mm/mempolicy: remove or narrow the lock on current

It is not necessary to hold the lock of current when setting nodemask of
a new policy.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200921040416.86185-1-richard.weiyang@linux.alibaba.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index eddbe4e..69ce708 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -875,13 +875,12 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
                goto out;
        }
 
-       task_lock(current);
        ret = mpol_set_nodemask(new, nodes, scratch);
        if (ret) {
-               task_unlock(current);
                mpol_put(new);
                goto out;
        }
+       task_lock(current);
        old = current->mempolicy;
        current->mempolicy = new;
        if (new && new->mode == MPOL_INTERLEAVE)
@@ -1324,9 +1323,7 @@ static long do_mbind(unsigned long start, unsigned long len,
                NODEMASK_SCRATCH(scratch);
                if (scratch) {
                        mmap_write_lock(mm);
-                       task_lock(current);
                        err = mpol_set_nodemask(new, nmask, scratch);
-                       task_unlock(current);
                        if (err)
                                mmap_write_unlock(mm);
                } else