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Commit 7ee78232 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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[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: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent fd3e42fc

kernel/fork.c

+4 −5
Original line number Diff line number Diff line
@@ -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;