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authorHugh Dickins <hugh@veritas.com>2005-10-29 18:16:08 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-29 21:40:38 -0700
commit7ee78232501ea9de2b6c8f10d32c9a0fee541357 (patch)
tree2041a36a13bdd8b096dfbf52b63a87739ea97d6b
parentfd3e42fcc888a773572282575d2fdbf5cfd6216e (diff)
[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>
-rw-r--r--kernel/fork.c9
1 files changed, 4 insertions, 5 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 0e7fe4a8a8d..2a587b3224e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -192,6 +192,8 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
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 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
}
/*
- * 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 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
goto out;
}
retval = 0;
-
out:
+ up_write(&mm->mmap_sem);
flush_tlb_mm(oldmm);
up_write(&oldmm->mmap_sem);
return retval;