On Sat, 16 Jul 2005, Paul Jackson wrote:
> On the other hand, I hear him saying we can't do it, because the
> locking cannot be safely handled.
Here is one approach to locking using xchg. This is restricted only to the
policy fields on task_struct and vm_area_struct. One could also
synchronize by taking the alloc_lock in task_struct. I did not use xchg
during the population of vm_area_struct and task_struct and also not
during the destruction of these structures.
There may be additional races that need to be dealt with depending on
when the task struct and vm_area_struct become visible through the /proc
filesystem. However, these races are then general races affecting the use
of other fields in the
/proc filesystem.
Signed-off-by: Christoph Lameter <[EMAIL PROTECTED]>
Index: linux-2.6.13-rc3/mm/mempolicy.c
===================================================================
--- linux-2.6.13-rc3.orig/mm/mempolicy.c 2005-07-16 20:07:04.000000000
-0700
+++ linux-2.6.13-rc3/mm/mempolicy.c 2005-07-16 20:07:06.000000000 -0700
@@ -349,7 +349,7 @@ check_range(struct mm_struct *mm, unsign
static int policy_vma(struct vm_area_struct *vma, struct mempolicy *new)
{
int err = 0;
- struct mempolicy *old = vma->vm_policy;
+ struct mempolicy *old;
PDprintk("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy %p\n",
vma->vm_start, vma->vm_end, vma->vm_pgoff,
@@ -360,7 +360,7 @@ static int policy_vma(struct vm_area_str
err = vma->vm_ops->set_policy(vma, new);
if (!err) {
mpol_get(new);
- vma->vm_policy = new;
+ old = xchg(&vma->vm_policy, new);
mpol_free(old);
}
return err;
@@ -451,8 +451,7 @@ asmlinkage long sys_set_mempolicy(int mo
new = mpol_new(mode, nodes);
if (IS_ERR(new))
return PTR_ERR(new);
- mpol_free(current->mempolicy);
- current->mempolicy = new;
+ mpol_free(xchg(¤t->mempolicy, new));
if (new && new->policy == MPOL_INTERLEAVE)
current->il_next = find_first_bit(new->v.nodes, MAX_NUMNODES);
return 0;
Index: linux-2.6.13-rc3/kernel/exit.c
===================================================================
--- linux-2.6.13-rc3.orig/kernel/exit.c 2005-07-12 21:46:46.000000000 -0700
+++ linux-2.6.13-rc3/kernel/exit.c 2005-07-16 20:07:06.000000000 -0700
@@ -851,8 +851,7 @@ fastcall NORET_TYPE void do_exit(long co
tsk->exit_code = code;
exit_notify(tsk);
#ifdef CONFIG_NUMA
- mpol_free(tsk->mempolicy);
- tsk->mempolicy = NULL;
+ mpol_free(xchg(&tsk->mempolicy, NULL));
#endif
BUG_ON(!(current->flags & PF_DEAD));
Index: linux-2.6.13-rc3/include/linux/mm.h
===================================================================
--- linux-2.6.13-rc3.orig/include/linux/mm.h 2005-07-12 21:46:46.000000000
-0700
+++ linux-2.6.13-rc3/include/linux/mm.h 2005-07-16 20:07:06.000000000 -0700
@@ -107,7 +107,9 @@ struct vm_area_struct {
atomic_t vm_usage; /* refcount (VMAs shared if !MMU) */
#endif
#ifdef CONFIG_NUMA
- struct mempolicy *vm_policy; /* NUMA policy for the VMA */
+ struct mempolicy *vm_policy; /* NUMA policy for the VMA, may be
updated only
+ * with xchg or cmpxchg
+ */
#endif
};
Index: linux-2.6.13-rc3/include/linux/sched.h
===================================================================
--- linux-2.6.13-rc3.orig/include/linux/sched.h 2005-07-16 19:54:14.000000000
-0700
+++ linux-2.6.13-rc3/include/linux/sched.h 2005-07-16 20:07:06.000000000
-0700
@@ -761,7 +761,10 @@ struct task_struct {
clock_t acct_stimexpd; /* clock_t-converted stime since last update */
#endif
#ifdef CONFIG_NUMA
- struct mempolicy *mempolicy;
+ struct mempolicy *mempolicy; /* Only update via xchg or cmpxchg
because mempolicy
+ * may be changed from outside of the
process
+ * context
+ */
short il_next;
#endif
#ifdef CONFIG_CPUSETS
Index: linux-2.6.13-rc3/fs/proc/task_mmu.c
===================================================================
--- linux-2.6.13-rc3.orig/fs/proc/task_mmu.c 2005-07-16 20:07:04.000000000
-0700
+++ linux-2.6.13-rc3/fs/proc/task_mmu.c 2005-07-16 20:08:49.000000000 -0700
@@ -357,7 +357,7 @@ static ssize_t numa_policy_write(struct
{
struct task_struct *task = proc_task(file->f_dentry->d_inode);
char buffer[MAX_MEMPOL_STRING_SIZE], *end;
- struct mempolicy *pol, *old_policy;
+ struct mempolicy *pol;
if (!capable(CAP_SYS_RESOURCE))
return -EPERM;
@@ -373,17 +373,10 @@ static ssize_t numa_policy_write(struct
if (*end == '\n')
end++;
- old_policy = task->mempolicy;
+ if (pol->policy == MPOL_DEFAULT)
+ pol = NULL;
-
- if (!mpol_equal(pol, old_policy)) {
- if (pol->policy == MPOL_DEFAULT)
- pol = NULL;
-
- task->mempolicy = pol;
- mpol_free(old_policy);
- } else
- mpol_free(pol);
+ mpol_free(xchg(&task->mempolicy, pol));
return end - buffer;
}
@@ -402,7 +395,7 @@ static ssize_t numa_vma_policy_write(str
unsigned long addr;
char buffer[MAX_MEMPOL_STRING_SIZE];
char *p, *end;
- struct mempolicy *pol, *old_policy;
+ struct mempolicy *pol;
if (!capable(CAP_SYS_RESOURCE))
return -EPERM;
@@ -426,16 +419,10 @@ static ssize_t numa_vma_policy_write(str
if (*end == '\n')
end++;
- old_policy = vma->vm_policy;
+ if (pol->policy == MPOL_DEFAULT)
+ pol = NULL;
- if (!mpol_equal(pol, old_policy)) {
- if (pol->policy == MPOL_DEFAULT)
- pol = NULL;
-
- vma->vm_policy = pol;
- mpol_free(old_policy);
- } else
- mpol_free(pol);
+ mpol_free(xchg(&vma->vm_policy, pol));
return end - buffer;
}
-
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