[PATCH] mm: dup_mmap down new mmap_sem
One anomaly remains from when Andrea rationalized the responsibilities of
mmap_sem and page_table_lock: in dup_mmap we add vmas to the child holding its
page_table_lock, but not the mmap_sem which normally guards the vma list and
rbtree. Which could be an issue for unuse_mm: though since it just walks down
the list (today with page_table_lock, tomorrow not), it's probably okay. Will
need a memory barrier? Oh, keep it simple, Nick and I agreed, no harm in
taking child's mmap_sem here.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/fork.c b/kernel/fork.c
index 0e7fe4a..2a587b3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -192,6 +192,8 @@
down_write(&oldmm->mmap_sem);
flush_cache_mm(oldmm);
+ down_write(&mm->mmap_sem);
+
mm->locked_vm = 0;
mm->mmap = NULL;
mm->mmap_cache = NULL;
@@ -251,10 +253,7 @@
}
/*
- * Link in the new vma and copy the page table entries:
- * link in first so that swapoff can see swap entries.
- * Note that, exceptionally, here the vma is inserted
- * without holding mm->mmap_sem.
+ * Link in the new vma and copy the page table entries.
*/
spin_lock(&mm->page_table_lock);
*pprev = tmp;
@@ -275,8 +274,8 @@
goto out;
}
retval = 0;
-
out:
+ up_write(&mm->mmap_sem);
flush_tlb_mm(oldmm);
up_write(&oldmm->mmap_sem);
return retval;