2093,8 @@ finished:
 
 long vwrite(char *buf, char *addr, unsigned long count)
 {
-        struct vm_struct *tmp;
+        struct vmap_area *va;
+        struct vm_struct *vm;
         char *vaddr;
         unsigned long n, buflen;
         int copied = 0;
@@ -2095,10 +2104,17 @@ long vwrite(char *buf, char *addr, unsigned long count)
                 count = -(unsigned long) addr;
         buflen = count;
 
-        read_lock(&vmlist_lock);
-        for (tmp = vmlist; count && tmp; tmp = tmp->next) {
-                vaddr = (char *) tmp->addr;
-                if (addr >= vaddr + tmp->size - PAGE_SIZE)
+        spin_lock(&vmap_area_lock);
+        list_for_each_entry(va, &vmap_area_list, list) {
+                if (!count)
+                        break;
+
+                if (!(va->flags & VM_VM_AREA))
+                        continue;
+
+                vm = va->vm;
+                vaddr = (char *) vm->addr;
+                if (addr >= vaddr + vm->size - PAGE_SIZE)
                         continue;
                 while (addr < vaddr) {
                         if (count == 0)
@@ -2107,10 +2123,10 @@ long vwrite(char *buf, char *addr, unsigned long count)
                         addr++;
                         count--;
                 }
-                n = vaddr + tmp->size - PAGE_SIZE - addr;
+                n = vaddr + vm->size - PAGE_SIZE - addr;
                 if (n > count)
                         n = count;
-                if (!(tmp->flags & VM_IOREMAP)) {
+                if (!(vm->flags & VM_IOREMAP)) {
                         aligned_vwrite(buf, addr, n);
                         copied++;
                 }
@@ -2119,7 +2135,7 @@ long vwrite(char *buf, char *addr, unsigned long count)
                 count -= n;
         }
 finished:
-        read_unlock(&vmlist_lock);
+        spin_unlock(&vmap_area_lock);
         if (!copied)
                 return 0;
         return buflen;